Dr Gary Grohmann and Prof Robert Booy weigh up the research on boosters

As COVID-19 evolves and government/manufacturers update vaccines to produce 2nd generation more protective products, many people will be asking questions: Should we all line up for a 4th or 5th dose of COVID-19 vaccine? Should we wait for an updated vaccine to the very latest sub-variants? Will we need regular boosters in the future?

Despite high vaccination rates, with over 96% Australians over 16 years having had 2 doses of vaccine and 73% having had 3 doses, the virus has still spread in the community resulting in some 14,000 average daily cases for week ending 9 February 2023, but hospitalisation rates are finally falling.

A recent Australian study showed that a 3rd dose of vaccine resulted in a 65% greater protection against hospitalisation and death than those who only had two vaccine doses. Data from Victoria reported by the ABC shows that 72% of hospitalisations due to COVID-19 are in people who are either unvaccinated or have had 1-2 doses only, and the vast majority of hospitalised cases are in older persons or in those with underlying medical conditions.

A Canadian study showed that a third dose offered a significant increase in protection against hospitalization and death, but a fourth dose gave only a marginal benefit against severe COVID-19.

However, other studies showed that hospital workers who got a fourth dose were far less likely to get COVID-19 than their triple-vaccinated peers.

It is clear that vaccines stop most severe disease, but will not stop infection and spread. It is now well established that immunocompromised persons, people with underlying medical conditions, and those 65 years and over are at high risk of severe outcomes from Omicron.

Until recently, only Australians 65 years and over and vulnerable groups were eligible for a 4th dose.

Now, the Australian Technical Advisory Group on Immunisation (ATAGI) has recommended that people 18 and older who are “at risk” and anyone over 65 receive a booster dose of a COVID-19 vaccine.

The ‘at risk’ group includes:

• all adults aged 65 years or older
• residents of aged care or disability care facilities
• Aboriginal and Torres Strait Islander people aged 50 years or older
• people who are severely immunocompromised
• people aged 16 years or older with a medical condition that increases the risk of severe COVID-19 illness
• people aged 16 years or older with disability, significant or complex health needs, or multiple comorbidities which increase the risk of a poor outcome.

However, the guidance is less clear for ‘At risk’ people between the ages of 5-17 and those with no risk factors between the ages of 18-64; ATAGI says these groups can “consider” a booster.

The benefit of a booster dose for healthy people under 50 years is less certain. Some European countries do not use the mRNA vaccine in healthy persons under 30 years, as it is not clear whether the benefits outweigh the harms due to the possibility of myocarditis, particularly in adolescent and young adult males.

According to WHO, “data to support an additional dose for healthy younger populations are limited; preliminary data suggest that in younger people, the benefit is minimal.”

Nevertheless, boosters make sense for vulnerable groups of any age, as well as travellers, to boost antibody levels.

It comes down to a choice – if you’re healthy and under 65, a booster dose is an option but may have little benefit; but if you’re in a vulnerable group, or 65 years plus, a booster dose would make sense.

Should we wait for an updated vaccine?

Vaccines and boosters currently available include those from Astrazeneca (a Viral vectored vaccine), Novavax (a Protein vaccine) as well as Pfizer and Moderna (mRNA vaccines).

All provide excellent protection against serious outcomes from COVID-19 and there is mounting evidence that protein vaccines have fewer side effects.
The best vaccine to get is the one available now, rather than waiting for updated vaccines; this will maximise protection.

What can we expect going forward?

We will likely need regular boosters in the future, especially for those in vulnerable groups.

The future is bright. New vaccines targeting recent variants are expected, as are combined vaccines for COVID-19 and Influenza, which would probably be updated on an annual basis, targeting recent virus strains. Ideally, we would get a shot of flu/covid around March/April each year and have a covid booster available in September/October for vulnerable groups and those who wish to receive further boosters.

Gary Grohmann is a consultant virologist and an adjunct professor at the University of Sydney. Robert Booy is a consultant paediatrician, infectious disease expert and clinical professor at University of Sydney. Both are Directors of the Immunisation Coalition in Australia.