While the ACT gives itself a well-deserved collective pat on the back for achieving the milestone of 95 per cent double-dose vaccination for its 12-plus population, medical researchers are warning that without timely booster shots, the population could find itself back to below herd immunity levels and at risk of a third wave.
Research published in The New England Journal of Medicine found Pfizer vaccines offered at least 90 per cent protection against severe COVID-19 cases for at least six months; however, six months after the second Pfizer dose, the vaccine provided less than 20 per cent protection against milder infections of the virus.
The co-author of the research, epidemiologist and Aspen Medical group medical director Andrew Jeremijenko, said that with immunity waning after six months, the effective 95 per cent vaccination rate would start to drop.
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Dr Jeremijenko said the vaccines will remain effective against severe infection, resulting in hospitalisation and death, for longer than six months, but noted with waning effectiveness, the chance of acquiring the virus and passing it on will increase.
A study undertaken by University of Oxford scientists published in August found that the effectiveness of the Pfizer vaccine declines slightly faster than that of AstraZeneca.
Without booster shots, Dr Jeremijenko suggested Australia may end up with a similar experience to Israel which had a spike in cases six months after its vaccination program started, creating a third wave.
Like Israel, Australia has experienced very low infection levels from the SARS-CoV-2 virus compared with other countries. Dr Jeremijenko says this means boosters are crucial to maintaining herd immunity.
“Places where infection rates were low will be especially reliant on booster shots to prevent further waves,” Dr Jeremijenko said.
This is different for countries like Qatar where SARS-CoV-2 infection rates were higher.
A Qatar study co-authored by Dr Jeremijenko showed that prior infection was associated with a lower risk for breakthrough infection among persons receiving the mRNA vaccines like Pfizer and Moderna, meaning natural immunity from infection together with vaccination together lasts longer than vaccinated immunity.
Several recent studies showed Moderna’s shot elicits a stronger and longer-lasting immune response than the Pfizer jab. Some scientists believe this is because Moderna’s mRNA dose is more than triple that of Pfizer.
While studies are continuing, Dr Jeremijenko says it was clear that while vaccine efficacy waned over time, every country would probably need to follow Israel’s lead in administering boosters to its entire population with older adults and those in a clinical risk group prioritised for booster doses.
The ACT Government has opened bookings for its booster shot program. People who received the vaccine at least six months ago are now eligible for their top-up.