A case of the Omicron variant of coronavirus has been identified in Hertfordshire, the UK Health Security Agency (UKHSA) has said.

The person who tested positive for the new variant lives in Three Rivers district and they are among 22 confirmed cases in England so far.

The UKHSA says the individuals that have tested positive and their contacts are all isolating, adding work is underway to identify any links to travel to Southern Africa.

Targeted testing is also said to be taking place at locations where positive cases were likely to be infectious.

Other identified cases are in London (14), Buckinghamshire, and Essex, as well as in the East Midlands, South East and North West.

The exact location in Three Rivers has not been publicly reported at this time but populous areas within the district include Rickmansworth, Croxley Green, Abbots Langley, Leavesden, and South Oxhey.

Dr Jenny Harries, UKHSA chief executive, said: "It is very likely that we will find more cases (nationwide) over the coming days, as we are seeing in other countries globally and as we increase case detection through focused contact tracing.

"That’s why it’s critical that anyone with Covid-19 symptoms isolates and gets a PCR test immediately."

Scientists are concerned by the Omicron, or B.1.1.529 variant, because it has a high number of spike protein mutations, potentially changing the behaviour of the virus with regards to vaccines, treatments and transmissibility.

Dr Maria Van Kerkhove, Covid-19 technical lead at the World Health Organisation, said they expect to have more information about the transmissibility of Omicron "within days".

She added there is some indication that some of the patients are presenting with mild symptoms but says it is still early days - and reinforced the message to get vaccinated.

But with uncertainty around the new variant, face coverings have become mandatory again in England in settings like shops and on public transport.

The Government has also tightened the rules around PCR tests for travellers returning to the UK and introduced quarantine rules for people from high-risk countries.

And the Covid booster programme has been accelerated to help slow down the spread of the new Omicron variant.

Dr Harries said: "Following the change in advice from the Joint Committee on Vaccination and Immunisation earlier this week, a booster dose for everyone over 18 years is now recommended and will be available at a minimum of 3 months from your last primary course jab. Please take up this offer as soon as you are eligible to protect yourself, your families and your communities."

She added: "We are continuing our efforts to understand the effect of this variant on transmissibility, severe disease, mortality, antibody response and vaccine efficacy.

"Vaccination is critical to help us bolster our defences against this new variant – please get your first, second, third or booster jab without delay."

The Omicron variant is in addition to the Delta variant already circulating locally.

More than 450 Watford residents have tested positive for Covid-19 since November 22 with a further 482 in Three Rivers and 481 in Hertsmere, Public Health England data shows.