An independent analysis conducted by Public Health England (PHE) in the UK demonstrates that the Pfizer-BioNTech COVID-19 vaccine BNT162b2 provides protection against infection and asymptomatic disease after the first dose.
BNT162b2 reduces risk of SARS-CoV-2 infection by 70% after one dose
The UK's vaccination program began on December 8 when BNT162b2 became the first COVID-19 vaccine to receive emergency authorization, shortly followed by the Oxford-AstraZeneca vaccine ChAdOX-1 was added to the program.
In a prospective research study known as the SIREN study, PHE are monitoring COVID-19 effectiveness in health care staff working in England. In the study, baseline risk factors, vaccination status and symptoms are recorded at two-week intervals and SARS-CoV-2 PCR and antibody test results are analyzed.
The data shared by PHE relates only to the Pfizer-BioNTech COVID-19 vaccine, not the Oxford-AstraZeneca vaccine. "The emergency use authorisation came through later, for the latter, however, which might explain why this early data relates only to the Pfizer-BioNTech vaccine," Dr Peter English, consultant in communicable disease control and immediate past chair of the BMA Public Health Medicine Committee, said.
The data shows that the risk of being infected by SARS-CoV-2 is reduced by 70% after one dose of the Pfizer-BioNTech vaccine, and by 85% after a second dose.
"This adds to the data on infection from the recent Lancet letter from Israel, showing a reduction in infection in healthcare workers," said English. Healthcare workers in the UK have been systematically tested for COVID-19, making it more likely that an asymptomatic infection would be detected. "It’s not clear how they detected asymptomatic infections, the UK data is more useful," English said.
Data for populations aged 80 and over
The research data suggests that vaccine effectiveness in over 80-year-olds is initially lower; it is 57% effective against symptomatic COVID-19 disease 28 days after the first dose, increasing to 88% seven days after the second dose. English said that this finding is unsurprising, as immunosenescence can reduce vaccine efficacy in older populations. Nonetheless, BNT162b2 appears to reduce the likelihood of hospitalization by ~40% and the risk of death is less than half in vaccinated individuals compared to those that have not been vaccinated.
"This is strong evidence that the Pfizer-BioNTech vaccine is stopping people from getting infected, while also protecting cases against hospitalisation and death. We will see much more data over the coming weeks and months but we should be very encouraged by these initial findings," – Dr Mary Ramsay, head of immunization at PHE, in a press release.
Achieving herd immunity
English emphasized that if we are to achieve herd immunity via vaccination, then vaccination must prevent both infection and transmission. "These early data from this and the Israel studies are the first to demonstrate real-world reductions in infection, which mean likely reductions in transmission," he said.
These reported findings are based on preliminary data and PHE states that it will continue to observe trends closely over the coming months to ensure that firmer conclusions can be made. Real-world data on the impact of the Oxford-AstraZeneca vaccine is expected to follow in due course, PHE said: "Early signals in the data suggest it’s providing good levels of protection from the first dose."