EXPERT REACTION: COVID-19 vaccines likely prevented nearly 18,000 deaths in NSW's early Omicron era

Over the course of the COVID-19 pandemic, the Australian Bureau of Statistics and the Australian Actuaries Institute have published regular reports on excess deaths caused by COVID-19. Both organisations have used a counterfactual approach which asks what would have happened to death rates if the pandemic had not occurred? In other words, they have used historical trends in death rates to project future death rates, and then compared them to what is actually happening now.

However, neither organisation has looked at the impact of vaccinations on deaths from COVID-19. The paper just published by an Australian team has used a similar data-driven counterfactual approach to ask the question, what would death rates from COVID-19 be like if no vaccine was available? They also compared no vaccine to one, two, or three or more doses.

The authors only used data for NSW since “Access to full official Australian government datasets was not possible despite extensive efforts”. They focused on those aged 50+, since most COVID-deaths are in this age group. They examined data for the 48-week period 14 August 2021 to 9 July 2022. They did allow for excess deaths caused by waning immunity.

They found that unvaccinated individuals had 7.7 times the COVID-19 death rate compared to those with two or more doses. This increased to 11.2 times the death rate when comparing the unvaccinated to those who had one or more booster shots. In the total absence of a vaccination program, they estimated that over the 48-week period, there would have been 21,250 COVID-related deaths, six times the actual rate.

One mistake that vaccine sceptics keep bringing up is that the majority of COVID-related deaths are in those who have been vaccinated – therefore the vaccines do not work, or even cause death. The authors rightly point out that a fairer comparison is to look at the death rate in those unvaccinated compared to those vaccinated, which immediately shows how important the vaccination program has been in preventing COVID-19-associated deaths.

This paper estimates the deaths averted for 50+ year olds by vaccination against COVID-19 in NSW, finding that compared to a world where no one had been vaccinated and otherwise the same timeline (e.g. Delta playing out as it played out) and strategy (i.e. open up to world in late 2021 and early 2022, with Omicron sweeping through), there might have been about 17,700 more deaths.  Put another way, vaccination as we used it saved 17,700 lives. 

Another interesting comparison the study makes is with a counterfactual where everyone (i.e. actually everyone, not ‘just’ the 95% of 50+ year olds who got two doses) was vaccinated by the end of July 2021, then approximately a further 440 deaths would have been averted. 
 
Not reported by the authors, it is moot whether faster vaccine rollout that achieved the same uptake we had (i.e. not 100%) would have resulted in fewer deaths. By ‘good luck’ we had a rapid rush of vaccination just before Omicron arrived which made for high protection against Omicron before vaccine protection waned. 
 
Australia was further lucky that when we opened up, Omicron was the circulating virus that was less lethal than (say) Delta.  But this paper makes the important point that even Omicron, in an unvaccinated population, would have had a massive death toll.
 
The estimated deaths averted in this paper are probably underestimates, as higher vaccination rates would have had positive spillover effects of reducing transmission.
 
In future pandemics, we hope that vaccines will be good at BOTH stopping you dying and stopping you transmitting the virus – as this would reduce the health loss even more.  That said, for this pandemic with the vaccines we had, an elimination strategy and delaying opening up until most of us had been vaccinated was (clearly) the least worst option we could have pursued.

It is important that we evaluate all aspects of our pandemic response, and this study contributes to this important task by assessing the impact of the COVID-19 vaccination rollout. Whilst it can’t be ignored that there were missteps, and there are things that could have been done better, it was a significant achievement that in Australia we were able to achieve one of the highest vaccination coverages globally.

This study sought to answer a number of key questions regarding the rollout, including how many deaths were averted due to the vaccination program in Australia. In addition, it sought to estimate how much higher the risk of death was following COVID-19 infection for individuals who remained unvaccinated compared to those who received the vaccine.
 
Without going into the technical aspects of this study, the overall strategy was to use a simple modelling approach to examine these and other questions. Weekly death rate data for those aged 50 years and older in NSW (between August 2021 and July 2022) was used as this jurisdiction had the highest quality data available and was seen to be broadly representative of the national experience.
 
Despite the fact that NSW had the highest quality of data available in Australia, there were limitations of this data and limitations in this study that require that the estimates produced be considered approximations. Importantly, the study authors have been fully transparent about the various limitations of this study and highlight that further work needs to be done when better data becomes available.
 
However, in terms of the questions indicated previously, this evaluation suggests that if there had been no vaccination rollout, approximately (and conservatively) 21,250 deaths would have occurred in NSW, which is some six times higher than the total that was observed over the study period. In addition, it was estimated that unvaccinated individuals had a 7.7-fold greater mortality rate than those who were fully vaccinated, with this mortality rate estimated to be 11.2- times higher when compared to vaccinated individuals who received a booster.
 
These findings are a welcome contribution to the literature and provide supportive evidence for the success of the Australian vaccination rollout.

The rapid development of safe and effective vaccines for COVID-19 is perhaps one of the greatest achievements of medical science. Given the COVID-19 vaccines, like most vaccines in fact, are not 'perfect' in that they do have some limitations including not completely preventing infection in all recipients, and not unexpectedly they have been responsible for some adverse events, many have been critical of them.

Further, a challenge with a successful public health intervention on this scale is given the lack of an obvious control group, sometimes it’s difficult to fully appreciate the magnitude of benefit provided.
 
There have been many studies from other countries already estimating the benefit of vaccination for COVID-19 and have estimated the number of cases prevented to be in the order of 10s to 100s of millions, and deaths prevented to be in the 100s of thousands to many million, many of these estimates for the first year of vaccination alone.
 
This study is particularly useful as it looks at data from Australia, NSW in particular, and given the study period was August 8, 2021, to July 9, 2022, includes the Delta and early Omicron variants. The authors looked at weekly death rates with respect to vaccine status in individuals aged 50 and over, a population where the risk is greater for more severe outcomes.
 
The findings of the study are significant in that it was demonstrated that unvaccinated individuals had a 7.7-fold greater chance of dying from COVID-19 than those who were fully vaccinated (which in this case refers to the two-dose primary vaccination course). The benefit of vaccination was even greater in those boosted, with the reduced chance of dying from COVID-19 being 11.2-fold. The study also looked at what the benefit might have been if the rollout had commenced earlier and found that the additional deaths averted would likely have been small at approximately 440. This is likely explained by the relatively low number of cases and therefore deaths during this period largely due to the public health and social measures in place at the time, and that as a result widespread community transmission had not yet been established. Had there not been a vaccination campaign, this study predicts that a conservative estimate of the number of deaths likely observed over the study period would have been approximately 21,250 instead of the 3495 observed, a difference of around six times.
 
While a really useful study in my opinion to show just how much benefit was likely obtained from the vaccination rollout in this country, like all studies there are some limitations to consider. This study used data from one state only, NSW. It would be great to see a similar study from across the country as the experience with COVID-19 was not the same in all states, however there is not a single source of data that makes a larger study easy to do and NSW is the largest state (approximately 32% of the population of Australia). Modelling studies do not necessarily predict perfectly what would have actually happened, there are additional confounders that are difficult to take into account and the outcome from modelling is only as strong as the data that is put into the model, however in this case the data and methods seem robust. Finally, while relatively recent and therefore including the early Omicron period, the SARS-CoV-2 virus has evolved since the study period and so the situation with COVID-19 has changed. We are now dealing with different subvariants of Omicron to those included in the study and as a result, have seen successive updates to the vaccines available also.
 
Ultimately while it should be clear that the vaccination rollout had a tremendous impact, this study adds useful estimates of the large numbers of lives saved and should help to reinforce the benefits of vaccinating for COVID-19. While the benefits of vaccinating for COVID-19 now are likely to have changed somewhat, it will remain an important part of our strategy for managing COVID-19 for the foreseeable future.