Research on the ChAdOx1 nCoV-19, also known as the Oxford-AstraZeneca vaccine, indicates that a long interval between first and second doses does not compromise the immune response after a late second dose, and a third dose of the vaccine continues to boost antibodies against SARS-CoV-2. The results were released in a preprint today.
COVID-19 vaccine supply shortages are causing concerns in some countries about compromised immunity as the interval between first and second dose extends due to limited vaccine availability. When examining the effects of a delay of up to 45 weeks between first and second doses in study participants, results demonstrated that antibody levels were increased after a delayed second dose. Additionally, a longer delay between first and second doses may be beneficial, resulting in an increased antibody titre and enhanced immune response after the second dose.
Professor Sir Andrew Pollard, Professor of Paediatric Infection and Immunity and Lead Investigator of the Oxford University trial of the vaccine, says, ‘This should come as reassuring news to countries with lower supplies of the vaccine, who may be concerned about delays in providing second doses to their populations. There is an excellent response to a second dose, even after a 10 month delay from the first.’
Conversely, some countries are considering administering a third ‘booster’ dose in the future. Studying the impact of a third vaccine dose, the researchers found that antibody titres increased significantly with a third dose. T-cell response and the immune response against variants were also boosted.
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