An interval of several months between the first and second doses of the Covid-19 vaccine developed by AstraZeneca / Oxford improves immunity, according to a study published Monday by the University of Oxford.

The researchers showed that, far from reducing the effectiveness of the vaccine, an interval of up to 45 weeks between the two doses improves the immune response to the virus.

"This should be reassuring news for countries with fewer vaccine supplies, which may be concerned about delays in getting second doses for their populations," said Professor Andrew Pollard, director of the Oxford Vaccine Group, which developed the vaccine. with the Anglo-Swedish pharmaceutical group AstraZeneca.

"There is an excellent response to the second dose even 10 months after receiving the first," he stressed.

Another Oxford University study published in February by the prestigious scientific journal in The Lancet already indicated that the efficacy of the vaccine was greater with a three-month interval between doses (81%) than with a six-week interval (55 %).

As a result of this new study, the researchers also discovered that a third dose injected more than six months after the second leads to a “significant increase” in antibodies and causes a “strong increase” in the immune response against Covid- 19, including against known variants of the coronavirus.

"We do not know whether booster injections will be needed due to decreased immunity or to increase immunity against variants," said Teresa Lambe, lead author of the studies. But she noted that the research shows that a third dose of the vaccine "is well tolerated and significantly increases the response to the level of antibodies."

"It is very encouraging news if a third dose is found to be necessary," she added.

The researchers also claim that the vaccine caused "fewer side effects after the second and third doses than after the first."