The safety of Comirnaty (Pfizer) and Vaxzevria (AstraZeneca) vaccines has been confirmed by a study of more than three million Australians who’ve receive these injections.
Published in the Medical Journal of Australia, the study by AusVaxSafety analysed the short-term safety of COVID vaccines implemented in the first stages of Australia’s rollout.
Although reporting of adverse events – that means any negative reaction to a vaccine, no matter how minor – was comparatively higher than for the seasonal flu vaccine, the results support existing studies validating the short-term safety profile of Australia’s recommended COVID jabs.
“I don’t think that’s surprising in any way,” says lead author Dr Lucy Deng, clinical lead at AusVaxSafety. “Right from the beginning, we were told mRNA vaccines [such as Comirnaty] were a little bit more reactogenic, so we expected more common adverse events such as local reactions, fevers, joint pain.
“Actually, most of these adverse events subside pretty quickly; in our study we showed that most of the adverse events dropped significantly by about day eight.
“You’re really only having those side effects for a very short period of time and not that many people needed time off work, or activities of daily living.”
Common symptoms consistent with previous reports
The most reported adverse symptoms included injection site pain, fatigue, headache, and myalgia (muscular aches and pains).
Of those respondents to receive the Comirnaty vaccine, 35.9% reported one or more adverse events after the first dose, and 54.7% after the second. For the Vaxzevria vaccine, 52.8% reported an adverse event after their first dose, and 22% after the second.
The same surveillance system reports adverse events in just under 20% of seasonal flu vaccine recipients, though from a much smaller sample.
Just 0.9% of respondents sought medical advice in the three days after COVID vaccination. That metric is used by AusVaxSafety as a proxy for serious adverse events and is consistent with the medical attendance rate of under 0.5% for the seasonal flu vaccine.
And by including participants with comorbidities – a demographic often excluded from clinical studies – the study gives a more realistic snapshot of adverse events within the population.
This, says Deng, should give greater confidence to those suffering from other health issues seeking vaccination. “They generally have very healthy people in clinical trials, whereas our surveillance system covers everyone who was eligible for vaccination,” she says.
“The paper delves into people who’ve had a chronic medical condition. That’s really important if, for example, you’re a person who’s living with cancer, who’s had a bone marrow transplant, you probably want to know what sort of adverse events to expect after your COVID vaccine so you can manage them appropriately.”
Ongoing surveillance provides real time updates on vaccine safety
AusVaxSafety was established by the Sydney-based National Centre for Immunisation Research and Surveillance in response to adverse events reported among children who received a seasonal flu vaccine in 2014.
Working with state and territory health departments, surveys were sent via text message or email to those who attended government-run vaccination hubs, while scannable QR codes were provided to those who attended smaller and remote clinics.
“We were able to capture a very representative sample of Australia right from the beginning,” says Deng. “To allow us to survey over three million people in less than six months is unheard of.”
While surveillance data from the first six months of the Australian vaccine rollout forms the basis of the AusVaxSafety report, data updates are regularly published on the organisation’s website.
Winter booster expansion begins today
Over 95% of Australians have received two initial doses of either the Comirnaty, Spikevax (Moderna), Vaxzevria or Nuvaxovid (Novavax) vaccines.
That number falls away for the booster dose, with just over 70% of eligible people receiving the third jab.
From Monday 11 July, Australians aged over 50 are recommended to receive a fourth or ‘winter’ dose of approved vaccine. People aged 30–49 are also eligible.
The expansion of the fourth dose to those aged over 30 is aimed to expand protection against COVID-19 with an expected increase in cases due to new Omicron subvariants circulating in the population.
Next-generation vaccines based on the Omicron strain are still in development.
Matthew Agius is a science writer for Cosmos Magazine.
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