Health experts are weighing up whether a second booster rollout will soon be needed as Covid-19 cases again surge across Australia and winter approaches. A number of nations, including the UK, are rapidly expanding eligibility for a fourth dose, but some experts have questioned its effectiveness.
How likely is it a fourth dose will be required?
The government has yet to commit to a second booster rollout. However, it is expected older Australians will be the first to be eligible when it does begin.
Earlier in March the federal health minister, Greg Hunt, said advice from Australia’s vaccine advisory group was due by the end of the month on whether a fourth dose would be recommended for people aged 65 and over.
Hunt said it was more likely than not a fourth dose would be needed for some groups of the population ahead of winter, when a spike in both Covid and flu infections is forecast.
“I can’t pre-empt the decision but … they are potentially going to recommend a second booster, which would be potentially the start of an annual program for people 65 and above,” Hunt said.
“We’re expecting that advice from Atagi within the next three weeks, if not earlier.”
Who is already eligible for a fourth dose?
A limited number of people are eligible already. A fourth vaccination dose is recommended for severely immunocompromised people aged over 16, who produce a lower immune response than the equivalent number of doses in healthy people.
Earlier this year, adults with weakened immune systems, including cancer patients, became eligible to receive a fourth vaccination after Atagi guidelines changed due to the Omicron outbreak.
Last month, the booster program was further expanded to severely immunocompromised adolescents aged 16 and 17.
A fourth dose can be administered three months after the completion of an immunocompromised person’s primary course – currently three doses.
Cancer Australia CEO, professor Dorothy Keefe, said immunocompromised people could have a prolonged Covid infection which increased the risk of viral variants developing.
“As people who are severely immunocompromised may have a suboptimal response or non-response to the standard two-dose primary vaccine schedule, Atagi recommends … a fourth dose … to increase their protection,” she said.
What countries are administering fourth doses?
Until recently, a number of countries including the US, Chile, Denmark, Germany, Sweden and the UK were similarly limiting second boosters to the immunocompromised.
But this week, England expands its eligibility to about five million people including care home residents, people over 75 and immunocompromised people aged over 12. It follows a resurgence of Covid cases across the UK, with infections in the over-70s at a record high.
Similarly in Asia, South Korea is recommending a fourth dose for nursing home and care residents and workers as well as the immunocompromised in light of rising infections among elderly people.
Israel was the first country to administer a fourth dose more widely. It began to roll out third doses in July, and since January, anyone who is a health worker, immunocompromised, or over 60 has been eligible for a fourth vaccine. Israeli health experts have since suggested a fourth dose for all adults.
Last week, Pfizer and BioNTech requested emergency authorisation from the US Food and Drug Administration for a fourth dose among the over 65s, citing Israeli datasets which showed an additional mRNA booster lowered infections and severe illness.
How effective would a fourth dose be in Australia?
There’s mixed evidence on the effectiveness of a second booster, however the risk calculation is evolving as new Covid variants emerge.
Deakin University chair of epidemiology, Prof Catherine Bennett, said it was still too early to tell what cover the third dose provided and whether vaccinating with a fourth dose would change health outcomes.
But she said Australia had the benefit of being one season behind and being able to monitor what was occurring in the rest of the world.
“What we don’t yet know is if Covid will ever become a winter bug,” she said. “Omicron reached us in the peak of summer, if we reach a period where we don’t see new variants and none end up being infectious enough to replace what we have, it might slope back into something more seasonal.”
The Omicron sub-variant BA.2 is on the rise in Australia, and is expected to become the dominant strain of Covid-19 in the coming months. It is highly likely BA.2, which shares similar mutations to Omicron, will be similarly resistant to a third dose.
Nevertheless, Australian regulators require strong data before approving additional doses. After its latest meeting on 11 March, Atagi said it was “continuing to monitor and discuss” emerging evidence on subsequent booster doses “particularly coming into the winter months”.
An Israeli trial released in February suggested receiving a fourth vaccine raised antibody levels, but provided little extra protection against Covid-19 in addition to a third dose.
New research published in the New England Journal of Medicine this month, though, shows immunity from a third jab wanes quickly – dropping to about 45% with the Omicron strain ten weeks after a third Pfizer dose despite its initial protection from severe illness.
Bennett said no matter what Atagi decided, immunity was likely to be different for younger versus older and immunocompromised adults. “We don’t treat everyone as one, if it’s good enough from the booster there’s no point in giving another dose … and there’s a risk it might desensitise you to the virus,” she said.
Why are third doses still lagging?
The Royal Australian College of General Practitioners (RACGP) president, Dr Karen Price, said it was a “matter for the government” as to whether a fourth dose should be rolled out to the general population. But there were “several reasons” why booster rates remained sluggish.
As of 13 March, only 65.6% of eligible people had received a third vaccine dose, while in Aboriginal and Torres Strait Islander communities, just 49.4% had the jab.
“Some patients are uncertain about when to get their booster dose after contracting the virus and others are potentially complacent because of widespread media reports about the Omicron variant being less severe,” Price said.
“It’s not just about protecting yourself, it’s also about protecting the broader community including people more vulnerable to severe effects from the virus.”
What about the flu jab?
The seasonal flu all but disappeared in 2020 and 2021 due to public health measures, however Atagi expects a resurgence of the virus outside the usual influenza season as international borders reopen and with Covid restrictions eased.
There wasn’t a single influenza death in 2021, while case numbers were at 3% of those recorded in 2020 – which was already eight times lower than the five-year average of 163,015 cases.
Atagi said lower vaccine coverage in 2021 and virus circulation meant many children under five hadn’t been exposed to the virus or developed immunity, thereby increasing the risk of complications.
Atagi has recommended those planning an international trip receive the influenza vaccine before they fly, and get vaccinated as soon as this year’s jab becomes available.
Bennett said this year the population didn’t have the “natural boost” that came from having relatively high levels of the flu.
“But the flu hasn’t taken off overseas in ways we might have thought it would – there’s some hope it won’t be devastating but we need to be careful,” she said.
As Covid and the flu are different viruses – it’s possible to have both at the same time, ominously dubbed “flurona”.
Bennett said while this was a concern – it wouldn’t necessarily become common.
“The viruses may be competing with each other,” she said. “But we should be very careful about both because … the world’s shifted which makes it more challenging to predict.”
