International

Late second dose and third doses of AZ vaccine lead to heightened immune response: Oxford Uni

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 University of Oxford said last Monday (28).

According to the University, 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. 

Following the University’s examination of 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.

It was also highlighted that 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.’

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.

‘It is not known if booster jabs will be needed due to waning immunity or to augment immunity against variants of concern,’ says Associate Professor Teresa Lambe OBE, lead senior author for these studies. ‘Here we show that a third dose of ChAdOx1 nCoV-19 is well tolerated and significantly boosts the antibody response. This is very encouraging news, if we find that a third dose is needed.’

Side effects of the vaccine itself were also found to be well-tolerated, with lower incidents of side effects after second and third doses than after first doses.

The University says that further research is required to follow up with study participants who received third doses beyond the period that was part of the initial study.