People who have already had norovirus, the winter vomiting bug, could be at risk of catching it again this season, experts from the the UK’s Health Security Agency say.

Data shows a different strain of the virus is on the rise and having had one strain doesn’t necessarily protect you from catching another, they advise.

Norovirus can be particularly severe for young children, older adults and people with weakened immune systems.

Cases are currently still “exceptionally high” with numbers at more than double the five-season-average for this time of year, latest figure show.

Amy Douglas, Lead Epidemiologist at the UKHSA, said the biggest impact was being seen in hospitals and care homes.

“With multiple genotypes spreading at the same time, people could end up getting infected more than once this season,” she added.

Cases have been higher than expected partly because of the emergence of a recent strain of the virus called GII.17, but also because of improved ways of testing for the virus.

Data now shows that a different, but more commonly seen strain, is on the rise.

This means people who have already had the bug could catch it again as having one version of the virus does not fully protect you against the other.

There is no suggestion that either strain leads to more severe illness than expected, however.

Norovirus cases usually starts to decline as the weather warms up, but the UKHSA says it is too soon to work out whether cases have peaked.

The total remains close to its record high, with an average of 1,134 patients a day in hospital with norovirus last week – down slightly on the previous week (1,160), but still nearly two and a half times that seen in the same period last year.

If you think you may have norovirus, experts advise:

• Stay at home and do not return to work or school until two days after the vomiting and diarrhoea has stopped
• Drink plenty of fluids
• Wash your hands regularly with soap and water

Many household disinfectants do not work well against the virus. Nor do alcohol hand gels.

If you are concerned – for example if a young child is not able to keep fluids down or the illness does not stop after a few days – make sure you seek medical advice

Do not visit hospitals and care homes or prepare food for others, until 48 hours after symptoms have stopped.