Measles cases have spread to at least seven London boroughs - but information on where more than 40% of these cases are happening has not been released.
Enfield in north London continues to be the worst impacted borough in the capital, with Haringey also hard hit, but it remains unclear which other boroughs are affected as the UK Health Security Agency (UKHSA) only publishes specific data on boroughs with ten or more infections.
UKHSA has confirmed on Thursday that, as of last week, Enfield had recorded nine additional infections, taking its total to 80 cases since the start of the year.
The data also show an additional two recorded infections in neighbouring Haringey. This takes the total of measles cases reported in the borough since the start of the year to 15.
Enfield and Haringey together represent 95 of the total 146 cases recorded in the capital. This, given UKHSA's own reporting practice, means the other 35% of documented infections in the capital have occurred across at least five additional boroughs.
The UKHSA admits that reported figures "are likely to underestimate" the actual number of infections, especially over the past month. This is due to lags in cases being reported.
Outside of London, Birmingham continues to be the hardest hit, with 43 cases since the start of the year.
North Central London Integrated Care Board (NCL ICB) is responsible for co-ordinating NHS services across Barnet, Enfield, Haringey, Camden and Islington.
Dr Jo Sauvage, the ICB's chief medical officer, says the measles outbreak is mainly affecting children in schools and nurseries, with the most severe cases - requiring hospital treatment - linked to unvaccinated patients.
The North London NHS boss reaffirmed the importance of vaccination, saying: "Measles resurges when vaccination rates fall, but this is something we can turn around.
"The vaccine is safe and effective, and by boosting uptake quickly we can prevent further outbreaks."
Enfield Council is providing advice for families on preventing the spread of measles via a dedicated web page at https://www.enfield.gov.uk/healthandwellbeing/infection-control-and-vaccination/measles.
Information for families in Haringey is also available here at https://haringey.gov.uk/health-wellbeing/health-services-support/vaccination/measles.
