An interval of several months between the first and the second dose of AstraZeneca / Oxford vaccine against Covid-19 improves the immunity provided, indicates a study published on Monday by the University of Oxford, which sees it as a "
reassuring
"
element
for countries with supply problems.
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The researchers showed that far from affecting the effectiveness of the vaccine, an interval of up to 45 weeks between the two doses improved the immune response to the virus.
“
This should be reassuring news for countries with less vaccine supplies, who may be concerned about delays in getting second doses to their populations.
There is an excellent response to a second dose, even after a delay of 10 months from the first,
”commented Professor Andrew Pollard, director of the Oxford Vaccine Group which developed the vaccine with the Anglo-Swedish pharmaceutical group.
Third dose well tolerated
In February, a study from the University of Oxford published in The Lancet had already indicated that the effectiveness of the vaccine was greater with an interval of 3 months between doses (81%), than after an interval of 6 weeks. (55%). In their study published Monday, the researchers also showed that a third dose injected more than six months after the second causes a "
significant increase
" in antibodies and causes a "
sharp rise
" in the immune response against Covid-19, including included against variants.
“
It is not known whether booster injections will be necessary due to decreased immunity or to increase immunity against the variants of concern,
” said Teresa Lambe, lead author of these studies.
But the professor notes that research shows that a third dose of the vaccine “
is well tolerated and considerably increases the antibody response.
This is very encouraging news, if we find that a third dose is necessary
”.
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The researchers note that the vaccine had "
fewer cases of side effects after the second and third doses than after the first
". The AstraZeneca vaccine, which uses so-called “
viral vector
” (adenovirus) technology, has raised concerns after a link was established between serum and very rare but often fatal blood clots. Many countries have suddenly restricted its use to the elderly and some have stopped using it.