Health experts may soon recommend a third jab for the COVID-19 AstraZeneca vaccine after a study by Oxford University established that a third dose, at least six months after the second, raises immunity back to peak levels.
The study also showed that a long interval between the first and second doses does not compromise the immune response.
When the AstraZeneca vaccine was first being administered in Kenya, the interval period between the first and second dose was given as 8 weeks.
But with the delay in the arrival of subsequent consignments of doses as expected, the interval period was further extended to 12 and up to 16 weeks.
When examining the effects of a delay of up to 45 weeks between first and second doses in study participants, the research 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 or concentration and enhanced immune response after the second dose.
Prof. Sir Andrew Pollard, Professor of Paediatric Infection and Immunity and lead investigator of the Oxford University trial of the vaccine, said: “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 concentrations increased significantly with a third dose; T-cell response and the immune response against variants were also boosted.
According to Prof. Teresa Lambe, the lead senior author for these studies, “It is not known if booster jabs will be needed due to waning immunity or to augment immunity against variants of concern. Here we show that a third dose of ChAdOx1 nCoV-19 vaccine is well tolerated and significantly boosts the antibody response. This is very encouraging news, if we find that a third dose is needed.”
However, Dr. Willis Akhwale, the chair of the vaccine, says: “The findings are good but it will be more important if we seek answers as at what point after the first dose do the antibodies wane off completely? Single shot vaccinations will be easier to deploy in developing countries since they will require less operational costs.”
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.
Further research is required to follow up with study participants who received third doses beyond the period that was part of the initial study.
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