After nearly becoming extinct for two years, influenza has resurfaced and is rapidly spreading over Australia and the rest of the world. There have been over 15,000 cases of influenza in New South Wales alone this year, with over 12,000 cases identified since the beginning of May.

Queensland has agreed to provide free influenza vaccinations, while New South Wales is considering similar legislation. The president of the Australian Medical Association, Omar Khorshid, has proposed that the next federal government provide free flu shots to all Australians. COVID cases continue to rise as the temperature drops. The good news is that we know the flu vaccine can protect against it, and growing data suggests it may also protect against COVID.

A recent study of 30,774 Qatari healthcare professionals discovered that an influenza vaccine could protect against COVID, especially the most severe kind. These promising findings have ramifications not only for COVID but also for future pandemics caused by newly discovered diseases. However, there are various reasons to be cautious.

The Qatar study, which was published online this month but has yet to be independently confirmed, looked at data from approximately 12,000 healthcare professionals who had a COVID test during the 2020 flu season. The researchers compared the influenza vaccination rates of 576 COVID-infected healthcare workers to a similar sample of 2,000 COVID-negative healthcare professionals in the final three months of 2020.

Those who had an influenza vaccination at least two weeks before COVID testing were 30% less likely to have a positive COVID test and nearly 90% less likely to have severe or critical COVID. This finding is in line with recent retrospective studies from Brazil, Italy, Iran, the Netherlands, and the United States that demonstrate influenza immunization protects against COVID.

The study participants may be health-conscious, as is usual in research involving people working in the health industry. They are more likely to follow COVID protection guidelines such as lockdowns, physical isolation, and mask use. They are also more likely to have received an influenza vaccination. The Qatar study mitigates this potential bias by focusing on healthcare workers, albeit it cannot be fully excluded as a factor in the findings. 

Consider two more implications of this research. First, the study’s healthcare professionals were young and had not been examined for health risks. As a result, the findings of this study may not apply to older people or those with other health concerns, both of which are at a higher risk of severe COVID.

Second, the study used data collected before the release of COVID vaccinations and COVID variants such as Omicron. This suggests that the significance of the findings in the current global context is unknown. On average, six weeks elapsed between COVID testing and the influenza vaccine in the research. Because of the three-month data collection timeframe, it is unknown whether the flu vaccine’s COVID preventative advantage will last more than a few months.

While COVID vaccines were still being created in the early months of the pandemic, researchers were keen to see if existing vaccines might provide some protection against SARS-CoV-2 (the virus that causes COVID). This is due to mounting data demonstrating that some vaccines have benefits beyond simply protecting against the infection for which they were originally designed.

This improved protection has mostly been attributed to live-attenuated vaccinations, which are made up of weakened copies of the pathogen or a related pathogen. The 100-year-old tuberculosis immunization, Bacillus Calmette-Guérin (BCG) and measles vaccines, for example, have been found to reduce infant death from any cause. This protection is thought to be related to the fact that these vaccines can enhance the immune system, allowing the body to more effectively defend itself against infectious diseases.

Multiple randomized controlled trials are presently underway to learn more about the increased protection provided by routine COVID immunizations like these. Over 7,000 healthcare personnel have participated in the global clinical trial BRACE to see if the BCG vaccine reduces the occurrence of symptomatic and severe COVID. So far, it has been established that BCG vaccination alters the immune response to SARS-CoV-2, potentially lowering the severity of COVID disease.

However, this study is still ongoing, and we must wait for the full results to determine whether this immune response translates into COVID protection in the real world. One possible reason for the protective effect of influenza vaccines against COVID is that influenza vaccination reduces the likelihood of contracting both influenza and SARS-CoV-2 at the same time.

Infection with both influenza and COVID is associated with more severe disease. COVID severity may be reduced if this is avoided. This hypothesis is unlikely to account for the recent findings because influenza rates in Qatar were relatively low during the influenza season of 2020.

Influenza vaccines, notably the BCG vaccine, have been shown to prevent potentially harmful inflammatory immune responses to SARS-CoV-2 infection. Severe COVID has been linked to hyperactive inflammatory responses, which can cause tissue damage and severe symptoms. By lowering inflammation, these frequent vaccines may help to avoid tissue damage. These optimistic results come as the number of COVID patients continues to climb as a result of the epidemic.

More research is needed to back up the current research consensus. However, the capacity of existing immunizations, such as the flu vaccine and BCG, to provide COVID protection raises the possibility that they could contribute to future pandemic defense. Regardless of how intriguing these new findings are, the best available evidence indicates that influenza vaccination protects against influenza, whereas COVID immunization and boosters protect against COVID and severe disease.

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