RIO DE JANEIRO, BRAZIL – A third dose of AstraZeneca’s Covid-19 vaccine from Oxford University produces a strong immune response, researchers said Monday, adding that there is no evidence yet that such a booster dose is required, particularly given vaccine shortages in some countries.
The Oxford University study showed that a third dose of the vaccine boosts antibody and T-cell immune responses, while the second dose administration may be delayed until up to 45 weeks after the first and still lead to an enhanced immune response.
The UK government says it is considering plans for a booster dose campaign in the Northern Hemisphere autumn, with three-fifths of adults having been administered both Covid-19 vaccine doses.
Andrew Pollard, director of the Oxford Vaccine Group, said that evidence that the vaccine protects against existing variants for a sustained period means that a booster dose may not be required.
“We need to be in a position where we can administer the booster dose should it prove necessary … (but) we have no indication that it will be,” he told reporters.
“At the moment, with a high protection rate in the UK population and no evidence that this has been lost, administering third doses in the UK while other countries have zero doses is not acceptable.”
Earlier studies have shown that the vaccine, developed by Oxford University and licensed by AstraZeneca, has a higher efficacy when the interval between doses is extended to 12 weeks rather than 4 weeks.
The research announced on Monday was released in a pre-print, with no peer review by other scientists, and analyzed 30 participants who were administered a delayed second dose and 90 who were administered a third dose. All participants were under the age of 55.
The study helps ease concerns that viral vector-based Covid-19 vaccines, such as AstraZeneca and Johnson & Johnson’s may lose their potency if annual booster doses are required, given the risk that the body will produce an immune response against the vectors carrying the vaccine’s genetic information.
“There have been some concerns that we couldn’t use this vaccine on a booster dose regimen, and that’s certainly not what the data are suggesting,” study author Tereza Lambe of Oxford’s Jenner Institute said.