Flu shot linked to less severe COVID-19: Study

People who got a flu shot earlier this year may be less likely to suffer a severe COVID-19 infection down the road, according to new research.

The study, published in the journal Plos One on Wednesday, analyzed the electronic medical records of more than 74,700 people from the United States, the United Kingdom, Italy, Germany, Israel and Singapore, who tested positive for COVID-19. Researchers found that those who had gotten the flu vaccine during the previous six months were less likely to have had health complications related to their COVID-19 infection.

Specifically, researchers found that those who didn't get flu shots were up to 20% more likely to be admitted to the ICU; up to 58% more likely to visit the emergency room; up to 45% more likely to develop sepsis; up to 58% more likely to have a stroke; and 40% more likely to develop deep vein thrombosis, compared with those vaccinated against the flu.

Researchers didn't find any connection between receiving a flu shot and being less likely to die from COVID-19.

The new research is in line with several previous studies that found links between better COVID-19 outcomes and flu shots. That prior research similarly didn't find the flu vaccine offered any protection against COVID-19 death.

Importantly, the flu shot's link to better COVID-19 outcomes doesn't necessarily mean it's protective against the novel coronavirus. While it's possible that the flu shot boosts immunity, it's also possible that people who opt to get the flu shot tend to be healthier overall than people who skip it, meaning they're already at lower risk for COVID-19 complications.

Additionally, the flu shot changes every flu season, so it's unclear whether the vaccine developed for the 2020-2021 flu season would have the same link to less severe COVID-19 that the 2019-2020 vaccine did.

Another key limitation with electronic medical records is that different countries may report symptoms differently and use different diagnostic tests to confirm SARS-CoV-2 diagnoses, which could skew the data.

While more research is needed, the study authors noted, "Even patients who have already received SARS-CoV-2 vaccination may stand to benefit given that the SARS-CoV-2 vaccine does not convey complete immunity."

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ABC News' Alexis Carrington contributed to this report.