People who are infected with both coronavirus and flu have a serious increased risk of death, Public Health England has warned.
A study performed during the first wave of the pandemic suggests that those suffering from co-infection had a risk of death that was six times greater than the general population.
Figures show 43% of those diagnosed with COVID-19 and flu died, compared with 27% of those who only tested positive for coronavirus.
Those who lost their lives tended to be older, Public Health England added.
Flu usually kills about 11,000 people a year in England and many more are hospitalised, prompting experts to warn that people should “not be complacent” this year.
Officials have warned that both influenza and COVID-19 could be circulating at the same time, and are urging people who are eligible to get a flu vaccine.
The vaccination programme has been expanded this year, meaning up to 30 million people in England will be eligible.
According to experts, those who are more susceptible to the effects of flu are also more at risk from COVID-19.
PHE’s medical director Professor Yvonne Doyle said flu is an “extremely unpleasant condition” – and some Britons are mistaken in thinking that it is just like a cold.
Stressing flu can be fatal and that the vaccine is safe, she added: “If you get both [flu and coronavirus], you are in serious trouble.
“The people who are most likely to get both of these infections may be the very people who can least afford to in terms of their own immune system or their risk for serious outcomes.
“Please protect yourself against flu this year.”
Those eligible for the flu vaccine include primary school children, those aged 65 and over, people with long-term health conditions and pregnant women.