Australians may need to receive two or even three Covid jabs each year to maintain defense against the virus, if early results on the effectiveness of booster shots prove to be a useful guide.
Weekly data published just before Christmas by the UK Health Safety Agency show that the efficacy of both Pfizer and Moderna boosters against symptomatic diseases is lower for Omicron than the Delta variant in all post-injection periods.
The analysis included 147,597 Delta and 68,489 Omicron cases in the United Kingdom. The agency stressed that “the results should be interpreted with caution due to the low numbers and the possible imbalances related to the populations with the highest exposure to Omicron (including travelers and their close contacts), which can not be fully accounted for”.
The UK data showed that both Pfizer and Moderna boosters had 90% efficacy against symptomatic diseases from the Delta variant for up to at least nine weeks.
In contrast, the efficacy against the Omicron strain was about 30% lower and appeared to decrease 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 center is considering recommending staff to have a new booster.
Medical experts in Australia said results beyond the 12-week dataset would be needed to get a long-term picture.
Jaya Dantas, professor of international health at Curtin University, said it was still early days for understanding the effectiveness of vaccinations, but “it seems that regular boosters may be needed”.
“You may need boosters, such as two a year or three a year,” Dantas said, with older people more likely to be queuing for a triple annual dose.
The virus has so far spawned 11 variants, with Delta and now Omicron being the most contagious. Ten of these tribes had appeared in developing parts of the world.
“We have vaccine inequality,” Dantas said, with the gap likely to widen as booster demand grows in richer nations. “So many parts of Africa have not even received a single dose, or they have had very low levels of a single dose.”
Michael Lydeamore, an infectious disease model at Monash University, said it was reassuring from the UK study that “no matter what your first two first-dose vaccines were – so either AstraZeneca, Pfizer or Moderna – you get pretty much the same protection” from Pfizer or Modern booster.
“It’s really important because we know AstraZeneca protection is a bit lower to begin 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 January 4 and then to three months on January 31, making millions of people eligible in the coming weeks.