Parts of west London have the highest proportions of unvaccinated young children against measles, mumps and rubella - and it's getting worse.
Only 73.8% of children in Westminster had received their first dose of the measles, mumps and rubella (MMR) vaccine by the time they turned two last year, the lowest vaccination coverage rate in England.
Other west London boroughs also had among the lowest numbers of protected children.
In Kensington & Chelsea it was 75.1%, and in Hammersmith & Fulham it was 80.8% - the second and fourth worst in the country respectively.
Children should receive the first dose of the MMR vaccine around the time of their first birthday, then another one between the age of three years four months and five.
The World Health Organisation has set a target of 95% of two-year-olds to have had the first dose of the MMR vaccine.
Three west London boroughs - Westminster, Kensington & Chelsea and Hammersmith & Fulham - were nowhere near that target last year.
Vaccination rates also plummeted, from 2013/14 and 2014/15, in parts of west London.
In Westminster, the coverage rate dropped by 5.7 percentage points, in Kensington & Chelsea by 5.3 percentage points and in Ealing by 4.4 percentage points, compared to the year before last.
The MMR vaccine was the subject of controversy after a now-discredited paper was published in 1998 claiming a link between the vaccine and autism.
The Lancet, the medical journal that published the original paper, fully retracted it in 2010.
A study published in April this year was the latest to find no link between the vaccine and the behavioural disorder.
Across England, there was a slight fall in the MMR vaccination rate among two-year-olds last year - the first time it has gone down since 2007/08, standing at 92.3% last year.
If a very high percentage of the population are vaccinated, it can create a 'herd immunity' effect. This is when so many people are immunised against a disease that it can't spread easily, which protects the few who could still catch it.
MMR vaccination rate at 24 months:
| Local authority | 2013/14 | 2014/15 | % point change |
| Westminster | 79.5 | 73.8 | -5.7 |
| Kensington & Chelsea | 80.4 | 75.1 | -5.3 |
| Hammersmith & Fulham | 82.7 | 80.8 | -1.9 |
| Hounslow | 87.8 | 84.8 | -3 |
| Ealing | 89.3 | 84.9 | -4.4 |
| Brent (registered with GP only) | 89.4 | 88.6 | -0.8 |
| Hillingdon | 90.8 | 89.1 | -1.7 |
| Harrow (registered with GP only) | 92.1 | 91.3 | -0.8 |
