Oxford study finds highest antibody boost for ten-month gap between AstraZeneca doses

A study by the University of Oxford published on Monday has revealed that the human body's immune response to the AstraZeneca Covid-19 vaccine is likely to be more effective if the gap between two doses is increased to about 10 months. Additionally, a third shot can push up the antibody levels, even more, said the study conducted on the vaccine now known as Vaxzevria.

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.

The lead investigator of the Oxford trial, Andrew Pollard noted that the findings from the study was a 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."

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.

"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."

Lambe added results were encouraging "if we find that a third dose is needed".

The development of the jab, which is being administered in 160 countries, has been hailed as a milestone in efforts against the pandemic because of its relatively low cost and ease of transportation.

However, confidence in the jab, as with the vaccine developed by the US firm Johnson & Johnson, has been hampered by concerns over links to very rare but serious blood clots in a handful of cases.

A number of nations have suspended the use of the vaccine as a result or restricted its use by younger groups who are less at risk from Covid.

The Oxford study indicated that side effects from the vaccine in general were "well tolerated" with "lower incidents of side effects after second and third doses than after first doses".