The Pfizer-BioNTech Covid-19 vaccine elicits an “off-the-scale” immune response, British researchers said on Thursday after a real-world study of the drug.
The research showed the vaccine was likely to protect against strains of the virus first identified in Brazil and south-east England.
The study, by the University of Birmingham and Public Health England, found 98 per cent of people aged 80 to 96 who had two doses showed a strong antibody immune response.
One hundred elderly people received doses three weeks apart, before the medical regulator extended the time between doses to 12 weeks.
Researchers said those who had previously been infected with the coronavirus showed a peak antibody response after one dose of the vaccine.
Blood samples showed strong protection against the original variant first identified in Wuhan, China, although the vaccine's effectiveness dropped 14-fold when tested against the Brazilian strain.
But Prof Paul Moss from Birmingham University said he was confident Pfizer-BioNTech’s vaccine “retains broad efficacy" against the Brazilian variant.
He said the results of the study were reassuring, particularly since the antibody response was strong even in the oldest participants, aged 96.
“We’ve certainly seen in this paper that the antibody levels are so good, after the first two weeks, that we are confident that this should be helpful against the Brazilian variant,” he said.
Asked whether he was surprised at how well the vaccines worked on older people, he said he was.
Prof Moss said the samples were sent to Porton Down, the UK’s centre for researching dangerous pathogens, whose scientists told him they were unable to “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,” he said.
Immunity measurements were taken two weeks after the second dose, the researchers said. The results have not been peer-reviewed by other scientists.
Prof Moss said the UK’s lockdown exit plan remained on track, largely because of the inoculation campaign, but he said it was necessary to observe how long antibody levels were maintained after vaccination.
“I think we can be confident about gaining control of variants with the current plans,” he said.
A separate Pfizer-BioNTech study released on Thursday suggested the vaccine was highly effective in preventing Covid-19 cases in South Africa, where another virulent variant of the virus was identified.
It found no coronavirus cases were observed in the country during a phase-three clinical study among participants who had received their second dose.
Among the 800 participants, nine Covid-19 cases were identified – all in the group given a placebo. Six of the nine cases involved the South African variant.
Pfizer chief executive Albert Bourla said the study “provides further confidence in our vaccine's overall effectiveness”.