People infected with both flu and Covid-19 are more than twice as likely to die as someone with the new coronavirus alone, a new study has shown.
An analysis by Public Health England (PHE) of cases from January to April 2020 also found that people with the two viruses were more at risk of severe illness.
Most cases of co-infection were in older people, and more than half of them died, the study found.
The data has been released following the launch of Wales’ largest ever flu vaccination programme which aims to ease pressure on hospitals during the winter.
Many people are eligible to receive a free flu vaccine every year, but many more groups have been added to the list amid the Covid-19 pandemic.
Jonathan Van-Tam, England’s deputy chief medical officer, told a PHE media briefing: “There is now some emerging evidence which clearly suggests that co-infection with influenza and Covid-19 produces bad outcomes. One of these diseases is currently vaccine preventable, and that’s the really important point.”
PHE’s study looked at 19,256 people who were tested for both flu and Covid-19 from January 20 to April 25 this year.
It found 58 people with co-infection, among whom the death rate was 43.1% (25). Of those who died, 80% (20) were aged over 70.
The odds of death were 2.27 times as high when compared with people who had the new coronavirus alone, and were 5.92 times higher than in people with neither flu nor Covid-19.
The authors said that this suggested “possible synergistic effects” in co-infected people.
In addition, the risk of testing positive for Covid-19 was 68% lower among flu positive cases. PHE said that this was consistent with recent findings from New York where under 3% of people testing positive for Covid-19 had coinfection with flu, whereas 13% of those testing negative for Covid-19 were flu positive.
PHE said longstanding evidence showed that being infected with one respiratory virus meant that people were less likely to be infected with another in the short term.
But it said that more research was needed to understand the relation between flu and Covid-19 because flu came early last winter, so the two did not overlap much.
Yvonne Doyle, medical director of PHE, told the briefing: “There is some evidence to suggest that flu and Covid and other viruses may compete with each other.
“[But] if you get both, you are in some serious trouble. And the people who are most likely to get both may be the very people that can least afford to.”
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Ms Doyle said that PHE’s data provided “an important signal” about the need for people to protect themselves against flu this year.
She said: “Most of the [other] studies on flu and Covid are case reports and may be subject to publication bias, but this particular piece of work looked at death records, hospitalisation records, and infection records from laboratories. So, we are pretty confident that it reflects what actually had happened.
“This campaign will reinforce the importance of taking flu seriously this year and not being complacent about that.”
In Wales, pregnant women, people with long-term health conditions, those aged over 65, carers and those in shielded groups will be able to access a free flu vaccination this winter.
These people can get their vaccine at their GP surgery or via a community pharmacy.
Similarly, children aged two and three years old on August 31, 2020 are eligible for a flu vaccine this year. Children in primary school from reception class to year 6 (inclusive) are also eligible.
They are all offered the nasal spray vaccine which is a fine mist squirted up the nose.
Children from six months but under two years old with a long-term health condition are offered a flu vaccine by injection.
Parents can check if their child is eligible for a flu vaccine this autumn by using this flu vaccine checker.
Further information is available on the Public Health Wales website.
Health and social care workers can also get the jab.