The city council says it is working with the UK Health Security Agency and other local schools after the new, more transmissible strain was found at Solent Infant School.
Helen Atkinson, Portsmouth City Council's director of public health, said: ‘Following the confirmation of a case of the Omicron variant at Solent Infant School, we are working closely with the UKHSA and both Solent Infant and Junior School to monitor the situation.
‘Close contacts will be contacted by NHS Test and Trace and advised of next steps. The school has also introduced additional precautionary measures to prevent further spread in the school community.
‘Omicron is a new variant of coronavirus and early signs indicate that it is highly transmissible. All the current prevention measures we are asked to follow for Covid-19 remain the best protection our residents can take.
‘We encourage everyone to remember the safe behaviours to prevent further spread. Get vaccinated if eligible - first dose, second dose, booster. Continue with regular testing, even if not showing symptoms. Wear face coverings in indoor crowded settings and in shops and public transport in line with government guidance. Self-isolate immediately and book a PCR test if you have symptoms. Every little action helps to keep yourself, your loved ones and your communities safe.’
Wednesday saw the first case of Omicron confirmed in Portsmouth, with the UKHSA saying it was linked to travel, although health bosses said they suspected that it would already be in the community. Later that day the Prime Minister Boris Johnson brought in the so-called Plan B measures for the UK to reduce transmission.