Flu infections are increasing in England as a new strain continues to cause outbreaks particularly among children.

Data on the H3N2 strain from Australia shows it has had its worst flu season on record and this is now expected to be the case in Britain as we head into our winter. Swab samples sent by the NHS to laboratories showed the flu positivity rate increased to 11.6%, up from 10.7% the previous week.

UKHSA data shows last week the overall weekly hospital admission rate for flu increased to 4.56 per 100,000 of the population. This was up from 3.39 the previous week.

Infections are nowhere near the seasonal peak yet but are well ahead of where they typically are at this time of year.

The new flu strain is causing more severe illness even in otherwise healthy people and doctors had warned H3N2 'can kill' because it has mutated to be particularly aggressive. The rate of intensive care admissions for flu was 0.12 per 100,000 last week, compared with 0.10 per 100,000 in the week before.

Vaccines still offer significant protection and often prevent serious illness. H3N2 symptoms are generally similar to those of other influenza strains but with a few key differences.

While many people will experience an unpleasant, but relatively mild illness, experts warn there is a higher risk of deadly complications such as sepsis with this strain. The Royal College of Paediatrics and Child Health (RCPCH) has warned H3N2 "can kill" in rare cases and has called on parents to give their children the flu vaccine nasal spray.

UKHSA estimates show that deaths from flu in England stood at 7,757 last winter compared to 3,555 the year before. Child deaths involving flu also increased from 34 to 53.

It comes after UKHSA's early season data showed vaccination remains best defence alongside good respiratory hygiene.

While it won't necessarily stop people catching flu it is highly effective at preventing serious illness. This season's vaccine is 70-75% effective at preventing hospital admission in children aged 2 to 17 years and 30-40% effective in adults.

What is H3N2?

Australia and Japan have both been hit hard by flu because the main new strain, called H3N2, has mutated to better escape immunity from previous vaccines. This is because it has mutated to be particularly aggressive.

On the surface of the virus particle there are two protein spikes called hemagglutinin (orange in main image) and neuraminidase (green). Haemagglutinin plays a role in attachment of the virus to human respiratory cells. Neuraminidase plays a role in releasing newly formed virus particles from an infected cell.

What are the symptoms?

All flu virus strains can cause a sudden onset of the following symptoms:

Fever/chills

Cough (often dry)

Sore throat

Runny or stuffy nose

Body and muscle aches

Headache

Fatigue/weakness

For H3N2 there is a tendency for the fever to be worse. Patients often experience a higher average body temperature and a greater likelihood of a high fever - above 38°C - compared to strains like H1N1.

How to tell the difference between a cold and flu

The main difference is that flu symptoms are more severe and come on more suddenly, including fever, chills, muscle aches, headaches, and fatigue. Cold symptoms are generally milder and tend to develop more slowly, with a runny or stuffy nose being more common. Colds usually don't lead to serious health problems, unlike the flu.

How can I avoid getting the flu?

The best way to prevent the flu is by getting an annual flu vaccine, but you can also prevent infection by practicing good hygiene like washing your hands often, avoiding touching your face, and covering your coughs and sneezes.

Other preventative measures include cleaning frequently touched surfaces and avoiding crowded areas when possible.

Who can get vaccinated?

Flu vaccines are available for everyone aged 65 and over, under 65s in clinical risk groups, pregnant women, care home residents and carers, close contacts of those who are immunosuppressed, frontline social care workers, and health and social care staff as well as children.

Covid-19 vaccinations are available to adults aged 75 and over, older adult care home residents, and people who are immunosuppressed.

Eligible adults can book an appointment to get their flu vaccine now via at their local pharmacy via the NHS App, GP practice, online at www.nhs.uk/bookflu or by calling 119.

Flu surge as new more dangerous H3N2 strain spreading