People who are vaccinated against influenza may be partly protected against some of the severe effects of coronavirus, and be less likely to need emergency care, according to a major study.
The analysis of nearly 75,000 Covid patients found significant reductions in stroke, deep vein thrombosis (DVT) and sepsis, and fewer admissions to emergency departments and intensive care units, among those who had been given the flu jab.
While the flu vaccine did not reduce Covid deaths in the study, previous research suggests the jab may provide some protection against coronavirus by boosting the innate immune system – the body’s general defences that are not targeted against a particular pathogen.
Another explanation is possible: patients who had the flu vaccine may have been in better general health than those who went without, and while the researchers tried to take this into account, such adjustments are not easy.
"We detected an association that appears to show flu vaccination offers some protection against severe Covid-19 disease," said Devinder Singh, a senior author on the study and professor of clinical surgery at the University of Miami.
If the findings are backed up by further studies, they may be most valuable to countries that have not been able to compete with wealthier nations for Covid vaccines, and where the burden of flu and coronavirus combined threaten to overstretch health services.
“It’s very important to emphasise that we absolutely recommend the Covid-19 vaccine, and in no way suggest the flu vaccine is a substitute to the proper Covid-19 vaccine,” Prof Singh said.
The researchers compared the electronic health records of 37,377 Covid patients from the UK, the US and elsewhere, who had received flu jabs with those from the same number of Covid patients who had not been vaccinated against flu. The patients in the two groups were closely matched for age, sex, ethnicity, health problems including diabetes and lung disease, and lifestyle factors such as diet and whether or not they smoked.
The scientists analysed how often the patients suffered any of 15 potentially serious health effects ranging from blood clots and heart attacks to kidney and respiratory failure in the four months following their Covid diagnosis.
The findings, presented at an online meeting of the European Society of Clinical Microbiology and Infectious Diseases, suggest the flu vaccine may protect against some medical problems caused by Covid. According to the study, Covid patients who were not vaccinated against the flu were 45 per cent to 58 per cent more likely to have a stroke, about 40 per cent more likely to develop DVT, and 36 per cent to 45 per cent more likely to have sepsis. They were also more likely to be admitted to an intensive care unit and to have more frequent visits to hospital emergency departments.
"It could be that the flu vaccine stimulates the immune system non-specifically and has that benefit, but you always wonder whether these associations are causal, or whether there's a common factor, like social deprivation which might explain why they go hand in hand," said Prof Peter Openshaw, a member of the British government's New and Emerging Respiratory Virus Threats Advisory Group (Nervtag). "People who manage to get a flu vaccine may have better health in other ways."
“The best way to protect yourself from Covid is to get a Covid vaccine,” he added.
In the UK, the NHS is preparing from September to offer Covid booster shots alongside annual flu vaccines, after the Joint Committee on Vaccination and Immunisation there issued interim advice.
British ministers are particularly concerned that influenza, which was almost nonexistent last season, will bounce back dangerously in the winter ahead, just as Covid cases peak again.
"One of the big risks that I and others were worried about is in a bad flu season, you could see 20,000 people dying," the vaccines minister Nadhim Zahawi told The Andrew Marr Show on the BBC. – Guardian