A delayed second or third dose of the Oxford-AstraZeneca vaccine can produce a strong immune response against COVID-19, researchers said, adding that there was not yet evidence that these shots were needed, especially given shortages in some countries.
A recent study by the Oxford University found that a third shot of the vaccine can boost the 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 stated it is planning for an autumn vaccine booster campaign, with three-fifths of adults already having received both doses of a COVID-19 vaccine.
The evidence that the vaccine protects against current variants for a sustained period of time meant that such a booster may not be needed, Mr. Andrew Pollard, director of the Oxford Vaccine Group, said.
“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 is required. 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 not acceptable,” Mr. Pollard explained.
Studies had previously shown that the vaccine, invented at Oxford University and licensed to AstraZeneca has higher efficacy when the second dose is delayed to 12 weeks instead of four weeks.
The research was released in a preprint and looked at 30 participants who received a late second dose and 90 who received the third dose, all of whom aged under 55.
It helps assuage concerns that viral vector COVID-19 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 Ms. Teresa Lambe of Oxford’s Jenner Institute stated.