One person in the UK has been infected by a strain of flu similar to viruses spreading in pigs, health officials have announced.

But what is the strain, what are the symptoms in humans and are experts worried?

Here’s what we know so far.

What is the virus?

Influenza A(H1) viruses are native to swine populations in most regions of the world, but viruses in pigs can occasionally infect humans, usually after direct or indirect exposure to pigs or contaminated environments.

Influenza A(H1N2)v is similar to flu viruses currently circulating in pigs in the UK – but this is the first detection of this particular strain of flu in a human in the UK.

Has the strain been found in humans before?

There’s been a total of 50 human cases of influenza A(H1N2)v reported globally since 2005, but no human deaths from this strain have been reported.

Human infections with swine influenza viruses – also known as swine flu – “occur sporadically”, according to the UK’s Health Security Agency (UKHSA). It becomes a “variant influenza virus” when detected in a person.

The infection found in the UK is slightly different from recent human cases of the flu strain globally, health officials say, but similar to viruses in UK pigs.

How was it detected in the UK and what are the symptoms?

The case was detected as part of routine national flu surveillance undertaken by UKHSA and the Royal College of General Practitioners.
The individual was tested by their GP after experiencing respiratory symptoms and influenza A(H1N2)v virus was detected. They experienced a mild illness and have fully recovered.

Is it the same swine flu as 2009?

In 2009, there was a pandemic in humans caused by an influenza virus (official name: influenza A H1N1(pdm09)) commonly referred to as “swine flu”.

But that virus contained genetic material from viruses circulating in pigs, birds and humans in the 1990s and 2000s. It’s now circulating in humans on a seasonal basis and is no longer referred to as swine flu.

It is distinct from the viruses currently circulating in pigs. The case of flu found in the UK is classed as swine flu because it’s influenza from a pig, but what was previously called swine flu in 2009 is now not referred to as that.

What happens next and are experts worried?

The source of the individual’s infection has not yet been found and remains under investigation, but close contacts of the case are being followed up by the UKHSA and partner organisations, and will be offered testing and advised on any necessary further care if they have symptoms or test positive.

The UK’s Chief Veterinary Officer, Dr Christine Middlemiss, said: “In this case we are providing specialist veterinary and scientific knowledge to support the UKHSA investigation.

“Pig keepers must also report any suspicion of swine flu in their herds to their local vet immediately.”

People who are contacted and asked to test are encouraged to do so in order to assist in the detection of cases and assessment of transmission.

Those with any respiratory symptoms should continue to follow the existing guidance, including avoiding contact with other people while symptoms persist, particularly if the people they are coming into contact with are elderly or have existing medical conditions.

Martin Michaelis, professor of molecular medicine at the University of Kent, told FactCheck that as the pig influenza case detected in the UK was “mild” and efforts are ongoing to “trace and break potential transmission chains,” it “does not seem very likely that this could be the beginning of a large, dangerous pig influenza outbreak in humans”.

However, he added that “you can never be entirely sure, because mutations can happen that change the nature of this virus strain, if it keeps spreading in humans”.

But he noted that “this pig H1N2 influenza virus infection of a human is a stark reminder that influenza viruses that spread between different species are posing a continuous risk to humans”.

Paul Hunter, professor in medicine at the University of East Anglia, told the Science Media Centre: “Overall the evidence is that influenza A(H1N2) does not cause any more severe disease than other more commonly circulating types of influenza.

“Also, person to person transmission does not appear to be very efficient and sustained person to person transmission has not been reported so far.”