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Careful planning needed to counter release of weakly effective COVID-19 vaccine

The world needs efficient, speedy, and reliable evaluation of COVID-19 vaccine candidates, according to a recent article in the Lancet, but careful planning must be in place to counter the danger that political and economic pressures might lead to release of a weakly effective COVID-19 vaccine, a situation that could potentially worsen the pandemic.

Thomas Fleming
Thomas R. Fleming

Written by members of the World Health Organization (WHO) Solidarity Vaccines Trial Expert Group including Thomas R. Fleming, a professor of biostatistics with the University of Washington School of Public Health, the article outlines three critical areas of COVID-19 vaccine trial planning that, if followed, will prevent distribution of a weak vaccine.

To begin, a vaccine candidate should be evaluated based on evidence of worthwhile efficacy, not just some efficacy.  WHO recommends that successful vaccines reduce estimated risk by at least 50%, with true efficacy greater than 30%. However, it is possible for a vaccine to demonstrate 50% reduced risk in the short term, and yet experience a wane in effectiveness over time. If such a vaccine were distributed, health officials could wrongly assume the risk of COVID-19 transmission has been meaningfully reduced, and individuals who received the vaccine could wrongly believe they are immune and stop implementing other preventative measures such as wearing a mask and social distancing. 

There is also a matter of efficiency; prioritizing not only single vaccine trials but also multiple vaccine trials. The WHO Solidarity Vaccines Trial introduces efficiency through measures such as permitting selected vaccines from geographically diverse sites to enter the trial whenever they are ready, evaluating multiple vaccines with a shared control group, and utilizing a flexible mix of fixed and pop-up sites to enroll large numbers of participants at sites with high rates of COVID-19.

Finally, a trial should take a longer-term view toward vaccine efficacy and safety. The WHO will continue active follow-up of vaccine and placebo groups after demonstration of short-term efficacy but before an effective vaccine has been deployed in local populations.

More than 250 research sites are expected to join the WHO Solidarity Vaccines Trial. “Our goal is to efficiently provide timely and reliable evidence of efficacy and safety to support regulatory and political decision-making about global COVID-19 vaccine deployment of multiple safe and effective vaccines, with equity of access internationally,” says Fleming.

Other UW members of the WHO Solidarity Vaccines Trial Expert Group include Peter Gilbert (Biostat), Elizabeth ‘Betz” Halloran (Biostat), Yunda Huang (Global Health), and Holly E. Janes (Biostat).

Outline of WHO Solidarity Vaccines Trial Goals & Strategies


Deb Nelson, UW Biostatistics Communications