Children are turning up in doctors' clinics infected with as many as three different types of viruses, in what experts believe is the result of their immune systems being weakened from two years of COVID lockdowns and mask-wearing.

Medical staff have come to expect a surge in cases of flu and severe colds during the winter. 

But they are reporting that there is not the usual downturn as summer approaches - and they suspect it could be due to the strict pandemic practices.

Furthermore, some of common strains of the flu appear to have disappeared, flummoxing scientists.

Thomas Murray, an infection-control expert and associate professor of pediatrics at Yale, told The Washington Post on Monday that his team was seeing children with combinations of seven common viruses - adenovirus, rhinovirus, respiratory syncytial virus (RSV), human metapneumovirus, influenza and parainfluenza, as well as the coronavirus. 

Some children were admitted with two viruses and a few with three, he said.

'That's not typical for any time of year and certainly not typical in May and June,' he said.

CDC data obtained by DailyMail.com showed lower overall levels of influenza infections among young children - but an abnormal surge starting several weeks ago during the beginning of the summer months, normally a dead period for respiratory infections.

Other strange patterns have emerged.

The rhinovirus, known as the common cold, is normally not severe enough to send people to hospital - but now it is.

RSV normally tapers off in the warmer weather, as does the influenza, but they have not.

And the Yamagata strain of flu has not been seen since early 2020 - which researchers say could because it is extinct, or perhaps just dormant and waiting for the right moment to return.

'It's a massive natural experiment,' said Michael Mina, an epidemiologist and chief science officer at the digital health platform eMed, told the Post.