A rise in vaccinated people becoming infected with coronavirus has cast doubt over the lasting efficacy of Covid-19 vaccines, according to new studies, including one that found protection gained from the BioNTech/Pfizer shot declined more rapidly than that from the AstraZeneca jab.
An Oxford university study published on Thursday found that the efficacy of the Pfizer vaccine against symptomatic infection almost halved after four months, and that vaccinated people infected with the more infectious Delta variant had as high viral loads as the unvaccinated.
Two research papers from the US and Qatar have also fuelled debate over the need for top-up booster shots as they found higher numbers of “breakthrough infections” than anticipated, even though protection against serious cases of the virus appears to hold.