The immune response to the AstraZeneca COVID-19 vaccine, manufactured as Covishield in India, is likely to be more effective if the gap between the two doses is increased to about 10 months, according to a study by the Oxford University researchers.
The study also found that a third dose given more than six months after the second dose leads to a substantial increase in antibodies and induces a strong boost to immune response against the virus, including variants.
The results of the study were released in a preprint on Monday, 28 June. The study is yet to peer-reviewed.
Why Is the Study Significant?
"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," the study said.
The study is significant as amid the vaccine supply crunch many countries, including India, have chosen to delay the interval between the doses.
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.Andrew Pollard, Lead Investigator of the Oxford University trial
Meanwhile, some countries are also mulling a third booster dose in the future, due to waning immunity or for protection against emerging variants.
The researchers found that antibody titres increased significantly with a third dose. T-cell response and the immune response against variants were also boosted.
"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," says Associate Professor Teresa Lambe OBE, lead senior author for these studies.
What about side effects?
They were also found to be well-tolerated, with lower incidents of side effects after second and third doses than after first doses, study showed.
What Are the Findings of the Study?
Volunteers in the latest study were drawn from Oxford’s original early and late-stage trials for the vaccine last year, according to Bloomberg.
All volunteers were between the ages of 18 and 55.
The study found that antibodies induced after a single dose survived to some extent after one year. The levels peaked at 28 days and halved by 180 days. A second dose increased antibody responses between four- and 18-fold by one month after administration of the dose.
Further, the researchers found that the antibody titers were at 923 in those who were given the second dose in the 8-12 week interval, 1,860 in 15-25 week interval and 3,738 in those who were administered the second dose in the 44-45 week intervals.
Higher levels of neutralising antibodies against the alpha, beta and delta variants of COVID-19 were also shown after a third dose compared with a second. This supports the idea that viral-vector vaccines can be used as boosters.
(With inputs from Bloomberg.)
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