Researchers have found that those double vaccinated against Covid-19 could see immunity waning within six months of innoculation.
The Zoe Covid Study launched an app feature in December 2020 to log Covid-19 vaccines and monitor real-world side-effects and effectiveness in its more than a million active users.
It found that the protection provided by two doses of the Pfizer/BioNTech and the Oxford/AstraZeneca coronavirus vaccines starts to wane within six months.
The Pfizer jab was 88% effective at preventing Covid-19 infection a month after the second dose. But after five to six months, the protection decreased to 74%, suggesting protection fell by 14% in four months.
With the AstraZeneca vaccine, there was a protection against infection of 77% one month after the second dose. After four to five months protection decreased to 67%.
The study drew on more than 1.2 million test results and participants.
The mid-term efficacy trial by Pfizer observed an initial 96.2% risk reduction in infection (up to two months after the second dose). There was an 83.7% reduction more than four months after the second dose.
Should you be worried?
The results are not too alarming as experts expect real-world analysis to show less protection than clinical trials – and the vaccines are still hugely effective in reducing serious side effects and death from the virus. So health professionals do universally encourage getting vaccinated.
“Waning protection is to be expected and is not a reason to not get vaccinated,” says Professor Tim Spector, lead scientist on the Zoe Covid Study app. “Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to get fully vaccinated.”
Dr Alexander Edwards, a professor in biomedical technology at the University of Reading, adds: “Vaccination does not (unsurprisingly) make people invulnerable, and does not prevent all infections. Variants have real and significant impact on public health, and a lot of people are still tragically dying in the UK from this nasty virus.
“The vaccines we have are remarkably safe and effective, and still remain far better than other vaccines that give massive benefits. We must pro-actively plan our public health strategy to account for imperfect protection, and for the possibility of falling protection over time.”
What does it mean for booster shots?
The NHS is planning to roll out a Covid-19 booster programme from September, giving those most at risk from coronavirus extra protection ahead of winter.
Final plans for the booster programme, which is likely to start in September, will be confirmed once results from clinical trials are available. But these are set to be available for those aged 70+, those in care homes, and people whose immune systems aren’t working properly.
The jury is still out for large-scale booster shot roll-outs as it is logistically harder to mix and match vaccines to booster shots.
What does it mean for Covid variants?
The current vaccines offer protection against the coronavirus infections that were circulating when the vaccines were being developed and trialled, and so don’t specifically target the variants that have come since, such as Delta.
Dr Julian Tang, a professor and clinical virologist at the University of Leicester, explains: “We know already from lab studies that the Delta variant can escape vaccine and natural protection when antibody levels start to fall below a certain level – to cause infection. This is not so surprising as the current generation of Covid vaccines were designed against the original Wuhan virus variant.”
“Whilst booster shots with the current generation of vaccines designed against the original Wuhan virus will boost levels of cross/reacting antibodies, overall, they will not be very effective against the Delta variant as they are not specific for this virus. So once the antibody levels drop again, the Delta variant will break through.”
Optimum protection will only be achieved when vaccines are designed for specific viruses, “as we try to do against seasonal flu each year”, he adds – but these take time to design, manufacture and distribute. “Vaccines will always be playing catch-up. We really need to develop updated vaccines against the Delta virus, specifically, to maintain longer-lasting, specific immunity to this variant.”