Study estimates that the Covid-19 vaccines saved 15 million lives last year

In a new study published in the Lancet, Watson et al. estimate that by the end of 2021, the Covid-19 vaccines have prevented an estimated 14.4 million deaths (with a 95% credible interval of between 13.7- 15.9 million deaths) .

The estimate would rise to 19.8 million (19.1 – 20.4 million 95% CrI) if they used excess deaths as opposed to deaths specifically reported as being due to Covid – which in many cases are regarded as more reliable figures.

Figure 1 from the study: Global COVID-19 deaths averted due to vaccination based on excess mortality

By necessity these estimates are based on a mathematical model using the best data the researchers could find, rather than them having discovered an actual parallel universe that had no vaccines to measure against. But, at a glance, it looks like a pretty sophisticated and thoughtful model, building on past work. They make the details available in a supplementary appendix.

In summary, they adapt a previously published SEIR model, wherein people move through Susceptible, Exposed , Infected and Recovered states. Some of the variables taken into account include the age structure of the population, disease severity and transmission dynamics, people moving through different healthcare levels (allowing modelling of the need for intensive care for instance), immunity due to infection, immunity waning effects as well as how the vaccines were rolled out. The differing efficacy of the specific vaccines used is incorporated whilst they model effectiveness against infection, against severe disease and in lowering infectiousness. The flow of the Covid variants are also incorporated where possible.

This is all great news, and it’s good to have something to celebrate about 2021! However the study does also highlight a less wholly positive outcome.

When one looks at the map of lives saved per capita, it’s obviously that richer countries got far greater benefit from the vaccines than the poorer ones.

Figure 2 from the study: Median deaths averted by vaccinations per 10 000 people by country in the first year of COVID-19 vaccination

That’s not hard to explain. To quote a BBC news story from the end of 2020:

The People’s Vaccine Alliance says nearly 70 lower-income countries will only be able to vaccinate one in 10 people.

Their analysis found that rich countries have bought enough doses to vaccinate their entire populations three times over if all the vaccines are approved for use.

Canada, for example, has ordered enough vaccines to protect each Canadian five times, it claims.

And even though rich nations represent just 14% of the world’s population, they have bought up 53% of the most promising vaccines so far,

The rich countries simply hoarded the lion’s share of particularly the more effective mRNA vaccines for themselves, in some cases more doses than they could ever use before they expired.

The researchers estimate that had the COVAX commitment to a minimum of 20% vaccine coverage within the lower and middle income countries covered by its Advance Market Commitment by the end of 2021 actually been met, then around a further 160,000 deaths may have been prevented

And if all countries been able to meet the WHO target of 40% vaccination coverage by the end of 2021 then that increases to around 600,000 extra lives that could have been saved.

One important caveat to note, apart from some inevitable inherent uncertainty in some of the data sources involved and modelling choices made, is that the counter-factual here is “a world that behaved the same as our one but had no access to vaccines”.

Of course it may have been the case that in the absence of vaccines then some countries may have focussed harder on other preventative measures, such as lockdowns, which may have reduced the difference in lives lost. But, let’s be honest, that’s far from certain given the lack of political enthusiasm for these measures in some quarters even in pre-vaccine times.

Either way, even if the estimate was out by millions, it’s clear that Covid vaccines have been one of the most astonishingly effective feats of science and medicine in recent times in terms of that most critical of outcomes, saving lives. But also one that by the virtue of how it was implemented tended to exacerbate existing inequity.

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