The Pfizer Covid-19 vaccine looks to offer 100% protection against the South African variant, and is mostly likely highly effective against the variant that originated in Brazil, two new studies suggest.
In the first in-human evidence of how the vaccine protects against variants, research published by Pfizer/BioNTech on Thursday showed the vaccine is 100% effective in preventing Covid-19 cases in South Africa – where the South African variant is now common.
The research was part of a larger, phase three clinical trial also showing the vaccine was highly effective even after six months.
It comes as a separate UK-based study found the Pfizer vaccine produces an “off the scale” immune response that is likely to protect against the Brazilian variant of Covid-19, with scientists in the UK reporting strong immune responses in older people who had received two shots of the Pfizer vaccine.
The South African study among 800 people in South Africa, nine cases of the South African variant of Covid were observed – all in the group not given the vaccine.
Of the nine people who fell ill, analysis showed they had six of nine known South African variant strains.
A second study, the largest 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 Pfizer jab.
Responding to the first study, the pharmaceutical giant said the data supports “previous results from immunogenicity studies demonstrating that (the vaccine) induced a robust neutralising antibody response to the (South African) variant”.
Professor Peter Openshaw, from Imperial College London, welcomed the study but pointed to the low number of coronavirus cases that occurred in the South African arm of the trial.
“It might be 100% effective, but as more data accumulates it is possible that cases will appear that show a lower protection rate,” he said.
He added that the study looked at severe disease but “it seems likely” that the jab “will reduce less severe types of infection as well”.
Meanwhile, 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.
Some 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.
A preprint with The Lancet, the research found those people who 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 in the UK trial 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 he was surprised how well the vaccines have worked in older people.
"When we sent these samples to Porton Down they said ‘we can’t give you results right now because we’ve got to dilute them because they’re so high, they’re off the scale’.
“The antibody levels were so high that they’d gone above the thresholds so they had to dilute them.”
But he added it will be crucial to see how long antibody levels are maintained after people have had a Covid-19 vaccine.
“It will be important to assess that and whether they wane at different rates in people of different ages,” he said.
Although the new study did not look at the Oxford University/AstraZeneca vaccine, Prof Moss said the evidence for the jab is that “it’s very, very effective”.
Prof Moss said the UK’s plan to exit lockdown appears to be “on track”, with policies to control variants, the development of new vaccines and a strong immunisation programme.
“I think we can be confident about gaining control of variants with the current plans, and also leaving lockdown,” he said.
First author on the paper, Dr Helen Parry, a National Institute for Health Research academic clinical lecturer at the University of Birmingham, said: “Our research provides further evidence that the mRNA vaccine platform delivers a strong immune antibody response in people up to 96 years of age and retains broad efficacy against the P.1 (Brazilian) variant, which is a variant of concern.”