People who have had the Pfizer vaccine have lower antibody levels targeting the coronavirus variant first discovered in India than those against previously circulating variants in the UK, new data suggests.
The research also suggests the levels of these antibodies are lower with increasing age and that levels decline over time.
Researchers say this provides additional evidence in support of plans to deliver a vaccination boost to vulnerable people in the autumn.
The study found after one dose of the Pfizer jab, people are less likely to develop antibody levels against B.1.617.2, also known as Delta, as high as those seen against the previously dominant B.1.1.7, also known as Alpha.
However, levels of antibodies alone do not predict vaccine effectiveness and prospective population studies are also needed. Lower neutralising antibody levels may still be associated with protection against Covid-19, the experts say.
The Delta variant is now believed to be dominant in the UK, with early evidence suggesting it may lead to an increased risk of being admitted to hospital compared with the Kent variant.
A total of 12,431 cases of the mutation have been confirmed in the UK up to June 2, according to Public Health England. This up 79% from the previous week’s total of 6,959.
Emma Wall, UCLH Infectious Diseases consultant and senior clinical research fellow for the study, said: “This virus will likely be around for some time to come, so we need to remain agile and vigilant.
“The most important thing is to ensure that vaccine protection remains high enough to keep as many people out of hospital as possible.
“And our results suggest that the best way to do this is to quickly deliver second doses and provide boosters to those whose immunity may not be high enough against these new variants.”
The study was led by the Crick and partners at UCL and University College London Hospitals NHS Foundation Trust (UCLH). Healthcare workers and staff have been donating regular blood and swab samples so researchers can track the changing risk of infection and response to vaccination.
Within days of having enough of each variant to study, researchers analysed antibodies in the blood of 250 healthy people who received either one or two doses of the Pfizer vaccine, up to three months after their first dose.
They tested the ability of antibodies to block entry of the virus into cells, so called neutralising antibodies against five different variants – the original strain from China, the dominant strain in Europe during the first wave in April 2020, and the variants first detected in Kent, South Africa and India.
Data from previous studies suggests that higher antibody titres – the greatest dilution level that still blocks 50% of virus infection in the lab – is a good predictor of vaccine efficacy and greater protection against Covid-19.
According to the research, in people who had received two doses of the Pfizer/BioNTech vaccine, levels of neutralising antibodies were more than five times lower against the Indian variant when compared to the original strain, upon which current vaccines are based. This antibody response was even lower in people who had only received one dose.
After a single dose of the Pfizer jab, 79% of people had a quantifiable neutralising antibody response against the original strain, but this fell to 50% for B.1.1.7, 32% for B.1.617.2 and 25% for B.1.351 (South Africa).
Eleanor Riley, professor of immunology and infectious disease, University of Edinburgh, said: “These data cannot tell us whether the vaccine will be any less effective at preventing severe disease, hospitalisation and death; we need to wait for the actual data on these outcomes.”