Adults in hospitals who have Covid-19 and the flu at the same time are at much greater risk of severe disease and death compared with patients who have Covid-19 alone or are infected with other viruses, according to a new study published in the Lancet.
However, Indians can heave a sigh of relief. The Indian Council of Medical Research (ICMR) has claimed in a separate study that in India such cases are rare and mostly low risk. The study — by experts from ICMR, New Delhi, and the Pune-based National Institute of Virology — found only five cases of influenza-SARS-CoV-2 co-infections among 13,467 people with flu symptoms and respiratory infections it analyzed from July 2021, to January 2022; a prevalence of 0.04%.
In contrast, the Lancet study has found that patients with co-infection of SARS-CoV-2, which causes Covid-19, and influenza viruses were over four times more likely to require ventilation support and 2.4 times more likely to die than if they only had Covid-19, experts found.
Researchers say the findings show the need for greater flu testing of COVID-19 patients in hospitals and highlight the importance of full vaccination against both Covid-19 and the flu.
The team from the University of Edinburgh, University of Liverpool, Leiden University, and Imperial College London, made the findings in a study of more than 305,000 hospitalized patients with COVID-19.
The research—delivered as part of the International Severe Acute Respiratory and emerging Infection Consortium's (ISARIC) Coronavirus Clinical Characterisation Consortium—is the largest ever study of people with Covid-19 and other endemic respiratory viruses.
The team looked at the data of adults who had been hospitalized with Covid-19 in the UK between 6 February 2020 and 8 December 2021.
Test results for respiratory viral co-infections were recorded for 6965 patients with COVID-19. Some 227 of these also had the influenza virus, and they experienced significantly more severe outcomes.
Dr. Maaike Swets, Ph.D. student at the University of Edinburgh and Leiden University, said: "In the last two years we have frequently witnessed patients with COVID-19 become severely ill, at times leading to ICU admission and the employment of an artificial ventilator to help with breathing. That an influenza infection could give rise to a similar situation was already known, but less was understood about the outcomes of a double infection of SARS-CoV-2 and other respiratory viruses."
Professor Kenneth Baillie, Professor of Experimental Medicine at the University of Edinburgh, said: "We found that the combination of COVID-19 and flu viruses is particularly dangerous. This will be important as many countries decrease the use of social distancing and containment measures. We expect that COVID-19 will circulate with flu, increasing the chance of co-infections. That is why we should change our testing strategy for COVID-19 patients in hospitals and test for flu much more widely."
Professor Calum Semple, Professor of Outbreak Medicine and Child Health at the University of Liverpool, said: "We are seeing a rise in the usual seasonal respiratory viruses as people return to normal mixing. So, we can expect the flu to be circulating alongside COVID-19 this winter. We were surprised that the risk of death more than doubled when people were infected by both flu and COVID-19 viruses. It is now very important that people get fully vaccinated and boosted against both viruses, and not leave it until it is too late."
