Restrictions have eased, international borders are open and the flu is back in Australia after a two-year absence.
Suddenly, large flu outbreaks are occurring across the country, catching many unawares.
Influenza vaccinations aim to protect against four influenza viruses that cause disease in humans (two subtypes of influenza A and two of influenza B).
But vaccine-mediated protection varies each year depending on how the vaccine coincides with the flu viruses that cause circulating diseases at any given time. The effectiveness of the vaccine, a real-world measure based on the proportion of vaccinated people who still develop the flu, ranges from 16% to 60%.
However, it is still important to get vaccinated against the flu. If you have been vaccinated and still have the flu, you are less likely to get so sick.
Why it is difficult to predict which subtypes will dominate
Of the four types of influenza virus that exist in nature, two cause major human diseases: influenza A and influenza B.
The 2022 flu vaccine is tetravalent (targeting four different viruses): two influenza A viruses (subtypes H3N2 and H1N1) and two influenza B viruses of different lineages.
Within each subtype of influenza A more genetic variation may arise, with mutations (known as genetic drift) generating many viral variants that are classified into “clades” and subclades.
H3N2 is especially good for generating a lot of diversity in this way. Therefore, predicting exactly which H3N2 virus is targeted to the vaccine is especially difficult.
Read more: Should I Get the 2022 Flu Vaccine? And how effective is it?
A key challenge for flu vaccines is deciding which virus to target should be taken months in advance. The H3N2 virus from the Australian flu vaccine (A / Darwin / 9/2021) was chosen in September 2021 to allow the vaccine to be manufactured and distributed in time for the winter of 2022.
There is no guarantee that a different H3N2 virus that is not so well targeted by the vaccine will not reach the country in the months before winter and start causing disease.
The subtypes contained in the seasonal flu vaccine are selected months in advance. Shutterstock
Another factor that has predicted which H3N2 virus should be targeted at the vaccine by 2022 is the lack of data on which viruses were dominant in previous flu seasons, both in Australia and elsewhere. from the equator.
With the reduction of travel restrictions towards the end of 2021, flu cases began to reappear during the winter 2021-22 of the northern hemisphere. But the lack of flu cases during previous seasons (due to VOCID) meant that the data used to predict which viruses were targeted was inadequate.
The U.S. Centers for Disease Control (CDC) analyzed data from more than 3,000 children and found vaccine efficacy of only 16% protection against mild to moderate H3N2 disease. Protection against the most serious diseases was only 14%.
We do not know which subtypes will circulate in Australia
Data on the effectiveness of the southern hemisphere flu vaccine in winter 2022 are not yet available and it is unclear what protection the current vaccine will have against the subtypes that cause diseases that are currently circulating.
While it now appears that H3N2 viruses are driving some diseases, other flu viruses may be more common later in the season.
The flu vaccine is a tetravalent vaccine, so in addition to H3N2 influenza A, it will protect against another subtype of influenza A (H1N1) and two different lineages of influenza B virus. These viruses do not change as quickly. like H3N2, so the vaccine is more likely to provide better protection against these other flu viruses.
Even if the protection of the H3N2 vaccine is lower than usual this year, the vaccine could make the difference between recovering at home and ending up in hospital.
Read more: Which Flu Vaccine Should I Choose? And what are cell-based and “adjuvant” vaccines?
So who should get the flu shot and when?
The flu vaccine offers the highest level of protection for the first three to four months after vaccination. In general, the season reaches its peak between June and September, although this year we have seen a start much earlier than usual for the flu season. It is unclear whether this early start will mean a longer flu season or an early end. So it’s not too late to get vaccinated.
Influenza vaccines are recommended for all people six months of age or older, but are especially important for people who are most at risk for complications from the flu, such as:
- Aboriginal and islanders in the Torres Strait six months and older
- children from six months to five years
- pregnant woman
- people 65 and older
- people six months of age or older who have medical conditions that put them at greater risk for serious illness.
What if you still have the flu?
If you develop flu symptoms, isolate yourself and consult your GP for a flu PCR test to determine if you are actually infected with the flu, especially if you are in the highest risk groups.
Influenza-specific antivirals can help, if given early. To ensure quick access for particularly vulnerable elderly care residents, care facilities for the elderly are being provided with the antiviral drug of the flu Tamiflu.
In New South Wales, free clinics now offer tests for the flu, respiratory syncytial virus (RSV) and SARS-CoV-2, the virus that causes COVID. Other states and territories may follow.