- Michelle Roberts
- Health Publisher, BBC News Online
Researchers say they see a decrease in protection from Covid-19 infection in people who have received two doses of the vaccine.
A UK study using real data examined positive PCR results between May and July 2021 in more than 1 million people who received two doses of either Pfizer or AstraZeneca.
Protection after two doses of Pfizer increased from 88% in one month to 74% in five to six months. For AstraZeneca, the drop fell 77% to 67% within four to five months.
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Although there have been cases of infection in people who have been fully vaccinated, vaccines still do a good job of protecting the population from the severe form of disease and deaths caused by Covid-19.
Vaccines save lives
Public Health England, the UK government’s public health agency, estimates that around 84,600 deaths and 23 million infections have been prevented thanks to the Covid-19 vaccination campaign in England so far.
Professor Tim Spector of King’s College London (KCL), who led the study based on data from epidemiological research app Zoe Covid, says these findings could explain recent infections reported by some fully vaccinated people.
“The reduction in protection is expected and is not a reason not to vaccinate,” he said.
“Vaccines still provide high levels of protection for most of the population, particularly against the delta variant, so we still need as many people as possible to be fully immunized,” he says.
He estimates that protection against infection can drop as low as 50% in winter and that booster doses are needed – but other experts are urging caution in forecasting the coming months.
The UK is expected to start providing a third booster dose of the Covid vaccine to some people next month, but the government is awaiting recommendations from an independent advisory body called the JCVI, which is reviewing evidence to support that decision.
“A lot of people may not need it,” Spector says. “Maybe a lot of people were naturally boosted because they had a natural infection with Covid before, so in fact they would have had three vaccinations.”
“So I think the whole should be managed with much more care than if we were content to give (the third dose) to everyone, which would be a huge waste and would be ethically questionable given the resources we have. I think we need a more focused approach than last time” .
Simon Clarke, an expert in cellular microbiology at the University of Reading, UK, explains that levels of infection in a community would alter the likelihood that a person would cross (the virus) and contract the virus at some point, making it difficult to paint a definitive picture. Conclusions about the deterioration of immunity.
Alexander Edwards, also of the University of Reading, says it’s important to understand when and for whom booster doses may be needed.
“Vaccination does not put people at risk or prevent all infections. The variables are having a real and significant impact on public health, and tragically many people continue to die in the UK from this horrific virus.”
“The vaccines we have are remarkably safe and effective, and are still much better than other vaccines that offer tremendous benefits.”
“We need to proactively plan our public health strategy to account for incomplete protection and the potential for diminishing protection over time,” he continues.
A similar study was released by the Office for National Statistics and the Oxford Vaccine Group last week.
Based on the results of PCR examination of nearly 400,000 people with the delta variant in the UK, it showed that two doses of the Pfizer vaccine were initially 90% more effective against symptomatic Covid infection, compared to about 70% for the AstraZeneca vaccine.
But over the course of three months, Pfizer’s protection decreased significantly, while AstraZeneca’s immunity remained more stable.
Professor Adam Fane, a government vaccine consultant, explains that other studies have shown that vaccines maintain good protection against serious illness and hospitalization.
But, he says, “we have to be very careful to see if this reduction (for vaccination) compared to mild disease starts to show up in more serious cases, because then the booster doses would be necessary.”
At the moment, there is still no definition for a booster vaccine in Brazil, but both the Ministry of Health and the Butantan Institute (which are responsible for finalizing CoronaVac production in the country) acknowledge that they are evaluating and considering this possibility.
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