The new measles campaign

The national measles and rubella campaign that begins next month is one of the most ambitious vaccination initiatives that Britain has undertaken. The aim is to vaccinate 95% of the seven million schoolchildren aged between 5 and 16 within one month and so to prevent an epidemic of measles that would otherwise be likely to occur early next year.1,2 The novel feature of this campaign is that it is meant to prevent an epidemic: the more usual response is to wait for an outbreak to occur before doing anything. This preventive action is likely to be far more cost effective than attempts to curtail spread once the chains of transmission are established. Experience in North America has shown that, despite the adoption of prompt and aggressive measures to control outbreaks, transmission is rarely interrupted.3,4

The campaign is based on comprehensive epidemiological surveillance data including serological studies, number of cases notified and confirmed, rates of complications and deaths, and immunisation coverage.2,5,6 These data have been used in two independent mathematical models: both have predicted a high probability of a major resurgence of measles, with the greatest burden of cases in children in secondary schools and a considerable number in children in primary schools.1 The Department of Health is convinced that the cost of preventing such an epidemic through a mass campaign will be considerably less than the direct and indirect costs of the predicted epidemic. By including rubella vaccine the campaign is expected to hasten the elimination of the congenital rubella syndrome by reducing the pool of susceptibility in adolescent boys, in whom the virus continues to circulate.7

Surveillance has shown that increasing numbers of cases of measles are already occurring in schools, confirming the probability of an epidemic if action is not taken promptly.2 Late last year and early this year several health boards in the west of Scotland saw a large increase in measles - mainly in secondary schoolchildren - which resulted in 138 admissions to one infectious disease unit alone (P Christie, personal communication). If applied to England and Wales the incidence in the Scottish outbreak would give rise to the 100 000-200 000 cases predicted by the mathematical models. The five deaths among the 10 000 cases that occurred during a recent outbreak in school-children in Quebec were further evidence of the severity of measles in older age groups and confirmed the mortality predictions of the modellers.8

The resurgence of measles in Britain is largely the result of poor vaccine coverage in the past, but over a tenth of cases occur in children who have been vaccinated.2 Vaccine failure is known to sustain transmission in populations with high vaccine coverage,9 and this is the rationale for including all schoolchildren in the campaign irrespective of whether they have been vaccinated against measles previously. The next logical step will be a recommendation of a two dose schedule - a strategy being adopted by an increasing number of countries which like Britain are seeking to eliminate measles.9 Several countries that have achieved high coverage with a single dose have experienced epidemics after “honeymoon” periods of low incidence.9 Such epidemics are attributable to an accumulation of susceptible subjects, both unvaccinated children and those in whom vaccination has failed, and are triggered when their number reaches a critical threshold. There is therefore a great epidemiological advantage in introducing a second dose in the wake of a campaign to maintain the number of susceptible subjects well below this threshold.1 The simplest strategy would be to give a second dose at school entry - when boosters of the diphtheria-tetanus and oral polio vaccines are given - but whether this strategy would be successful in reaching the 7-8% of children who miss the first dose is unknown.10 Periodic mass campaigns might be a more effective way of reaching this group, but relying on them without a guarantee that resources would be available when required would be risky. Speculation on whether this approach is a serious option in Britain must await the outcome of the present campaign.

The campaign approach for delivering measles vaccine has not been tried before in an industrialised country but has been used successfully in the Caribbean and Central and South America, where measles is now at an all time low.11 In Cuba transmission of measles seems to have been interrupted after a massive campaign in 1989 that achieved over 95% coverage of children aged 1-14.11 It will be interesting to see whether the immunisation services in Britain can match this performance. Whatever the operational outcome, the comprehensive surveillance systems in place (which now include routine salivary diagnosis in all suspected cases2) will allow the epidemiological consequences of the campaign to be assessed accurately.