A large British study showed that the effectiveness of the Pfizer and AstraZeneca vaccines diminishes over time. 90 days after the second shot, the AstraZeneca vaccine is still 61% effective against infection with the coronavirus. The Pfizer vaccine is still 75% effective at that time.
This is the conclusion of researchers at Oxford University who examined more than three million swabs from the nose and throat. The effectiveness of the injection decreases over time, with previous research results showing that the AstraZeneca vaccine is 68 percent effective two weeks after the second shot. The Pfizer vaccine is 85% effective at that point.
The researchers concluded that efficacy declines more rapidly in vaccines over the age of 35 than in young adults. However, researchers say vaccination is still a wise choice. “Both vaccines are still working very well,” said lead researcher Sarah Walker. “If you start too big (in terms of potency, editor), you still have a long way to go.”
The delta variant also reduces the effectiveness of vaccines. The researchers concluded that after infection with the delta variant, vaccinated people had as many virus particles in their nose and throat as unvaccinated people. “This can make herd immunity more difficult,” explains Dutch researcher Koen Boels. “Vaccines are probably best at preventing severe disease, but are slightly less effective at preventing transmission of the virus.”
As a side note, the researchers note that the number of virus particles in the throat is only a “rough indication” of the severity of symptoms. There is no new information about the duration of the infection. The study has not yet appeared in a medical journal and must be peer reviewed before publication.