NOT PEER REVIEWED
We welcome discussion of our research even when it comes from those whose view on accepting tobacco industry funding is very different from ours. Tomaselli and Caponnetto, from the Center of Excellence for the acceleration of HArm Reduction (CoEHAR),[1] a group funded by the Foundation for a Smoke-Free World (FSFW), an organisation established by Philip Morris International (PMI) with funding of US$1 billion that promotes electronic cigarettes (e-cigarette) and heated tobacco products (HTP),[2] take issue with our finding [3] that these products increase smoking initiation and relapse and reduce quitting. [4]
First, we are puzzled by their main criticism. Of course we agree that smokers who have failed to quit, ex-smokers prone to relapse, and never smokers prone to engage in addictive behaviours could be overrepresented among the baseline e-cigarette or HTP users in our study.[4] But this does not undermine our main conclusions. Even if we were to assume that either none or all novel product users in our cohort were more prone to addiction, our results would still be incompatible with the argument, which underpins the work of FSFW, that these products can reduce smoking conventional cigarettes when used as consumer products.
Second, we hope that they agree with us that we should consider the totality of evidence on a topic as it is rare for a single study to provide a definitive answer, and especially given the record of the tobacco industry in cherry picking those bits that support their case.[5] Their concern about motivation of users was addressed in the US PATH cohort study. This rejected the hypothesis that e-cigarettes as consumer products are effective quit aids even when being used for this purpose, rather than as a recreational product.[6] It compared recent quitters using e-cigarettes during their last quit attempts with those using any pharmaceutical aid, finding that smokers who reported using e-cigarettes in their most recent quit attempt were less likely to successfully quit, and that subjects who switched to e-cigarettes reported higher relapse rates than attempters who did not use e-cigarettes to quit.[6] Similarly, a meta-analysis of 20 observational studies found that, when restricting the analyses to participants who wanted to quit, the odds ratio (OR) of smoking cessation for users of e-cigarettes as compared to non-users was 0.85 (95% confidence interval: 0.68-1.06).[7] Although we did not report it in our paper,[3] we did collect information on quit attempts over the past month among current smokers in our study: all four e-cigarette users and four HTP users who made any quit attempt continued smoking at follow-up.
Tomaselli and Caponnetto also express concern around the fact that we considered current product user, a classification that includes both occasional and daily users. Although we had collected the information on occasional vs. daily use of these products, several models to estimate relative risk (RR) did not converge when these were analysed separately, while combining them generated more stable and robust RR estimates.[3] Table 1 (available online at: http://www.epideuro.eu/wp-content/uploads/2022/12/Table1.pdf) shows OR estimates also considering occasional and daily users separately. The association between HTP regular use and relapse did not reach statistical significance. This is almost certainly because of the small number, eight, of ex-smokers who were regular HTP users. This does not change the key message of our study: the use (both occasional and regular) of e-cigarettes and HTPs predicts smoking initiation and relapse, and appear to reduce smoking cessation rates.
Tomaselli and Caponnetto point to the last Cochrane Review of randomized controlled trials (RCT) comparing e-cigarettes with nicotine replacement therapy (NRT) for smoking cessation.[8] However, this has almost no relevance to our findings. We do not dispute that any form of nicotine delivery can aid cessation when part of a structured and time-limited therapeutic package supported by behavioural interventions. This is entirely different from their use as a consumer product. However, as they mention this review, we feel obliged to raise our concerns on its findings, including: i) the extremely low success rate (e-cigarettes fail in 90% of cases)[8]: ii) no RCT compares e-cigarettes with standard care in clinical settings (i.e., varenicline or bupropion or cytisine), by far more effective in smoking cessation according to other Cochrane Library reviews;[8, 9] iii) e-cigarettes are heterogeneous products so those used in RCTs cannot be considered representative of all products; and iv) more than 80% of those quitting through e-cigarette continue its use after treatment,[8] increasing the risk of relapse, as outlined in our study.[3] More importantly, our study concurs with the totality of the scientific literature that, when used as a consumer product, e-cigarettes are not effective in increasing smoking cessation.[7]
To study the individual trajectories of conventional cigarette smoking in the general population (including non-smokers) outside the clinical setting, interventional studies are clearly not an option. Hence, we are forced to rely on observational studies, with prospective cohort studies best able to reduce risk of bias and increase reliability and generalizability. To our knowledge, our study is the first cohort designed so far involving the general population, at least in Europe. It supports findings from other Italian cross-sectional studies[10] and analyses of trends of the prevalence of conventional cigarette smoking (for the first time substantially increasing after seven decades of continuous decrease) and sales of conventional cigarettes (for the first time no more decreasing after two decades of substantial fall).[11]
Our assessment of the totality of the evidence, including our findings, persuades us that these products represent a threat to tobacco control and we remain unconvinced by the arguments by those associated with CoEHAR whose commentaries challenge the accumulating evidence opposing novel nicotine-containing products undertaken by researchers without conflicts of interests.[12]

References
1. Tobacco Tactics. Centre of Excellence for the Acceleration of Harm Reduction (CoEHAR) (available online at: https://tobaccotactics.org/wiki/coehar/; last access 13 December 2022). 2022.
2. van der Eijk Y, Bero LA, Malone RE. Philip Morris International-funded 'Foundation for a Smoke-Free World': analysing its claims of independence. Tob Control 2019; 28: 712-718.
3. Gallus S, Stival C, McKee M et al. Impact of electronic cigarette and heated tobacco product on conventional smoking: an Italian prospective cohort study conducted during the COVID-19 pandemic. Tob Control 2022.
4. Tomaselli V, Caponnetto P. Inappropriate study design cannot predict smoking initiation and relapse with e-cigarette and heated tobacco product use. Tob Control 2022.
5. Diethelm P, McKee M. Denialism: what is it and how should scientists respond? Eur J Public Health 2009; 19: 2-4.
6. Chen R, Pierce JP, Leas EC et al. Effectiveness of e-cigarettes as aids for smoking cessation: evidence from the PATH Study cohort, 2017-2019. Tob Control 2022.
7. Wang RJ, Bhadriraju S, Glantz SA. E-Cigarette Use and Adult Cigarette Smoking Cessation: A Meta-Analysis. Am J Public Health 2021; 111: 230-246.
8. Hartmann-Boyce J, Lindson N, Butler AR et al. Electronic cigarettes for smoking cessation. Cochrane Database Syst Rev 2022; 11: CD010216.
9. Howes S, Hartmann-Boyce J, Livingstone-Banks J et al. Antidepressants for smoking cessation. Cochrane Database Syst Rev 2020; 4: CD000031.
10. Liu X, Lugo A, Davoli E et al. Electronic cigarettes in Italy: a tool for harm reduction or a gateway to smoking tobacco? Tob Control 2020; 29: 148-152.
11. Gallus S, Borroni E, Odone A et al. The Role of Novel (Tobacco) Products on Tobacco Control in Italy. Int J Environ Res Public Health 2021; 18.
12. Polosa R, Farsalinos K. A tale of flawed e-cigarette research undetected by defective peer review process. Intern Emerg Med 2022.

NOT PEER REVIEWED
The study by Gallus et al. [1] sought to establish whether electronic cigarettes (ECs) and heated
tobacco products (HTPs) reduce or increase the probability of smoking in a cohort of Italian
participants and concluded that both EC and HTP use predict smoking initiation and relapse
among respondents. We would like to raise some concerns about the interpretation of the study
findings. The study suffers from a potentially crucial bias of the outcome being present at baseline, as
compared non-users with people who were already using products at baseline. Specifically,
smokers who were using ECs or HTPs at baseline may already represent failed attempts to quit at
baseline. Additionally, ex-smokers using these products may have already been in a trajectory to
relapse to smoking at, or even long before, baseline, and may in fact have initiated such product
use in order to avoid relapse. Still, this group may represent ex-smokers who were at higher risk
for relapsing at baseline compared to ex-smokers who did not use these products. Similarly,
never smokers who use novel nicotine products may represent individuals prone to the
engagement of an inhalational habit. Therefore, they would be more likely to initiate smoking.
The situation is very similar to assessing if people who drink beer at baseline are more likely to
drink whiskey at follow up compared to non-drinkers of beer. People who want to use alcohol
and are using alcohol at baseline, would be much more likely to use stronger liquor at follow up
compared to those who do not use alcohol. This represents a typical case of the common liability
model of addressing risk behaviors, which has been frequently misinterpreted as a “gateway”
theory. Moreover, the study design does not allow for any assessment of the motivations to use these
products. It is unclear if and how many participants were using nicotine products in an attempt to
quit (for smokers) or an attempt to prevent relapse (for ex-smokers) instead of simply
experimenting out of curiosity. Notably, while the study examined daily use through the
questionnaire, results were presented only for current users, a classification that includes both
occasional and daily users. Studies have shown that classifying daily and occasional users in the
same group can often be misleading (2-5), since frequency of use is an indirect indicator of
motivation for use (6), but also a determinant of their success as smoking substitutes (7). The study also suffers from the unpredictability of conducting surveys during COVID-19
lockdowns. Of note, there is convincing evidence that the coronavirus outbreak has had a
negative impact, inducing or exacerbating addictive behaviors as coping mechanisms. It is
possible that smokers preferred smoking – rather than alternatives – depending on their level of
distress (8,9).
Last but not least, the latest Cochrane Review finds high certainty evidence that nicotine e-cigarettes
are more effective than traditional nicotine-replacement therapy (NRT) in helping people quit
smoking (10). In conclusion, methodological issues of the study design makes it inappropriate to address the
research question.

1. Gallus S, Stival C, McKee M, Carreras G, Gorini G, Odone A, van den Brandt PA,
Pacifici R, Lugo A. Impact of electronic cigarette and heated tobacco product on
conventional smoking: an Italian prospective cohort study conducted during the COVID19 pandemic. Tob Control. 2022 Oct 7:tobaccocontrol-2022-057368. doi: 10.1136/tc2022-057368.
2. Hitchman SC, Brose LS, Brown J, Robson D, McNeill A. Associations Between ECigarette Type, Frequency of Use, and Quitting Smoking: Findings From a Longitudinal
Online Panel Survey in Great Britain. Nicotine Tob Res 2015;17:1187-94.
3. Farsalinos, K. E.; Poulas, K.; Voudris, V.; & Le Houezec, J. Prevalence and correlates of
current daily use of electronic cigarettes in the European Union: analysis of the 2014
Eurobarometer survey. 2017, Internal and emergency medicine, 12(6), 757–763.
https://doi.org/10.1007/s11739-017-1643-7
4. Farsalinos, K. E.; & Barbouni, A. Association between electronic cigarette use and
smoking cessation in the European Union in 2017: analysis of a representative sample of
13 057 Europeans from 28 countries. 2021, Tobacco control, 30(1), 71–76.
https://doi.org/10.1136/tobaccocontrol-2019-055190
5. Farsalinos, K. E.; Polosa, R.; Cibella, F.; & Niaura, R. Is e-cigarette use associated with
coronary heart disease and myocardial infarction? Insights from the 2016 and 2017
National Health Interview Surveys. 2019, Therapeutic advances in chronic disease, 10,
2040622319877741. https://doi.org/10.1177/2040622319877741.
6. Amato MS, Boyle RG, Levy D. How to define e-cigarette prevalence? Finding clues in
the use frequency distribution. Tob Control. 2016 Apr;25(e1):e24-9. doi:
10.1136/tobaccocontrol-2015-052236
7. Harlow AF, Stokes AC, Brooks DR, Benjamin EJ, Leventhal AM, McConnell RS,
Barrington-Trimis JL, Ross CS. Prospective association between e-cigarette use
frequency patterns and cigarette smoking abstinence among adult cigarette smokers in the
United States. Addiction. 2022 Dec;117(12):3129-3139. doi: 10.1111/add.16009.
8. Avena NM; Simkus J; Lewandowski A; Gold MS; Potenza MN. Substance Use
Disorders and Behavioral Addictions During the COVID-19 Pandemic and COVID-19-
Related Restrictions. Front Psychiatry. 2021;12:653674.
HTTPS://doi.org/10.3389/fpsyt.2021.653674
9. Caponnetto, P.; Inguscio, L.; Saitta, C.; Maglia, M.; Benfatto, F.; & Polosa, R. Smoking
behavior and psychological dynamics during COVID-19 social distancing and stay-athome policies: A survey. 2020, Health Psychology Research, 8(1).
https://doi.org/10.4081/hpr.2020.9124
10. Hartmann-Boyce J; Lindson N; Butler AR; McRobbie H; Bullen C; Begh R; Theodoulou
A; Notley C; Rigotti NA; Turner T; Fanshawe TR; Hajek P. Electronic cigarettes for
smoking cessation. 2022, Cochrane Database of Systematic Reviews 2022, Issue 11. Art.
No.: CD010216. DOI: 10.1002/14651858.CD010216.pub7.
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010216.pub7/...
s

The paper by Asfar et al (1) had a noble objective, which was to inform ENDS health risk communications by updating the 2018 evidence review by the US. National Academies of Sciences, Engineering and Medicine (NASEM) (2). The need for improved risk communications about ENDS is reinforced by a recent study which found that only 17.4% of US smokers believe that nicotine vaping is safer than smoking (3). While ENDS use is not safe, the evidence from toxicant exposure studies does show that ENDS use is far safer than smoking cigarettes and may benefit public health by assisting those who smoke to quit smoking (4, 5).
An important limitation of the umbrella review method utilized by the authors is that it does not directly attempt to systematically characterize new research. This is a concern because the marketplace of ENDS products used by consumers has evolved since the 2018 NASEM report (4, 5). Furthermore, the authors have included some meta-analyses of selected reviews for some domains, but these meta-analyses were not in the Prospero pre-registration (6), nor explained in the paper. It’s thus unclear how or why certain reviews were selected for meta-analysis, and also whether the comparators are the same for these reviews. More importantly, these meta-analyses risk single studies contributing multiple times to the same pooled estimate. The authors noted this as a limitation commenting inaccurately that ‘it was impossible to identify articles that were included in multiple reviews’. In our view this serious methodological flaw merits removal of all pooled estimates from their analyses. Additionally in several places, association is conflated with causality (e.g. “ENDS use impedes smoking cessation”) when based on observational data. The classification of evidence is also not transparent, cannot be found in the source the authors cited, and in places does not follow from the evidence presented (e.g. gateway evidence classified as high when based on observational studies).
The review also excludes research reviews supported by ENDS manufacturers. While we recognize and agree with the authors’ concerns about possible bias in industry publishing, we also believe that the exclusion of such research without any analysis of the scientific merits of the research itself precludes a comprehensive assessment of the scientific literature regarding the health risks of ENDS. Also, excluding industry publications necessarily eliminates from consideration evidence that the Center for Tobacco Products may be asked to consider when it is reviewing product applications for product marketing authorizations and modified risk claims.
The paper falls short, as well, in addressing the risk communication implications of the findings since the authors’ recommendations often do not match the evidence of what is known and not known about the risks of using ENDS. A careful analysis of suggested risk messages contained in supplementary material to the paper finds messages that do not appear to be supported by the evidence reviewed in the paper. For example, the suggested risk messages that "nicotine in vapes can harm memory, concentration, and learning in young people," "vaping nicotine can harm learning ability in young people," and "exposure to nicotine during adolescence can interfere with brain development" do not appear to be derived from a comprehensive review of scientific evidence. The evidence of nicotine having adverse effects on brain development or learning in adolescents comes primarily from rodent studies where dosing of nicotine is not necessarily analogous to exposure from ENDS.
For most of the topics reviewed, the umbrella review reveals that the health risks of ENDS remain unsettled at this time. Whilst biomarker exposure data clearly indicate reduced risk compared to tobacco cigarettes (4), we would suggest restraint is needed in communicating absolute risk information to the public (7). Also we would go one step further in noting that whatever the health risks of ENDS may be, they are going to be most observable in those persons using ENDS on a persistent basis for months or years at a minimum. For example, the health risks of cigarette smoking do not reliably emerge until after smokers exceed 10 pack-years or more of exposure (87). Few studies of ENDS health risks have actually focused on the likely higher risk group of persistent ENDS users (4).
We also take issue with the paper’s main conclusion that direct comparison between the harms of cigarettes and ENDS should be avoided (1). In fact, such comparisons are likely unavoidable and necessary since the group most likely to use ENDS on a persistent basis are those who have a history of cigarette use. Moreover, ENDS were originally developed as a cessation aid and evaluations of cessation aids almost always incorporate evidence on the relative harms compared to continuing to smoke. We do recognize that accounting for a person’s smoking history complicates evaluations of the health risks of ENDS, but dismissing such comparisons simply ignores the fact that ENDS are existing or potential cigarette substitutes for many smokers (4, 5). A recent review of biomarker studies found that compared to smoking, using ENDS leads to a substantial reduction in biomarkers of toxicant exposure associated with cigarette smoking, while also acknowledging that the degree of any residual risk from smoking remains unclear because of the lack of comparisons between long-term former smokers, and with those who have never smoked or used ENDS (4).
Communicating health risk information about ENDS has to have some context to be meaningful to consumers. A common misconception about tobacco use is that the most dangerous component of the product is nicotine (9-14). However, while nicotine can be addictive, it is the other toxicants in tobacco, especially burned tobacco, that are the true culprits of tobacco-related diseases (2, 4). Thus, when communicating information about the health risks of tobacco products, it makes sense to provide consumers with information about the relative health dangers from burned compared to unburned tobacco products. The example risk messages included in the supplementary materials to the paper appear to be developed with a goal of discouraging anyone from using a vaping product rather than to inform potential users about risks.
Public health authorities can reduce the risk of misinforming or confusing the public by acknowledging when evidence is incomplete or based on statistical association rather than clear evidence of causality, and by updating any statements or recommendations quickly when plausibly causal evidence becomes available (7).

 
References
1. Asfar T, Jebai R, Li W, et al. Risk and safety profile of electronic nicotine delivery systems (ENDS): an umbrella review to inform ENDS health communication strategies. Tob Control Epub ahead of print: [please include Day Month Year]. doi:10.1136/ tobaccocontrol-2022-057495
2. National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Population Health and Public Health Practice; Committee on the Review of the Health Effects of Electronic Nicotine Delivery Systems. Public Health Consequences of E-Cigarettes. Eaton DL, Kwan LY, Stratton K, editors. Washington (DC): National Academies Press (US); 2018 Jan 23.
3. Kim S, Shiffman S, Sembower MA. US adult smokers' perceived relative risk on ENDS and its effects on their transitions between cigarettes and ENDS. BMC Public Health. 2022 Sep 19;22(1):1771. doi: 10.1186/s12889-022-14168-8.
4. McNeill, A, Simonavičius, E, Brose, LS, Taylor, E, East, K, Zuikova, E, Calder, R and Robson, D (2022). Nicotine vaping in England: an evidence update including health risks and perceptions, September 2022. A report commissioned by the Office for Health Improvement and Disparities. London: Office for Health Improvement and Disparities.
5. Balfour DJK, Benowitz NL, Colby SM, Hatsukami DK, Lando HA, Leischow SJ, Lerman C, Mermelstein RJ, Niaura R, Perkins KA, Pomerleau OF, Rigotti NA, Swan GE, Warner KE, West R. Balancing Consideration of the Risks and Benefits of E-Cigarettes. Am J Public Health. 2021 Sep;111(9):1661-1672.
6. Rime Jebai, Wei Li, Oluwole Olusanya Joshua, Beck Graefe, Celia Rubio. Systematic Review of Reviews on the Harmful Effects of Electronic Nicotine Delivery Systems: Building Evidence for Health Communication Messaging. PROSPERO 2021 CRD42021241630 Available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021241630
7. United States Surgeon General. Confronting Health Misinformation: The U.S. Surgeon General’ s Advisory on Building a Healthy Information Environment [Internet]. 2021 [cited 2022 Aug 9]. Available from: https://www.hhs.gov/sites/default/files/surgeon-general-misinformation-a...
8. Doll R, Peto R, Boreham J, Sutherland I. Mortality from cancer in relation to smoking: 50 years observations on British doctors. Br J Cancer. 2005 Feb 14;92(3):426-9. doi: 10.1038/sj.bjc.6602359.
9. O’Brien EK, Nguyen AB, Persoskie A, Hoffman AC. U.S. adults’ addiction and harm beliefs about nicotine and low nicotine cigarettes. Prev Med. 2017;96:94-100.
10. Steinberg MB, Bover-Manderski MT, Wackowski OA, Singh B, Strasser AA, Delnevo CD. Nicotine Risk Misperception Among US Physicians. J Gen Intern Med. 2021, 36(12):3888-3890.
11. Elton-Marshall T, Driezen P, Fong GT, et al. Adult perceptions of the relative harm of tobacco products and subsequent tobacco product use: Longitudinal findings from waves 1 and 2 of the population assessment of tobacco and health (PATH) study. Addict Behav. doi:10.1016/j.addbeh.2020.106337.
12. Parker MA, Villanti AC, Quisenberry AJ, Stanton CA, et al. Tobacco Product Harm Perceptions and New Use. Pediatrics. 2018 Dec;142(6):e20181505. doi: 10.1542/peds.2018-1505.
13. Yong HH, Gravely S, Borland R, Gartner C, et al. Perceptions of the Harmfulness of Nicotine Replacement Therapy and Nicotine Vaping Products as Compared to Cigarettes Influence Their Use as an Aid for Smoking Cessation? Findings from the ITC Four Country Smoking and Vaping Surveys. Nicotine Tob Res. 2022 Aug 6;24(9):1413-1421. doi: 10.1093/ntr/ntac087.
14. National Cancer Institute. Health Information National Trends Survey. HINTS 5 cycle 3, 2019. Available at: https://hints.cancer.gov/view-questions-topics/question-details.aspx?PK_...

NOT PEER REVIEWED
These arguments by Pesko and Friedman cannot undo the central flaw in the Friedman paper. We are surprised that Pesko and Friedman continue to argue that Friedman’s analysis of the YRBSS fall data as “after” data is valid despite the Friedman paper defining the exposure variable as follows: “A binary exposure variable captured whether a complete ban on flavoured tobacco product sales was in effect in the respondent’s district on January 1 of the survey year.”[1] If Friedman had intended to treat the period immediately after July 21 2018 as the “after” period, why had she not selected July 21 of each year as the cut-off date for indicating exposure to the policy effects? It seems apparent that Friedman chose the January 1, 2019 as the cut-off for “after” data because she knew this was the enforcement date and she assumed wrongly that the YRBSS data were collected after January 1, 2019. This is evident in her own response[2] to a critique[3] of her paper as we already noted in our previous response.[4]
Friedman states that “the official/legislated effective date are used to ensure that resulting estimates capture unconfounded responses to the policy change.” Again, if this approach made sense in the specific San Francisco case, why did Friedman use January 1, 2019 in her paper? Perhaps because it simply doesn’t make sense to attribute a policy’s effects before the policy is actually implemented. Similarly, the use of enforcement date rather than effective date is not at all as unusual as Pesko claims. Pesko and Friedman’s suggestion to use effective date post hoc simply does not make any logical sense in the San Francisco case, where there was an explicit and highly publicised period of non-enforcement as well as documented non-compliance with the policy through the period of survey administration. In fact, all the existing papers on the San Francisco flavour ban,[5–8] including the Friedman paper,[1] have used the January 1, 2019 enforcement date as the cut-off date for evaluating the policy implementation effects.
Friedman rightly points out that the San Francisco Department of Public Health didn’t even begin compliance inspections until December 3rd, 2018. The YRBSS survey was already nearly complete (fielded between November 5th and December 14th, 2018) at that time. In addition, the current smoking question assesses smoking in the past 30 days, meaning that all of the survey respondents would be reporting on their smoking behaviour for a preceding period that encompasses a time before compliance checks began. When compliance checks began in December, only 17% of retailers were found to be compliant with the flavour ban, likely because they were explicitly instructed that there would be no penalties until January 1, 2019. These facts mean that youths’ retail purchase access would not have changed appreciably at that time. Her conclusion in her paper that “reducing access to flavoured electronic nicotine delivery systems may motivate youths who would otherwise vape to substitute smoking”[1] is inconsistent with the fact that e-cigarettes were still widely available in San Francisco in the fall of 2018.
Pesko and Friedman cite Gammon et al. (2021) showing reduced e-cigarette sales[5] to argue that Friedman’s analysis is still valid because the law may have led to a decrease in youth’s demand for e-cigarettes before the enforcement date. In truth, the vaping rate went from 7.1% to 16% in San Francisco between 2017 and 2019. We note that the Friedman paper omitted reporting youth vaping prevalence,[1] stating that “Recent vaping was not considered because of likely confounding. California legalised recreational marijuana use the same year San Francisco’s flavour ban went into effect; in addition, the YRBSS’s vaping questions did not distinguish vaping nicotine vs marijuana.” The decision to not control for vaping in the Friedman analysis is not justified. Friedman wrote in her response[2] to three critiques[3,9,10] of the original paper that the reason was potential misclassification of marijuana vaping due to California’s legalisation of recreational marijuana because the YRBSS questions do not specify the substance being vaped. Marijuana exclusive vapers account for only about 1% of the youth population, making this an inappropriate reason to not control for significant differential changes in vaping over time in different cities.[11–13] For example, vaping rates went down in Oakland after the flavour restriction but were up significantly in the 2018 pre-enforcement period in San Francisco. Initiation of vaping nicotine has been associated with higher rates of subsequent use of cigarettes among adolescents.[14,15] Higher rates of vaping nicotine e-cigarettes may also have been the impetus for passage of the San Francisco flavour ban, making vaping an important confounder. Taken together, these facts make uncontrolled confounders a likely explanation to cigarette use differences across locations and therefore decreases the possibility that the cigarette smoking rate went up due to an unenforced flavour ban.
Pesko and Friedman did not mention that Gammon et al. (2021) reported the predicted flavoured nicotine e-cigarette sales in San Francisco increased from 3439 units per week pre-policy (July 2015-July 2018) to 5906 units per week in the effective period (July-December 2018) and only declined after the enforcement period (January-December 2019) to 16 units per week (Table 1 in their article).[5] Clearly, flavoured e-cigarettes were still widely available in the marketplace during the effective but non-enforced period and in fact, more flavoured e-cigarettes were sold during the effective period than prior to the policy. Furthermore, Friedman also did not mention that Gammon et al. (2021) reported that cigarette sales declined post flavour ban.[5] Predicted total cigarette sales in San Francisco declined from 83424 units per week pre-policy (July 2015-July 2018) to 77370 units per week in the effective period (July-December 2018) and further declined after the enforcement period (January-December 2019) to 64220 units per week (Table 1). [5] This pattern is therefore inconsistent with Friedman’s 2021 paper conclusion that “reducing access to flavoured electronic nicotine delivery systems may motivate youths who would otherwise vape to substitute smoking” in the fall of 2018. The fact is average weekly flavoured e-cigarette sales increased while total cigarette sales decreased in San Francisco between July-December 2018 compared to pre-policy period. [5] The substitution explanation falls apart. Pesko and Friedman cannot selectively use data to have it both ways.
As we described in our paper, after Oakland implemented a convenience store flavoured tobacco sales restriction in July 2018, high school youth vaping declined from 11.2% to 8.0% (p=0.04)[16] and smoking declined from 4.4% to 2.4% (p=0.02)[17] between 2017 and 2019. Our description that vaping and cigarette use prevalence declined was accurate. Upon reviewing the YRBSS data from the CDC, the Oakland data does in fact represent a statistically significant drop in vaping and smoking rate from 2017 to 2019. Friedman objects to our use of the Oakland (neighboring city to San Francisco) data as a comparison because Oakland’s law was less comprehensive than San Francisco’s. We respectfully disagree with Friedman’s objection. The Oakland law that drastically limited youth access to flavoured tobacco products in that city certainly informs the San Francisco case. The idea that the decline in cigarette smoking prevalence after the flavour ban in Oakland was less than the decline of cigarette smoking elsewhere is disproven by the fact that there was a greater drop in current smoking rate in Oakland from 2017 to 2019 (46% decline from 4.4% to 2.4%) compared to the average decrease nationally across the United States (32% decline from 8.8% to 6.0%) based on YRBSS data.[18]
Friedman offered several post hoc explanations for why youth cigarette smoking might increase following a flavour ban. She offers no data from San Francisco to support market responses following the SF flavour ban, nor does she provide data that SF youth had switched to using flavour accessories. These scenarios also assume that flavoured tobacco products were no longer available at the time of the SF YRBSS data collection, but we know products were still largely available as of December 2018 in 83% of the retailers. It is historically inaccurate for Friedman to suggest that the outbreak of EVALI had any bearing on potentially reducing people’s willingness to buy vaping products from informal sellers in 2018 because this outbreak occurred in the fall of 2019, one year after the SF YRBSS data were collected.
Our description about receiving the YRBSS survey collection date through an inquiry from the CDC was accurate.[19] The CDC informed us that the YRBSS in San Francisco was conducted in the fall of 2018 and we used this information in our paper. We wrote to the San Francisco School District to confirm these dates as did Dr. Friedman.
Liber’s points about partial compliance rates are refuted by the availability of flavoured products during the survey administration period and are addressed by our above response. We thank him for agreeing that this case highlights the need for including more precise date of data collection identifiers in publicly available data sets. Given the significance and potential impact of these analyses for public health policy, it behooves all users of publicly available data to pay close attention to dates of data collection in relation to policy effective/enforcement dates when analyzing this information, to seek confirmation if there is any doubt, and not make assumptions about the dates. In this case the dates of the 2019 YRBSS administration ranged widely from fall of 2018 (SF) to fall of 2019 (NYC).[19]
An important benefit of flavour ban legislation is that flavoured combustible tobacco use goes down.[7] The use rates of flavoured combustible little cigars and cigarillos are similar or exceed the combustible cigarette use rate among youth in San Francisco, [11] making flavour bans an important tool in decreasing overall youth combustible tobacco rates.
The results of the 2019-2020 California Student Tobacco Survey, which was conducted after the enforcement of the flavour ban showed that the prevalence of cigarette smoking among San Francisco high schoolers was 1.6% (compared with 4.7% based on the San Francisco 2017 pre-ban YRBSS data).[11] After the enforcement of the flavour ban, we now see historically low smoking rates in San Francisco. This data from the time after the flavour ban was actually implemented by retailers further calls into question the conclusion of the Friedman paper.
References
1 Friedman AS. A Difference-in-Differences Analysis of Youth Smoking and a Ban on Sales of Flavoured Tobacco Products in San Francisco, California. JAMA Pediatr 2021;175:863–5. doi:10.1001/jamapediatrics.2021.0922
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