The study also shows that levels of these antibodies that are able to recognise and fight the virus are lower with increasing age, and that levels decline over time, providing additional evidence in support of plans to deliver a booster dose to vulnerable people.

It supports current plans in the UK to reduce the dose gap between vaccines since they found that after just one dose of the Pfizer-BioNTech vaccine, people are less likely to develop antibody levels against the B.1.617.2 variant as high as those seen against the previously dominant B.1.1.7 (Alpha) variant, first found in Kent. The team, led by researchers from the Francis Crick Institute in the UK, noted that 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, they said.

The study analysed antibodies in the blood of 250 healthy people who received either one or two doses of the Pfizer-BioNTech COVID vaccine, up to three months after their first dose.

After a single dose of Pfizer-BioNTech, 79 per cent of people had a quantifiable neutralising antibody response against the original strain, but this fell to 50 per cent for B.1.1.7, 32 per ce nt for B.1.617.2 and 25 per cent for B.1.351 or Beta variant first discovered in South Africa. While antibody levels decreased with age against all variants, no correlation was observed for sex or body mass index (BMI).