People who have had the Pfizer vaccine have lower antibody levels that specifically target the Delta variant than those against other 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: “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.
A previous study has shown the Pfizer and AstraZeneca coronavirus vaccines are effective against the Delta variant after two doses. Public Health England, who ran the study, said the vaccines are likely to be even more effective at preventing hospital admission and deaths. Both vaccines were only 33% effective against the Delta variant three weeks after the first dose.
At the time, Matt Hancock said the findings made him “increasingly confident” the final stage of easing restrictions in England could take place on June 21.
A separate study from May 2021 found “most” UK adults had some form of antibodies after one dose of AstraZeneca or Pfizer. Researchers found 96.42% of people who had either vaccine had developed antibodies 28 to 34 days after their first dose, rising to 99.08% within seven to 14 days of the second dose.
The Crick study on antibodies that specifically target the Delta variant doesn’t necessarily mean the vaccine is less effective, as antibodies alone do not predict vaccine effectiveness. But it could increase the risk of vaccines being less effective, and highlights the importance of second and booster jabs.