Covid: Pfizer vaccine produces low level of antibodies against Delta variant, study shows

Pfizer vaccine recipients have lower antibodies targeting the Delta variant. Credit: PA

People who have received the Pfizer vaccine have lower antibody levels that target the Delta variant, first discovered in India, than those that targeted previously circulating variants in the UK, new data suggests.

The study found that after just one dose of the Pfizer jab, people are less likely to develop antibody levels against the Delta variant, as high as those seen against the previously dominant Alpha variant, which was first discovered in Kent.

The study, from the Francis Crick Institute and the National Institute for Health Research, suggests the level of such antibodies are lower with older age and that the levels decline over time.

It is believed that this research provides additional evidence in support of a vaccination boost to vulnerable people in the autumn.

The new laboratory data also supports current plans to reduce the dose gap between vaccines.

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Emma Wall, UCLH Infectious Diseases consultant and senior clinical research fellow for the Legacy study, said: “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.”

A member of medical staff prepares a Pfizer Covid-19 vaccine. Credit: PA

According to the research, in people who had received two doses of the Pfizer 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 the Alpha variant and 32% for the Delta variant.

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 Alpha 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 figure is up by 79% from the previous week’s total of 6,959.

Confirmed cases of the Delta variant in England.

Researchers conducted the largest study published to date investigating vaccine-induced antibody neutralising capacity against the newest variants of concern in healthy adults.

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.

David LV Bauer, group leader of the Crick’s RNA Virus Replication Laboratory and member of the G2P-UK National Virology Consortium, said: “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.”