Those who already have Norovirus, winter vomiting bug, may be at risk of re -catching it in this season, says experts in the UK’s Health Protection Agency.

Data suggests that a different stress of the virus is increasing and having a stress does not necessarily protect you from catching the other, they recommend.

Norovirus can be particularly serious for young children, large adults and people with weak immune systems.

The cases are still “exceptionally high”, which are more than twice the five-season-average for this time of the year, the latest figure show.

Amy Douglas, the leading epidemicist at the UKHSA, said the biggest impact was being seen in hospitals and care houses.

He said, “With many genotypes spreading at the same time, people can get infected more than once this season,” he said.

The cases are partially more than expected due to the emergence of the recent stress of the virus called gii.17, but also due to the better ways of testing for the virus.

Now data shows that a separate, but more commonly seen stress is increasing.

This means that people who already have bugs can catch it again because having a version of the virus does not protect you completely against the other.

There is no suggestion that either stress leads to a more serious illness than expected.

Norovirus cases usually begin to decrease with the heat of the weather, but the UKHSA says it is to work soon whether the cases are at the peak.

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

Symptoms of Norovirus include:

• nausea and vomiting
• Diarrhea
• Fever
• Abdominal pain
• Obtain organs

If you think you may have Norovirus, experts recommend:

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

Many domestic disinfectants do not work well against viruses. Nor alcohol hand gels.

If you are worried – for example if a small child is not able to keep the fluid down or the disease does not stop after a few days – make sure you seek medical advice

Do not visit hospitals and care houses or prepare food for others, until 48 hours after the symptoms are closed.