Elderly to need Covid-19 vaccine booster as effect wears off

Booster shots for residents in aged care centres may need to begin being administered early next year as evidence grows that Covid-19 immunity begins to decline after six months.

Australia has ordered an extra 85 million doses of the Pfizer vaccine to allow for booster shots. Picture: AFP

Booster shots for residents in aged care centres may need to begin being administered early next year as evidence grows that immunity conferred by Covid-19 vaccines begins to decline after six months.

Australia has ordered an extra 85 million doses of the Pfizer vaccine to allow for booster shots, and will also likely use the 50 million doses of Novavax that have been bought as boosters. In addition, Australia has purchased 15 million doses of the specific booster vaccine that Moderna is developing.

Israel has already begun administering booster shots, and Britain plans to begin delivering boosters to the elderly from next month. Germany is also set to start administering boosters to the most vulnerable from next month.

However, the World Health Organisation has called on ­nations to halt giving booster vaccines until at least the end of September so that vaccine doses can go to countries that have not yet had the opportunity to inoculate large proportions of their populations.

“I understand the concern of all governments to protect their people from the Delta variant. But we cannot accept countries that have already used most of the global supply of vaccines using more of it,” WHO director-general Ted­ros Adhanom Ghebreyesus said.

Preliminary studies in Israel have indicated that while antibody levels in people given two shots of the Pfizer vaccine are still high six months after vaccination, they gradually begin to decline.

Pfizer chief executive Albert Bourla has said people would likely need a booster dose within 12 months of being fully vaccinated.

But Helen Marshall, an associate professor in vaccinology at the Adelaide Medical School, said there was not yet a large tranche of scientific data on how long antibodies remained in the blood.

“It’s still a bit undetermined when boosters will be required,” Professor Marshall said.

“The data on immunity is looking good certainly out to six months and likely out to a year at this stage. That information is still accumulating (but) I think we can be reasonably confident about the length of protection six to 12 months after vaccination.”

Britain is running clinical trials to see whether a “mix-and-match” approach of boosting with a different type of vaccine to one the originally given is more effective as a strategy than boosting with another shot of the same type.

“The booster is like giving you a boost in your antibody level, that’s what it’s designed to do,” said University of Sydney professor Nicholas Wood, who leads the NSW Immunisation Specialist Service.

“And what they’ll be doing in these booster studies is comparing how fast the antibody rises and how high it rises in those people who have been primed with Pfizer and those people who have been primed with AstraZeneca.

“The idea is because you’ve got these memory cells set up as a ­result of the initial vaccination, you make antibodies faster, and you make more of them.”

The National Institutes of Health in the US is also sponsoring a study into the potential benefit of using a different type of vaccine as a booster. If those studies find this is the case, it is likely people who had Pfizer as their first vaccine may be given Novavax as the booster, while people who had ­AstraZeneca may receive Pfizer as a booster.