Pfizer jab stands up well against variants
Data shows vaccine can prevent severe cases in infections caused by two strains of the virus
The Pfizer-BioNTech vaccine appears able to prevent severe cases of Covid-19 caused by two variants of the coronavirus, but is less effective at blocking infection entirely from one of the new strains in circulation, according to new real-world data from Qatar.
The results, published in a letter to The New England Journal of Medicine, come as scientists around the world race to understand how well Covid-19 jabs will work against the mutated strains which have emerged since the vaccines were designed.
Scientists supported by Qatar’s public health ministry conducted the analysis as two more transmissible strains of the virus were gaining a foothold in the country – the variant known as B.1.1.7, first identified in Britain, and B.1.351, in South Africa.
The results showed the PfizerBioNTech vaccine’s effectiveness against severe or fatal cases of Covid-19 was very high – at 97.4 per cent – at a time when both strains were dominant. When it came to protecting against any documented infection from the B.1.351 variant, it was found to be just 75 per cent effective – roughly 20 percentage points lower than previous results which were not specific to this strain.
In clinical trials conducted before the variants began circulating, the Pfizer dose was found to be 95 per cent effective in preventing Covid-19. These findings were supported by a real-world study in Israel.
Several studies have pointed to the potential for B.1.351, which contains a mutation to the part of the virus targeted by vaccines, to affect how well the jabs work.
Doses by Johnson & Johnson and AstraZeneca were found to be less effective against mild and moderate Covid-19 in clinical trials in South Africa, where the variant was spreading, compared with those run at other trial sites. But there was a minimal difference when it came to protecting against severe disease for the Johnson & Johnson vaccine. Similar data was not available for AstraZeneca.
The Qatar data appears to support expectations that protection against severe cases or death would remain high against variants of the virus, even if efficacy for all infections was affected.
“The reduced protection against infection with the B.1.351 variant did not seem to translate into poor protection against the most severe forms of infection [such as] those resulting in hospitalisation or death, which was robust,” the researchers wrote.