Levels of antibodies in the blood of vaccinated people that are able to recognise and fight the new SARS-CoV-2 Delta variant first discovered in India (B.1.617.2) are on average lower than those against previously circulating variants in the UK, according to new laboratory data from the Francis Crick Institute and the National Institute for Health Research (NIHR) UCLH Biomedical Research Centre, published, published as a Research letter in The Lancet.

The results also show that levels of these antibodies are lower with increasing age and that levels decline over time, providing additional evidence in support of plans to deliver a vaccination boost to vulnerable people in the Autumn.

And, the researchers support current plans 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 (Delta) variant as high as those seen against the previously dominant B.1.1.7 (Alpha) variant, first found in Kent.

Although laboratory results such as these are needed to provide a guide as to how the virus might be evolving to escape the first generation of vaccines, 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.

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), as evidence of the level of protection people might receive against the new variants after one dose and both doses of the Pfizer COVID-19 vaccine. ...