* No evidence yet that booster shots are needed
* Antibodies also higher after greatly delayed second dose
* Study helps soothe worries over repeat use of viral vector
By Alistair Smout
LONDON, June 28 (Reuters) - A third shot of the
Oxford-AstraZeneca COVID-19 vaccine produces a strong
immune response, researchers said on Monday, adding there was
not yet evidence that such shots were needed, especially given
shortages in some countries.
The Oxford University study found that a third dose of the
vaccine increases antibody and T-cell immune responses, while
the second dose can be delayed up to 45 weeks and also lead to
an enhanced immune response.
The British government has said it is looking at plans for
an autumn vaccine booster campaign, with three-fifths of adults
already having received both doses of a COVID vaccine.
Andrew Pollard, director of the Oxford Vaccine Group, said
that evidence that the vaccine protects against current variants
for a sustained period of time meant that such a booster may not
"We do have to be in a position where we could boost if it
turned out that was necessary ... (but) we don't have any
evidence that that is required," he told reporters.
"At this point with a high level of protection in the UK
population and no evidence of that being lost, to give third
doses now in the UK whilst other countries have zero doses is
Studies had previously shown that the shot, invented at
Oxford University and licensed to AstraZeneca has higher
efficacy when the second dose is delayed to 12 weeks instead of
Monday's research was released in a preprint, and looked at
30 participants who received a late second dose and 90 who
received a third dose, all of whom were under 55.
It helps assuage concerns that viral vector COVID vaccines,
such as those made by AstraZeneca and Johnson & Johnson,
may lose their potency if annual inoculations are needed due to
the risk that the body produces an immune response against the
vectors that deliver the vaccine's genetic information.
"There had been some concerns that we would not be able to
use this vaccine in a booster vaccination regime, and that's
certainly not what the data is suggesting," study author Teresa
Lambe of Oxford's Jenner Institute told Reuters.
(Reporting by Alistair Smout; additional reporting by Natalie
Editing by Gareth Jones)