A mutated strain of meningitis B may been the “main driver” of the Kent outbreak, the UK Health Security Agency (UKHSA) has said. A technical briefing published on Tuesday outlined the results of preliminary analysis of the bacteria which led to a sudden surge in cases and the deaths of two young people.

The report said: “It is a realistic possibility that the outbreak strain is the main driver of the outbreak. At a minimum it is likely to be contributing.” The number of cases under investigation in the outbreak fell for a second day yesterday, after meningitis was ruled out in six previously suspected cases. The total now stands at 23 cases, 20 of which have been confirmed through laboratory testing.

No new cases were identified for a second consecutive day, raising hopes that the outbreak has peaked.

The UKHSA’s analysis found that the outbreak had been caused by a strain of a “recently emerged subtype” of meningitis B which has been present in England since 2020.

However, experts found there may have been some mutations in that subtype which were specific to this outbreak.

These are now being evaluated to help officials understand how they may change the behaviour of the bacteria.

Other factors that may have contributed to the explosive spread include close contact between young people in Kent — particularly those attending the Club Chemistry nightclub.

NHS Kent and Medway said that, as of 11am on March 24, 13,386 doses of antibiotics and 10,627 vaccines had been given out.

Professor Robin May, the UKHSA’s chief scientific officer, said: “This preliminary analysis offers strong reassurance that our existing vaccinations and antibiotic treatment offer will be effective against this strain.

“In collaboration with the research community, we will continue intensive laboratory investigations of the strain to determine how the spread of the outbreak may have been influenced by the bacterial strain, social or environmental conditions, and population immunity.”

The meningitis B vaccination programme is being expanded to include Year 11 pupils at schools affected by the outbreak in Kent.