Vaccine efficacy: beyond the average

Australian experts are debating about the efficacy of AstraZeneca vaccine. Some argue that the efficacy (VE) of the vaccine is not good enough for herd immunity; others say that it is better than … face mask. I think the debate has been misled by the heavy reliance on the average. In this note, I want to make 3 comments on the true value of VE and its implication for herd immunity.

Australia is about to implement a COVID-19 vaccine program, with Oxford/AstraZeneca vaccine being the intervention of choice. It is expected that up to 80,000 people will be vaccinated by week 4, and 4 million by the end of March 2021. It is going to be a major public health effort.

However, some experts (eg immunologists and infectious disease specialists) are calling for a rethink of the program. They quoted the vaccine efficacy of 62% and argued that such a degree of efficacy is not high enough to achieve herd immunity [1].

Other experts, including the Government’s Chief Medical Office (CMO), argue that the vaccine efficacy is good enough. An expert quoted the efficacy of ‘up to 70%’ and said that was a great news. He reminds us that the efficacy of mask wearing was only 15–20% [1]. The CMO went on to advise that we should listen to the experts, because “they are hand picked experts on these matters”.

Which vaccine efficacy?

Well, in science we have the saying, “In God we trust, all else bring data”. Surely, experts’ opinions are important, but scientifically their…