Vaccine protection wanes three months after second dose

A new study published in the journal The Lancet has found that the protection offered by the Oxford-Astra Zeneca Covid-19 vaccine starts waning considerably three months after receiving the second dose. These findings – drawn from the analysis of large datasets from Scotland and Brazil – suggest that booster doses are needed to help maintain protection against severe disease in people vaccinated with Oxford-Astra Zeneca.

 “Our analyses of national datasets from both Scotland and Brazil suggest that there is considerable waning of effectiveness for the Oxford AstraZeneca vaccine, with protection against severe Covid-19 falling over time,” reported study lead author Vittal Katikireddi, a professor of Public Health at the University of Glasgow. 

“We studied two million people in Scotland and over 42 million people in Brazil who had received two doses of the Oxford-AstraZeneca vaccine. More than four months after receiving a second dose, the risk of experiencing either a Covid-19 hospitalization or death was approximately five times greater than the period of maximum vaccine protection after accounting for changes in infection rates and a range of other factors.”

Since both Scotland and Brazil had a similar interval between vaccine doses (12 weeks) and similar initial prioritization of who was vaccinated (healthcare workers and people at high risk of developing severe illness), the scientists have been able to reliably compare the findings. In both countries, the decline in effectiveness began to appear three months after the second dose, with the risk of hospitalization and death increasing threefold before four months and fivefold soon after.

“Vaccines have been a key tool in fighting the pandemic, but waning in their effectiveness has been a concern for a while,” said study co-author Aziz Sheikh, the director of University of Edinburgh’s Usher Institute. 

“By identifying when waning first starts to occur in the Oxford-Astra Zeneca vaccine, it should be possible for governments to design booster programs that can ensure maximum protection is maintained.”

“If eligible for a booster and you have not had yet had one, I would highly recommend that you book one soon,” Dr. Aziz urged.

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By Andrei Ionescu, Earth.com Staff Writer