Australians may have to receive two or even three Covid jabs each year to maintain defences against the virus if early results on the efficacy of booster shots turn out to be a useful guide.
Weekly data published just before Christmas by the UK’s Health Security Agency shows the effectiveness of both the Pfizer and Moderna boosters against symptomatic diseases is lower for the Omicron than the Delta variant across all periods after the injection.
The analysis included 147,597 Delta and 68,489 Omicron cases in the UK. The agency stressed the “results should be interpreted with caution due to the low counts and the possible biases related to the populations with highest exposure to Omicron (including travellers and their close contacts) which cannot fully be accounted for”.
The UK data showed both Pfizer and Moderna boosters had 90% effectiveness against symptomatic diseases from the Delta variant up to at least nine weeks.
By contrast, efficacy against the Omicron strain was about 30% lower, and appeared to drop away further after nine weeks.
Israel has already begun administering a second booster dose to follow the original three-dose treatment, and at least one US medical centre is considering recommending staff have a second booster.
Medical experts in Australia said results beyond the 12-week dataset would be needed to get a longer term picture.
Jaya Dantas, a professor of international health at Curtin University, said it was still early days for the understanding of the efficacy of the vaccinations but “it appears that there might be a need for regular boosters”.
“You might need boosters, say maybe two a year or three a year,” Dantas said, with elderly people more likely to be in line for a triple annual dose.
The virus has so far spawned 11 variants, with Delta and now Omicron the most contagious. Ten of those strains had emerged in developing parts of the world.
“We have vaccine inequity,” Dantas said, with the gap likely to widen as booster demand grows in wealthier nations. “So many parts of Africa have not even had one single dose, or they’ve had very low levels of a single dose.”
Michael Lydeamore, an infectious disease modeller at Monash University, said it was reassuring from the UK study that “no matter what your initial first two vaccine doses were – so either AstraZeneca, Pfizer or Moderna – you get basically the same protection” from the Pfizer or Moderna booster.
“That’s really important, because we know the AstraZeneca protection is a bit lower to start with than Pfizer,” Lydeamore said “But both go up to about the same level after a booster, so that’s really good.”
As of Thursday just over 2 million Australians had received a single booster – 8.3% of the total population. Last week the federal government agreed to cut the minimum interval between second dose and booster from five to four months on 4 January, and then to three months on 31 January, making millions more people eligible in coming weeks.
