Health officials are urging parents to keep poorly children home from school and say adults should mask up if they have to go out while feeling unwell.
The warning from the UK Health Security Agency (UKHSA) comes as cases of flu, coronavirus and scarlet fever surge.
It also comes amid massive pressure on A&E units.
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The Royal College of Emergency Medicine says it believes December will have been the worst on record for hospital bed occupancy and emergency care delays.
Professor Susan Hopkins, Chief Medical Adviser at the UK Health Security Agency (UKHSA), said: “If your child is unwell and has a fever, they should stay home from school or nursery until they feel better and the fever has resolved.
“Adults should also try to stay home when unwell and if you do have to go out, wear a face covering. When unwell don’t visit healthcare settings or visit vulnerable people unless urgent.”
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She also urged parents to teach children to wash their hands with soap and warm water and catch coughs and sneezes in tissues to help stop illness spreading.
But some argue against mask-wearing. Quoted in the MailOnline, north London NHS GP, Radio and TV presenter and medical writer Renée Hoenderkamp said “We have never done this before Covid, don’t do it now.”