The meningitis outbreak in Kent was caused by a new variant with significant mutations that are likely to have impacted on how fast it spread, officials say.
The UK Health Security Agency has mapped the entire genome of the circulating bacteria and found mutations in an area known to affect transmissibility.
The group B meningococci is closely related to a variant that has been in the UK for around five years but has some potentially alarming differences.
In a technical document published today, the UKHSA admits it is a ‘realistic possibility’ that the strain is the ‘main driver’ of the outbreak, which has killed two people and left others critically ill in hospital.
Experts found the genome of the bacteria has ‘multiple potentially significant genetic differences when compared to the most closely related genomes’.
These are now being evaluated to help officials understand how they may change its behaviour.
The document says experts considered three things that may have caused the disease to spread at such an ‘unprecedented’ rate – the strain, immunity of the affected population, and social factors.
And it concludes: ‘Given the unusual nature of the outbreak, it is highly likely that all three factors are contributing.’
Students receiving vaccines and antibiotics from medical staff in the sports hall at the University of Kent campus in Canterbury
Cases of invasive meningococcal disease in Kent outbreak, by case category, outbreak bacterial subtype, attendance at Club Chemistry and date of onset
The laboratory analysis also offers ‘strong reassurance’ that the antibiotics and MenB vaccine being offered to at-risk groups will be effective against the strain.
It comes as the UKHSA announced the MenB vaccination catch-up programme will be expanded to include year 11 pupils at schools affected by the outbreak, which has been linked to ‘super-spreader’ events at the Club Chemistry nightclub in Canterbury, Kent, earlier this month.
The latest figures show the number of cases has once again fallen as more testing revealed some people were wrongly told they were infected.
As of 12.30pm on Monday, 20 cases of meningitis had been confirmed, with a further three under investigation, bringing the total to 23.
This was down from 29 on Sunday, when 20 cases were confirmed and a further nine were under investigation.
Officials started vaccinating University of Kent students on Wednesday March 18.
The following day, on a visit to the campus, Health Secretary Wes Streeting said the programme would be expanded to more people, including sixth form pupils at four schools with known or suspected cases of menB.
Ministers have now agreed to offer jabs to Year 11 pupils at these schools, the UKHSA said.
Students are seen queuing at the University of Kent where a MenB catch-up vaccination programme is being rolled-out
Network diagram of cases of invasive meningococcal disease in Kent outbreak, by case category, and showing key exposures
Officials said widening the programme is a precautionary measure to ensure longer-term protection.
As of lunchtime on Monday, 13,088 doses of antibiotics had been given out in Kent along with more than 10,000 vaccine doses.
The UKHSA also confirmed the cases have a median age of 19, and while the majority are in education, five are not students.
Most patients (87 per cent) attended Club Chemistry in Canterbury at least once between March 5 and 7 before becoming unwell.
Most of those were students, and the three cases who did not go to the nightclub are all University of Kent students living in halls with links to those who did attend.
The earliest known case became unwell on March 9, and the latest on March 16.
According to the UKHSA, the peak of the outbreak – with the largest number of cases reported – was on March 13.
Professor Robin May, chief scientific officer at UKHSA, 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.’
All patients in the Kent outbreak have required hospital admission. Nine were admitted to the intensive care unit, where four remain.
The two students who have died are 18-year-old Juliette Kenny, who was described by her family as ‘fit, healthy and strong’ before her death, and a University of Kent student.
