Doctors have warned that it is important you are aware of a killer virus - and you probably won't have heard of before.
Human metapneumovirus (HMPV) is a virus that may not be on everyone's radar.
It has the same symptoms as Covid and the flu - causing cough, runny nose or nasal congestion - and is on the rise.
Studies have shown that over the last four years HMPV was just as common as respiratory syncytial virus (RSV) and flu in pensioners in hospital.
HMPV, which can cause killer pneumonia, and it was the second most common cause of respiratory infections in kids behind RSV in the last 25 years.
Dr John Williams, a paediatrician at the University of Pittsburgh, Pennsylvania, fears that people are not aware of this fatal virus.
He said: "It's the most important virus you've never heard of.
"Those are the three major viruses. Those are the big three in kids and adults, the most likely to put people in the hospital and cause severe disease, most likely to sweep through nursing homes and make older people really sick and even kill them."
Worryingly, most people who catch HMPV have no idea as testing outside of hospitals is rare.
Symptoms of the virus include a runny nose, sore throat, cough and wheezing.
More severely, it can cause wheezing, difficulty breathing, hoarseness, cough, pneumonia; and in adults, aggravation of asthma, also has been reported.
Most people recover within about seven to 10 days.
However, people with weakened immune systems, asthma, or respiratory conditions may develop serious illness, such as bronchitis or pneumonia.
