The Pfizer vaccine produces an “off the scale” immune response that is likely to protect against the Brazilian variant of Covid-19, researchers say.
The biggest study on antibody and cellular immune factors to date suggests people are likely to be protected against the Wuhan, Kent and Brazilian types of coronavirus following two doses of the vaccine.
The research, led by the University of Birmingham and including Public Health England’s Porton Down laboratory, found 98% of people aged 80 or over who had two doses of the Pfizer jab had a strong antibody immune response.
It comes as other new data from Pfizer suggests the vaccine is 100% effective in preventing Covid-19 cases in South Africa, where the variant which emerged in that country is common.
Among 800 people in the South African arm of a phase three clinical trial, nine cases of Covid-19 were observed – all in the group not given the vaccine.
Six of the nine Covid cases were the South African strain, with Pfizer saying this demonstrates the jab can induce “a robust neutralising antibody response to the (South African) variant”.
For the Birmingham study, 100 people aged 80 to 96 received their vaccine doses three weeks apart, before the UK adopted a policy of stretching the time between jabs to 12 weeks.
Published in The Lancet, the research found people who had previously had natural Covid-19 infection had a peak antibody response after just one Pfizer vaccination.
The antibody response in these people remained 28-fold higher even after the second vaccine dose.
Blood samples from all participants showed the original Wuhan strain was strongly neutralised after two doses of the jab.
While neutralisation reduced 14-fold when tested against the Brazilian variant, experts believe the very high immune response generated by the vaccine is enough to provide protection against that strain.
The study found cellular T cell responses developed in 63% of the older people given two doses of the Pfizer jab.
Like the cells which produce antibodies, T cells are crucial to the immune system’s response to viral infection.
Professor Paul Moss, from the University of Birmingham and leader of the UK Coronavirus Immunology Consortium, told a briefing: “In terms of the variants and how we control them, people seem to be taking two broad approaches.
“One is we can develop another vaccine, a booster against these specific variants, so we perhaps have a South African booster vaccine – that’s one approach and people are working on that.