Fact check: Misleading comparison between COVID-19 mortality rate and vaccine efficiency

Social media users have questioned why a COVID-19 vaccine found to be 90% efficient has been hailed as a breakthrough, when the disease itself has a survival rate of 99%. This comparison lacks context.

Reuters Fact Check. REUTERS

“How are people ok with a 90% success rate for the Pfizer #vaccine but yet they’re not ok with a 99% survival rate for the virus? Make it make sense please”, posts shared on online read (here) (here) .

It should firstly be noted that vaccine efficiency and the survival rate are two separate measures, and so are not directly comparable.

The vaccine efficiency is the probability the vaccine will prevent someone from catching COVID-19, while the survival rate is the likelihood that someone who has already contracted the disease will survive.


While the exact mortality rate of COVID-19 is still not known, a hypothetical rate of 1% would still result in a massive number of deaths if left to spread unchecked.

Even with restrictions such as lockdowns, there have been so far been more than 1.3 million COVID-19 deaths recorded worldwide, according to data from Johns Hopkins University ( .

Alongside this, the post does not consider that the impact of COVID-19 extends beyond its death toll.

“Some UK NHS trusts have around 30% of their beds taken up with COVID-19 patients, and there are around 30000 NHS staff off work due to a COVID-19 infection or self-isolating”, Michael Head, senior research fellow in global health at the University of Southampton, told Reuters via email.

“Infection control takes up a huge amount of resource, wards have to be closed, and thus COVID-19 has a massive knock-on effect on other care, such as cancer, mental health or stroke patients”.

There is also the impact of ‘long COVID’, an ongoing illness after contracting the coronavirus, which Head notes has been emerging as a “significant chronic burden” in the young and healthy or those who had a mild initial infection.


Even though no vaccine is 100% effective, this does not make it an ineffective tool for controlling disease and preventing deaths.

Flu vaccines, for instance, are between 40%-60% effective but help save lives. The US Centers for Disease Control and Prevention (CDC) estimated that during the 2018-19 season, the vaccine prevented 3,500 influenza-associated deaths (here) .

Head explains that, at time of writing, there are around 1.5 million confirmed COVID-19 cases in the UK (here) .

“If there had hypothetically been a 90% effective vaccine available at the start of the year, then this would hypothetically reduce expected cases to around 150000”, Head said.

“And going further, assuming a 99% survival and 1% death rate, then this would show 1500 deaths, rather than around 50000.”


Missing context. A 90% efficiency rate for a vaccine would substantially reduce the spread and death toll from COVID-19. A 1% mortality rate, on the other hand, would still lead to a massive number of deaths if the disease was left to spread unchecked.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts here .