Over a period of 20 years, from 1995 to 2015, in the absence of any switching to HnBs or ECigs and with the patterns of prevalence of cigarette smoking as existing in Germany, we estimate that there would have been 852,357 SRDs from LC, COPD, IHD, and stroke combined for both sexes, with about 8.61 million YLL.
In the work described here, we attempt to estimate how these numbers would have been affected had various alternative patterns of product use occurred. The greatest impact would clearly have occurred had all cigarette smokers quit in 1995, with no further use of cigarettes, HnBs, or ECigs (Scenario 1), resulting in a DD of 216,650 and 2.88 million YLS. However, substantial reductions would still have occurred had cigarette smoking in Germany been immediately replaced by either HnB use (Scenario 2; 159,278 DDs and 2.06 million YLS, corresponding to 74% and 71%, respectively, of Scenario 1, immediate cessation) or equally by either HnB or ECig use (Scenario 3; 179,470 DDs and 2.34 million YLS, corresponding to 83% and 81% of Scenario 1), with the greater numbers for Scenario 3 reflecting the assumed lower effective dose for ECigs compared with HnBs. These numbers would have been greater still had we included a Scenario in which cigarette smoking was immediately replaced by ECig use.
In practice, such Scenarios are rather unrealistic; more plausible are the estimates associated with the Pragmatic Scenarios in which a proportion of cigarette smokers move gradually to use HnBs and ECigs. Scenarios 4 to 7 vary in the extents to which uptake of these RRPs occurs and to which RRP users fully convert to exclusive RRP use rather than becoming multiple users of Cigarettes and RRPs. However, each Scenario shows a relevant population health impact, with DDs varying, between Scenarios 4 and 7, from 39,818 to 81,293 and YLS varying from 0.50 to 1.05 million. The different Pragmatic Scenarios would thus have achieved 18–38% for DDs and 17–36% for YLS of the effect of immediate cessation (Scenario 1), the best albeit unrealistic scenario.
Our estimates may be regarded as conservative for three main reasons. The first reason is that we only considered deaths from the four main SRDs because of the lack of reliable data on RR and H for all diseases associated with smoking. We have noted elsewhere [27] that our estimates of deaths saved would have to be multiplied by about 1.52 to yield an estimate for all smoking-related diseases.
The second, and very important, reason is that we only considered a 20-year follow-up period. This was because we did not wish to project into the future, where disease rates might be affected by a variety of exogenous factors, such as improvements in disease treatment. It is clear from the results in Fig. 3 that the annual numbers of lives saved increase rapidly over time, particularly from LC and COPD, where quitting takes a long time to reduce risk.
The third reason is that our analyses did not take into account the possibility that cigarette smokers who take up ECigs or HnBs might be more likely to quit cigarette smoking than those who continued to exclusively smoke cigarettes. Evidence from the US shows that use of ECigs is associated with increased cessation rates [42].
Our analyses are limited by a number of factors shown in a previous work [24] to have only a modest effect on the estimates of population health impact. These include failure to consider pipe and cigar smoking, use of smokeless tobacco or nicotine replacement therapy, ignoring exposure from environmental tobacco smoke, and not allowing TPs to vary by previous product use history. Though the negative exponential model has been validated on the basis of extensive data on quitting as well as limited data on changes in the number of cigarettes smoked [43], the accuracy of its predictions on more complex changes in usage over time has not been formally tested.
Our results related to the introduction of RRPs will be affected by the choice of effective doses used. For ECigs, we have used an estimate of 0.05 on the basis of expert opinion [38], although this estimate was derived on the basis of chemistry and short-term toxicological results. For HnBs, our estimate of 0.20 was conservatively based on biomarker and clinical data [37], with results for a number of endpoints suggesting a lower effective dose. Elsewhere [24], we have demonstrated that the estimated DD is linearly related to the assumed values of the effective dose used, with DD increasing as the effective dose decreases. While the estimated effective dose is an important factor when smokers switch to RRPs like ECigs and HnBs, other factors also play a role. These include changes in the frequency of use and the extent to which cigarettes are completely abandoned.
A possible limitation of our modelling is that we considered people who simultaneously used two or three out of cigarettes, ECigs, and HnBs as multiple-product users, with their effective dose taken as the mean of 1, 0.05, and 0.20. People who are dual users of cigarettes with either ECigs or HnBs might have a higher effective dose than the mean, while those who are dual users of ECigs and HnBs might have a lower effective dose. However, because the proportion of multiple product users is quite low, particularly for the Conversion and Full Conversion Scenarios, the overall effect of this limitation on the results seems likely to be quite modest.
A further possible limitation of our modeling is that we did not consider oral tobacco products like snus, the reason being that snus is not on the market in the EU outside of Sweden. Undoubtedly, snus can have a large positive impact on public health when smokers switch to it [16]. With other forms of oral tobacco having become available in Germany over the past years, uptake of such products could thus increase the overall effect on DD and YLS in the case of smokers switching to products without tobacco combustion, as has already been modelled in Sweden [44].
The rate at which smokers switch to less harmful alternatives like ECigs and HnBs is likely to depend on product risk perception, a large body of evidence having already shown this to be the case for ECigs. For instance, accurately perceiving ECigs as less harmful than cigarettes predicted subsequent ECig use among British smokers [45] and continues to correlate with ECig use among UK smokers [46]. German smokers were more likely to use ECigs for smoking cessation if they perceived them as less harmful than Cigarettes [47]. US adult dual users of ECigs and Cigarettes who perceived ECigs as less harmful than cigarettes were more likely to switch to exclusive ECig use 1 year later [48]. However, correct risk perceptions of ECigs remain low and are getting worse over time, both internationally [45, 46] and in Germany, where more than half of the population perceives ECigs [49, 50] and HnBs [50] as at least as harmful as cigarettes. Even among ever-users of HnBs in Germany, only just over half of them accurately perceived HnBs as less harmful than cigarettes [51]. Public health experts in the UK, the US, and Germany are, therefore, calling for better access to fact-based information [9, 45, 52, 53]. Educational campaigns via trusted public health institutions are likely the most effective tool [54]. While such campaigns exist in the UK, they are virtually absent in Germany.
Intuitively, maximizing the beneficial population health impact of introducing ECigs and HnBs will require a combination of high uptake among smokers, with many ultimately becoming exclusive RRP users. Our modeling results support this notion, with the DD and YLS increasing between Scenarios 4 and 5, when uptake was increased, and between Scenarios 5 and 7, when exclusive product use was increased. As discussed above, RR perceptions for ECig/HnB vs. smoking are potential drivers for both product uptake and exclusive product use, with health policy actions like public education campaigns being a recommended tool. Other factors likely to have an impact include risk-proportionate regulation in general [55]—such as product health warnings [56]—and local smoking cessation guidelines and healthcare professional recommendations [57] as well as media headlines [58]. Moreover, fiscal policies can have an impact on relative product use. Recent US retail panel data suggest that ECig taxation increased cigarette sales [59].
Many other published papers have attempted to quantify the population health impact of introducing RRPs. These include estimates based on the methodology we have used, but applied to the USA [24, 25] or Japan [26], as well as attempts using different methodology, supported by other tobacco companies [60–65] or by public funding [66–72]. Despite methodological differences, most modelers have assumed that the risk from RRP use, relative to that from cigarette smoking, is low and have concluded as we have that introduction of RRPs is likely to have a beneficial impact. For example, Levy et al. [69] concluded that “The tobacco control community has been divided regarding the role of e-cigarettes in tobacco control. Our projections show that a strategy of replacing cigarette smoking with vaping would yield substantial life year gains, even under pessimistic assumptions regarding cessation, initiation and relative harm.” Although this previous paper focused on e-cigarettes, the authors did note that “…heat-not-burn tobacco products have been introduced in some countries, and these may be a better substitute for cigarettes than e-cigarettes…”
As noted in the introduction, the number of smoking-attributable deaths estimated by Mons and Brenner to have occurred in Germany in 2013 is 125,000 [6]. In the Null Scenario, in 2013, the number of SRDs was estimated to be 39,629. There are three main reasons for this discrepancy. First, we only considered four diseases, which form only about 67.5% of the total number of smoking-related diseases [2]. Second, we only considered the deaths of people aged 30–79 years, whereas the published estimate was related to age 35 years or above. Third, the disease-specific RRs used by Mons [2] were derived from specific US studies, whereas ours were derived from detailed meta-analyses (see Table 5). While the RRs from the two studies were quite similar for both IHD and stroke, those for LC (23.26 for men and 12.69 for women vs. 11.68 for both sexes) and COPD (10.58 for men and 13.08 for women vs. 4.56 for both sexes) were markedly higher in the previous study. Had we considered more diseases, a wider age range, or higher RRs, the estimated DD and YLS would, of course, have increased.
Overall, our results provide insight into how much the introduction of the two RRPs considered might affect the distribution of usage in Germany and the mortality related to cigarette smoking. Policies and regulation can accelerate switching to these RRPs, including calling for a more risk-proportionate approach and for the best available information on RRPs to be available to adult smokers. This will help increase the perception of the harm-reduction capabilities of RRPs and encourage switching, make alternatives to cigarettes more attractive for smokers, and help maintain product standards for building consumer trust in RRPs. Rather than any single measure, an integrated tobacco control strategy is likely to be more successful in encouraging smokers to switch to RRPs and thus result in an overall public health gain.