Shorter Dose Gap More Effective Against Delta Variant, Says Lancet Study

The recommendation is at odds with India's recent decision to increase the gap between two Covishield doses to 12 to 16 weeks from six-eight weeks.

The Pfizer vaccine is far less effective against the Delta variant of Covid, which is dominant in India, compared to the original strain of the coronavirus, says The Lancet journal in a new study. The antibody response to variants is even lower in people who have received just one dose and a longer gap between doses may significantly reduce antibodies against the Delta variant, the study says. After a single dose of Pfizer, 79 per cent of people had quantifiable neutralising antibody response against the original strain, but this fell to 50 per cent for B.1.1.7 or Alpha variant, 32 per cent for Delta and 25 per cent for the B.1.351 or Beta variant first discovered in South Africa. The researchers note it is most important to ensure that vaccine protection remains high enough to keep as many people out of hospital as possible. "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," says Emma Wall, UCLH Infectious Diseases consultant and Senior Clinical Research Fellow for the Legacy study.