The protection that the Oxford-Astra Zeneca vaccine can offer starts to decline after three months of receiving the second dose, according to a study published in The Lancet (1). Data from both Scotland and Brazil show that booster programmes are essential to maintain protection in people vaccinated with the Oxford-Astra Zeneca vaccine.
This study is part of the EAVE II project, which uses anonymised patients to track the pandemic in real-time.
A team of researchers from several universities in Scotland and Brazil analysed results from two million people in Scotland and 42 million people in Brazil who received the Oxford-Astra Zeneca vaccine. Data showed a fivefold increase in the chance of being hospitalised with Covid-19 about five months after vaccination. In fact, the decline started at around three months, when the risk of severe illness and death doubled compared to two weeks after the second dose.
“Vaccines have been a key tool in fighting the pandemic, but waning in their effectiveness has been a concern for a while,” said Professor Aziz Sheikh, Director of the University of Edinburgh’s Usher Institute and EAVE II study lead. “By identifying when waning first starts to occur in the Oxford-Astra Zeneca vaccine, it should be possible for governments to design booster programmes 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.”
Curiously, despite the similar results between the two countries, the dominant variant in each country was different – Delta variant in Scotland and Gamma variant in Brazil. This means the drop in protection is unlikely to be caused by which variant people are infected with.
“This research is a great example of what can be achieved through global collaboration when it comes to the use of data for health research. By drawing on findings from data sets in two countries with differing dominant COVID-19 variants, the researchers have been able to disentangle vaccine waning from the effects of changes in variants – strengthening the evidence for the ongoing booster programme,” said Professor Andrew Morris, Director of Health Data Research UK. “Health Data Research UK is pleased to have been able to support both the development of these data sets and their harmonised analysis, as part of our mission to enable global and trustworthy sharing of data to allow major COVID-19 research questions to be addressed at pace.”
(1) Katikireddi S, Cerqueira-Silva T, Vasileiou E, Robertson C, Amele S, Pan J (2021) Two-dose ChAdOx1 nCoV-19 vaccine protection against COVID-19 hospital admissions and deaths over time: a retrospective, population-based cohort study in Scotland and Brazil. The Lancet, https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)02754-9/fulltext