After two years of being virtually gone, the flu is back, sweeping Australia — and the world.
This year there are more than 15,000 flu cases in New South Wales alone, more than 12,000 of which have been diagnosed since early May.
The Queensland government has announced free flu vaccinations and NSW is considering doing the same. The president of the Australian Medical Association, Omar Khorshid, has insisted the incoming federal government to provide free flu shots for all Australians.
In the meantime, COVID cases continue to increase as the weather gets colder.
The good news is that we know that the flu vaccine can protect against the flu — and a growing body of international research suggests that the flu shot may also protect against COVID.
A recent study of 30,774 health workers in Qatar found flu vaccine may protect against COVIDparticularly serious illness.
These promising results have implications not only for COVID, but also for future pandemics caused by newly emerging germs. However, there are some reasons for caution.
New flu findings
the Qatar studyReleased online this month and yet independently verified, it used data from more than 12,000 health professionals who had a COVID test during the 2020 flu season.
The researchers compared flu vaccination rates between the 576 health care workers who contracted COVID, and a comparable group of 2,000 health care workers who tested negative for COVID in the last three months of 2020.
Those who had a flu vaccination at least two weeks before the COVID test were 30% less likely to have a positive COVID test and nearly 90% less likely to develop severe or critical COVID, compared to those who had not recently had the flu were vaccinated.
This finding is consistent with comparable retrospective studies from Brazil, Italy, Iran, the Netherlands and the United States, which have also shown protective effects of flu vaccination against COVID.
Common to studies of people who work in the health sector is the risk that people in the study are health-conscious. It is likely that they are more likely to follow COVID protection advice, such as complying with lockdowns, physical isolation and wearing masks. They are also more likely to get their flu vaccination. This potential bias is reduced in the Qatar study by focusing only on health professionals, but it cannot be ruled out that it contributes to the findings.
There are two further considerations to the implications of this study. First, the health professionals who participated in the study were young and not assessed to see if they had other health problems. This means that the effects seen in the study may not apply to the elderly and those with other health conditions — both of which are at greater risk for severe COVID.
Second, the study used data collected before COVID vaccines and before COVID variants such as Omicron. This means that the impact of the findings in current global conditions is unclear.
In the study, the average time for COVID testing after flu vaccination was six weeks. Since the study only uses data over a three-month period, it’s unclear whether this protective effect of the flu vaccine against COVID can last for more than a few months.
Favorable ‘off-target’ effects of vaccines
In the early months of the pandemic — while COVID vaccines were still in development — researchers were intensely interested in the possibility that existing vaccines could provide some protection against SARS-CoV-2 (the virus that causes COVID).
This is due to emerging evidence that some vaccines may have additional beneficial effects beyond just protecting against the infection they were originally designed for.
This bonus protection is usually linked to live attenuated vaccines, made from an attenuated form of the germ or a related germ. For example, both the 100-year-old Bacille Calmette-Guérin (BCG) tuberculosis vaccine and the measles vaccine have been shown to reduce the number of infants. deaths from any cause†
This protection is believed to be because these vaccines can kick-start the immune system so that it protects the body more effectively against infectious diseases.
To learn more about the bonus protection of routine vaccines like this one against COVID, multiple randomized controlled trials are underway.
A multinational clinical trial called the BRACE trial, has enrolled nearly 7,000 health professionals to determine whether the BCG vaccine reduces the incidence of symptomatic and severe COVID. So far we have found BCG vaccination alters immune response to SARS-CoV-2 in a way that could reduce severe COVID disease.
However, this trial is ongoing and we must wait for the final results to determine whether this immune response translates into true protection against COVID.
Reducing the inflammatory response of COVID?
For flu vaccines, a plausible explanation for their protective effect against COVID is that flu vaccination reduces the risk of co-infection with flu and SARS-CoV-2.
Co-infection with flu and COVID is associated with a more serious disease. Preventing this could reduce the severity of COVID. However, due to the exceptionally low flu rates in Qatar during the 2020 flu season, this is unlikely to explain the recent findings.
Like the BCG vaccine, flu vaccines can potentially reduce harmfulness inflammatory immune responses to SARS-CoV-2 infection. Severe COVID has been linked to overactive inflammatory responses that can cause tissue damage and cause severe symptoms. By reducing inflammation, these routine vaccines can prevent related tissue damage.
These promising results are emerging as we grapple with growing COVID cases and the pandemic continues.
More research is needed to confirm what researchers are starting to report. But the potential of existing vaccines, such as the flu shot and BCG, to protect against COVID raises the possibility that they could also help protect against future pandemics.
As exciting as these new results are, the best evidence remains that flu vaccination protects us from flu and COVID vaccination and boosters protect against COVID and serious illness.
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