After virtually gone for two years, the flu has returned and is spreading rapidly across Australia and the world.
So far this year, there have been more than 15,000 cases of influenza in New South Wales alone, of which more than 12,000 have been diagnosed since early May.
The Queensland government has announced free flu shots and NSW is considering doing the same. The president of the Australian Medical Association, Omar Khorshid, has urged the incoming federal government to offer free flu shots to all Australians.
Meanwhile, COVID cases continue to rise as the colder weather arrives.
The good news is that we know that the flu vaccine can protect against the flu, and a growing number of international research suggests that the flu vaccine could also protect against COVID.
A recent study of 30,774 health workers in Qatar found that the flu vaccine could protect against COVID, especially serious diseases.
These promising results have implications not only for COVID, but also for future pandemics caused by emerging germs. However, there are some reasons for caution.
Read more: Should I Get the 2022 Flu Vaccine? And how effective is it?
New flu findings
The Qatar study, published online this month and not yet independently verified, used data from more than 12,000 health workers who were tested for COVID during the 2020 flu season.
The researchers compared influenza vaccination rates among the 576 health workers who had COVID and a similar group of 2,000 health workers who had tested negative for COVID in the last three months of 2020.
Those who were vaccinated against the flu at least two weeks before COVID testing were 30% less likely to have a positive COVID test and almost 90% less likely to develop severe or critical COVID. they had not recently been vaccinated against the flu.
This finding is consistent with similar retrospective studies in Brazil, Italy, Iran, the Netherlands, and the United States, which have also shown protective effects of influenza vaccination against COVID.
Common to the studies of people working in the field of health, there is a risk that the people in the study will be aware of health. They are more likely to follow COVID’s protective advice, such as complying with confinement, physical isolation, and the use of masks. They are also more likely to get vaccinated against the flu. This potential bias is reduced to the Qatar study by focusing only on health workers, but it cannot be ruled out that it contributes to the findings.
There are two more considerations about the implications of this study. First, the health professionals included in the study were young and were not evaluated for other health conditions. This means that the effects observed in the study may not be true for the elderly and those with other health problems, both of whom are at higher 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 on current global circumstances is unclear.
In the study, the average time for COVID testing after the flu shot was six weeks. With the study using data only for a period of three months, it is unclear whether this protective effect of the influenza vaccine against COVID can last beyond a few months.
Benefits “off-target” effects of vaccines
In the early months of the pandemic, while COVID vaccines were still in development, researchers were keenly interested in the possibility that existing vaccines might offer some protection against SARS-CoV-2 (the virus that causes COVID).
This is due to the emerging evidence that some vaccines may have additional beneficial effects, rather than just protecting against the infection for which they were originally designed.
This additional protection has been mainly related to live attenuated vaccines, made from a weakened form of the germ or a related germ. For example, both the 100-year-old TB vaccine called Bacille Calmette-Guérin (BCG) and measles vaccines have been shown to reduce infant deaths from any cause.
This protection is believed to be due to the fact that these vaccines can activate the immune system because it protects the body more effectively from infectious diseases.
To understand more about the additional protection of routine vaccines like these against VOCID, several randomized controlled trials are being conducted.
A multinational clinical trial, called the BRACE trial, has enrolled nearly 7,000 health care workers to determine if the BCG vaccine reduces the incidence of symptomatic and severe COVID. To date, we have found that BCG vaccination changes the 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 real-world protection against VOCID.
More research is needed, but there may be additional benefits to catching the flu. Shutterstock
Read more: Cases are high and winter is approaching. We must stop ignoring COVID
Decrease the inflammatory response of VOCID?
For influenza vaccines, a plausible explanation for its protective effect against COVID is that influenza vaccination reduces the risk of having the flu and SARS-CoV-2 infection at the same time.
Co-infection with influenza and VOCID is associated with a more serious illness. 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 recent findings.
Like the BCG vaccine, influenza vaccines may decrease potentially harmful inflammatory immune responses to SARS-CoV-2 infection. Severe COVID has been linked to hyperactive inflammatory responses that can cause tissue damage and cause severe symptoms. By reducing inflammation, these routine vaccines could prevent related tissue damage.
Future protection
These promising results emerge as we deal with the growth of COVID cases and the ongoing pandemic.
More research is needed to confirm what researchers are beginning to report. But the potential of existing vaccines, such as the flu vaccine and BCG, to provide protection against VOCID raises the possibility that they may also help protect against future pandemics.
As exciting as these new results may be, the best evidence remains that the flu vaccine protects us from the flu and the VOCID vaccination and reinforcements protect us against VOCID and serious illness.
Read more: Flu, COVID and Flurone: What We Can and Can’t Expect This Winter