People who have had the Pfizer/BioNTech 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 new laboratory data from the Francis Crick Institute and the National Institute for Health Research (NIHR) UCLH Biomedical Research Centre also supports current plans to reduce the dose gap between vaccines.
The study found that after just one dose of the Pfizer jab, people are less likely to develop antibody levels against the Indian (B.1.617.2) variant, also known as Delta, as high as those seen against the previously dominant Kent variant (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 Indian 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 Legacy study, said: “This virus will likely be around for some time to come, so we need to remain agile and vigilant.
“Our study is designed to be responsive to shifts in the pandemic so that we can quickly provide evidence on changing risk and protection.
“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.”
This is the largest study published to date investigating vaccine-induced antibody neutralising capacity against the newest variants of concern in healthy adults.
Researchers have submitted their findings to the Genotype-to-Phenotype National Virology Consortium (G2P-UK), the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) and the Joint Committee on Vaccination and Immunisation (JCVI).
The Legacy study is led by the Crick and partners at UCL and University College London Hospitals NHS Foundation Trust (UCLH).
Healthcare workers and staff from the institutions 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).
David LV Bauer, group leader of the Crick’s RNA Virus Replication Laboratory and member of the G2P-UK National Virology Consortium, said: “New variants occur naturally and those that have an advantage will spread.
“We now have the ability to quickly adapt our vaccination strategies to maximise protection where we know people are most vulnerable.
“Keeping track of these evolutionary changes is essential for us to retain control over the pandemic and return to normality.”
The Research Letter published in The Lancet states: “These data, together with epidemiological data of B.1.617.2 growth, raise the possibility that this VOC (variant of concern) presents a dual challenge of reduced vaccine efficacy akin to the B.1.351 VOC, and increased transmissibility beyond the B.1.1.7 VOC.”
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.”