People fully vaccinated with the Pfizer-BioNTech vaccine are likely to have more than five times lower levels of neutralising antibodies against the Delta variant first identified in India compared to the original strain, according to research published in The Lancet journal.
Lancet 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.