Study Results Show High Prevalence of COVID-19, Flu Co-Infections in 2021-2022 Season

Central Missouri saw a high prevalence of COVID-19 co-infections during the 2021-2022 flu season, with a monthly co-infection rate as high as 48% among individuals with COVID-19, according to investigators from the University of Missouri School of Medicine.¹

In the study, 462 patients at University of Missouri Health Care who tested positive for COVID-19 were also tested for influenza. Of those who were positive for COVID-19, 33% were also positive for influenza.¹

“Co-infection in our samples peaked in October 2021 at 48% when the Delta variant was dominant and reached the lowest point at 7.1% in January 2022 when the Omicron variant prevailed,” Henry Wan, PhD, professor of molecular microbiology and immunology, veterinary pathobiology, electrical engineering, and computer science, said in a statement.¹

Of the 462 individuals with COVID-19, 51% had the Delta variant, and 38% had the Omicron variant.¹

Nasal swabs were collected between October 1, 2022, and January 27, 2022, which included individuals who were in the emergency department, urgent care, and inpatient and outpatient.²

Three individuals received 2 swabs that were collected on different dates, and 1 individual had 2 swabs on the same day.

Investigators found that those who were infected with the Omicron variant and those who received at least 1 influenza vaccine during the 2020 through 2022 influenzas seasons were less likely to become co-infected with both COVID-19 and influenza.¹

Additionally, these individuals were less likely to be hospitalized.¹

“Despite low flu vaccine effectiveness for the 2021-2022 season, which was estimated at less than 16%, our study highlights the importance of influenza vaccinations, as they appear to not only offer some protection against influenza infections but importantly, against COVID-19 and flu co-infections,” Wan said.¹

It was reported that co-infection was not associated with clinical outcomes, including cardiac symptoms, gastrointestinal symptoms, hospitalizations, or respiratory symptoms.²

Future studies conducted among a more diverse population and in a wider geographic area should be used to determine the prevalence of overall COVID-19 and influenza co-infections, as well as the effectiveness of both COVID-19 and influenza vaccines, investigators said.¹

“Testing for both flu and COVID-19 viruses in patients experiencing symptoms of respiratory illness and vaccinations against both viruses should continue to be encouraged,” Wan said.¹

Study limitations included the single geographic population. Additionally, all individuals tested positive for COVID-19, but there were no individuals with just an influenza infection, so the effectiveness of both COVID-19 and influenza vaccinations against co-infections were unclear.²

Finally, because those who were included in the study were from a health care facility, they were more symptomatic, making them more likely to seek medical care compared with those who were asymptomatic.²

References

1. Study finds high prevalence of COVID-19 and flu co-infections during 2021-2022 flu season. News release. EurekAlert. November 2, 2022. Accessed November 10, 2022. https://www.eurekalert.org/news-releases/969721

2. Tang CY, Boftsi M, Staudt L, et al. SARS-CoV-2 and influenza co-infection: a cross-sectional study in central Missouri during the 2021-2022 influenza season. Virology. 2022;576:105-110. doi:10.1016/j.virol.2022.09.009