Coverage of English children born between September 1992 and August 2002 by five years of age ranged from 89.5% to 94.7% for at least one dose of MMR and from 73.7% to 75.0% for two doses (Figure ). Coverage of MMR in London was lower than in England overall by 7% (for one dose) and 16% (for two doses) (Figure ). Coverage at five years declined over time, by 5.3% for MMR1 and 0.8% for MMR2
Reported MMR vaccination coverage at five years of age in England and London, 1992–2004. (MMR1 for children who received at least 1 dose and MMR2 for children who received two doses).
Figure displays the estimated vaccination status for each birth cohort in England. The proportion unvaccinated has risen from 5.1% in the 11 year old cohort to 10% in the 5 year cohort.
Derived vaccination status by age, 2004/5: a) England, b) London.
Table presents the estimated MMR vaccination status of children in each school age group using cleaned routine data. In all 1.9 million school children (5–17 years) and 0.3 million pre-school children are incompletely vaccinated for their age (i.e. have not received the scheduled doses). Of these, more than 800,000 children are completely unvaccinated. The number of susceptible children between 2 and 17 years was estimated to be 1.1 million in 2004/2005 (Table ). Using our highest estimate of misclassification, if 50% of children recorded as unvaccinated were actually partially vaccinated and the same proportion of partially vaccinated children actually fully vaccinated, the revised numbers would be 1.6 million incompletely vaccinated children, (of whom 0.4 million completely unvaccinated) leading to 0.7 million susceptible children.
Numbers of children (000s) by vaccination status and number of susceptibles by age group in England in 2004.
Susceptibility by birth cohort
Figure shows the susceptibility of each school year cohort in England (all districts combined) calculated from the cleaned routine data and using estimates of vaccine efficacy. The overall proportion susceptible was 27% among 2–4 year olds (born 2000–2002), 13% among children among primary school children (5–10 year olds) and 9% among secondary school children. However there was considerable variation between districts ranging from 19% – 46% and 4% – 27% in 2–4 and 5–10 year olds respectively. The majority of susceptible children are completely unvaccinated with MMR: of susceptible primary school children, 74% have received 0 doses, 23% a single dose, and 3% two doses.
Calculated proportion susceptible to measles, 2004/5 by age and vaccination status: a) England, b) London.
Calculated values of R
The number of DHAs in 28 SHAs in four different R bands are shown in Table . In 14 districts the levels of susceptibility were sufficiently high for R to exceed 1, indicating the potential for sustained measles transmission. Eleven of these 14 DHAs are located in London, with only 5 DHAs in London having R below 1. In a further seven DHAs, R was close to the threshold in the range 0.90–0.99, 10 DHAs in the range 0.80–0.89, and 68 DHAs had R values lower than 0.8.
Number of District Health Authorities (DHAs) in different R bands in 28 Strategic Health Authorities (SHAs) in 2004/05
When the data are analysed by SHA rather than DHA, only four SHAs (all in London) appear at risk of sustained measles transmission (Figure ).
R values in 28 Strategic Health Authorities in England, 2004/05.
If coverage remained stable after 2004/05, the total number of susceptible children aged 2–17 years would increase to around 1.2 million by 2007/8. After this time the entire school population would comprise cohorts not covered by the 1994 national vaccination campaign. Thus in SHAs that did not achieve higher coverage, the increase in susceptibility would further increase the value of R (Figure ).
Figure 5 (a-f). Evolution of the effective reproduction number, R, from 2004–05 to 2008–09 in the 28 Strategic Health Authorities in England for six possible scenarios for the under-estimation of vaccination coverage (the five SHAs in London are (more ...)
If the COVER data give a true indication of the vaccination coverage in London, (0% under-reporting, Figure ) then R has exceeded 1 in all five London SHAs since 2004/5, and would be as high as 1.34 in South East London. In these circumstances, it is surprising that no major epidemic of measles has already occurred, given the frequent introductions of imported cases. This therefore supports the belief that COVER data underestimates measles vaccination coverage in London, but the degree is uncertain. However, unless at least 50% of those reported as unvaccinated have received measles containing vaccine, the potential for an epidemic in one or more SHAs in London is reached by 2007/8 (Figure ).
The potential outbreak sizes are also sensitive to under-estimation of vaccination coverage. The total potential sizes for the DHAs where R exceeds 1 and are shown in Table .
The potential measles outbreak size (000s) by age group, under four scenarios of under-estimation of vaccine coverage.
Depending on the degree of under-estimation of vaccination coverage assumed, the model suggests that in 2007/8 the potential exists for a measles outbreak of up to approximately 100,000 cases. Most of these cases would be in school age children in London (Table ).