The AstraZeneca Covid-19 vaccine produces an improved immune response with a longer dose gap of up to 45 weeks, and a third shot is able to boost antibody levels even further, according to a study in the UK.
The yet-to-be peer-reviewed study shows that antibody levels remain elevated for at least one year following a single dose of the Oxford-AstraZeneca vaccine, known as Covishield in India where the gap between its two doses has been set at 12-16 weeks.
The authors of the study noted that an extended interval of up to 45 weeks, or about 11 months, between the first and second dose of AstraZeneca vaccine resulted in up to an 18-fold increase in antibody response measured 28 days after the second dose.
The research, posted on the pre-print server of The Lancet on Monday, included volunteers aged 18 to 55 years who had already received either a single dose or two doses of AstraZeneca vaccine.
The researchers from University of Oxford in UK assessed immune response after a single dose, immunity after an extended interval between the first and second dose, and the response to a third dose as a late booster.
With a 45-week dosing interval between the first and second dose, antibody levels were four times higher than with a 12-week interval.
The researchers noted that some countries are considering administering a third 'booster' dose in the future.
Studying the impact of a booster, they found that the dose given at least six months after a second dose boosted antibody levels six-fold and maintained T cell response.
A third dose also resulted in higher neutralising activity against the Alpha, Beta, and Delta variants, according to the findings of the study.