A study by the Oxford University has revealed that a delayed second and third doses of the AstraZeneca vaccine is likely to boost immunity against Covid-19.

An interval of up to 45 weeks between the first and second dose of the AstraZeneca vaccine led to an enhanced immune response, rather than compromising immunity, the study said.

Giving a third dose of the jab more than six months after the second dose also leads to a "substantial increase" in antibodies and induces a "strong boost" to subjects' immune response, said the pre-print study, meaning that it has yet to be peer-reviewed.

There is an excellent response to a second dose, even after a 10-month delay from the first, said lead investigator of the Oxford trial Andrew Pollard.

"It is not known if booster jabs will be needed due to waning immunity or to augment immunity against variants of concern," said the study's lead senior author, Teresa Lambe. She explained the research showed the AstraZeneca jab "is well tolerated and significantly boosts the antibody response."

The results, published by the University of Oxford on the pre-print server of The Lancet, demonstrated that antibody levels remain elevated from baseline for at least one year following a single dose.

An extended interval between the first and second dose of Vaxzevria of up to 45 weeks, resulted in up to an 18 fold increase in antibody response, measured 28 days after the second dose. With a 45-week dosing interval between the first and second dose, antibody titres were four times higher than with a 12-week interval, demonstrating that a longer dosing interval is not detrimental but can derive stronger immunity.

In addition, the third dose of Vaxzevria given at least 6 months after a second dose, boosted antibody levels sixfold and maintained T cell response. A third dose also resulted in higher neutralising activity against the Alpha (B.1.1.7, 'Kent'), Beta (B.1.351, 'South African') and Delta (B.1.617.2, 'Indian') variants.

Both the late second dose and the third dose of Vaxzevria were less reactogenic than the first dose

The researchers said the results for a delayed AstraZeneca third dose were positive, particularly as nations with advanced vaccination programmes consider whether third booster shots will be required to prolong immunity.

Inputs Source: AstraZeneca.com

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