| * 1983 : 1 dose Measles Rubella at 12 months. Surveillance
Measles is a notifiable disease in all but two countries (France and Germany). France
discontinued measles notification in 1985 and subsequently introduced a sentinel
surveillance system. All the countries except France and Italy seek laboratory
confirmation of suspected cases of measles. In Finland all suspected cases are laboratory
tested, whereas only a fraction of all suspected cases are tested in Denmark, England and
Wales, the Netherlands, and Sweden.
Vaccine coverage and epidemiology
The participating countries have been classified into three groups
according to the incidence of reported measles cases in the past five years (very high
level of control: < 1 case per 100 000, high level of control: 1-50/100 000, and low
level of control: > 50/100 000) (table 1). Over 20% of cases in all countries are aged
10 years or over.
Finland and Sweden have virtually eliminated measles. They both
introduced vaccination against measles in the 1970s and a two dose MMR strategy in 1982,
which almost immediately achieved a very high coverage.
Denmark, England and Wales, and the Netherlands have achieved a high
level of control of measles. Denmark introduced a two dose MMR vaccination schedule in
1987. Coverage has risen from 80 % in 1989 to 88 % in 1995, and the annual incidence
declined dramatically to less than 3/100 000 between 1992 and 1996.
Single dose vaccination against measles was introduced in the
Netherlands in 1976 with immediate coverage between 90% and 95 %. In 1987 measles vaccine
was replaced by two doses of MMR (at 14 months and 9 years) with the same level of
coverage, and a catch-up campaign for 4 year olds was carried out. Since 1990, the annual
incidence of confirmed cases has not exceeded 3/100 000.
The single dose measles vaccination schedule introduced in 1968 in
England and Wales was replaced by single dose MMR in 1988. Coverage remained below 80%
until 1988 with disease incidence exceeding 100/100 000. Coverage has risen to above 90%
during the 1990s and the incidence has fallen to less than 20/100 000. A second dose of
MMR for 4 year olds was introduced in 1996.
Two countries are classified as having low
levels of control: Italy and France. In Italy, single dose measles vaccine has been
available since 1979. Estimated coverage from cluster sample surveys remained below 50%
until 1994 and was 56% in 1997. The incidence varies between 40 and 140/100 000, with
regular epidemics. In France, single dose measles vaccine has been available since 1966
and MMR since 1986. Vaccination coverage has levelled off since 1991 at around 80% and the
average annual incidence remains around 100/100 000. In 1996 a second dose of MMR was
introduced for 11 to 13 year olds. The age at which the second dose is offered was reduced
to 3 to 6 years in 1997, in response to mathematical modelling of measles in France
facilitated by the ESEN project (4). A catch-up for unvaccinated boys and girls aged 11-13
was maintained.
In Germany, where measles vaccination (MMR) includes one dose at 15
months and a second at 6 years, no data on disease incidence or coverage are available.
Discussion
Although the performance of the surveillance systems varies between countries, our
classification based on the reported incidence of measles should be robust. In Finland, no
case of measles has been confirmed since 1996, although about 2000 suspected cases are
tested each year (5); in Sweden, only a few imported cases and cases among groups who
oppose vaccination still occur; the very low incidence of notified measles in countries in
the high control group, even if underreporting exists, makes it very unlikely that the
real incidence of measles in these countries could exceed 50/100 000.
A two dose strategy with coverages higher than 95% appears necessary to
reach elimination. In the Netherlands, transmission of measles seems not to have been
interrupted despite coverage of 90% to 95% with two doses for 20 years. Countries like
France, England and Wales, where vaccine coverage remained under 80% for many years with
no catch up programme, have built up large cohorts of susceptible people in older age
groups, with the result that the average age of cases has increased. This pool of
susceptibility represents a potential for large outbreaks with more severe disease, as
older cases are more likely to suffer severe illness. Serological surveillance in England
and Wales confirmed the accumulation of susceptible people and led to a catch-up campaign
being targeted at children aged 5 to 16 years in 1994. Serological and epidemiological
data collected since the campaign suggest that England and Wales is approaching the
elimination of endemic measles transmission with an incidence below 1/100 000 (6).
In France, efforts are currently underway to increase vaccination coverage at various
ages. Denmark may actually be in a ‘honeymoon period’, with a very low incidence
currently, but a history of moderate coverage and thus an increasing pool of people
without immunity to measles.
The three groups defined according to their level of measles control
differ by parameters other than coverage and incidence (table 1). The countries with poor
control of the disease are those where the private sector plays a substantial or even
major role in delivering immunisation (France, Germany, and Italy). In such countries
immediate and extensive implementation of immunisation strategies and targets may be more
difficult. The cost of vaccination for recipients in France and Italy may also be an
obstacle for vaccination. These three countries illustrate other characteristics that may
also reflect a lower level of priority given to measles control. Germany and Italy do not
measure coverage routinely and no immunisation targets are set. Measles is not notifiable
in France and Germany.
Rubella
Immunisation schedule
Most of the participating countries introduced rubella vaccine as selective
vaccination for prepubertal girls in the 1970s in order to prevent rubella infections in
pregnant women. Some countries included a programme to vaccinate older susceptible people.
Only Denmark and Germany introduced rubella vaccination later as part of routine MMR
immunisation for all children, in 1980 and 1987, respectively. In the late 1980s,
epidemiological data and results of mathematical modelling showed that the selective
strategy alone could not eliminate congenital rubella syndrome (CRS) (7), and all the
countries with selective vaccination strategies introduced MMR vaccination for young
children of both sexes. Selective vaccination ceased when the universal strategy was
implemented (the Netherlands and Sweden) or after a few years of mixed strategy (England
and Wales and Finland). Rubella vaccination therefore now shares the same schedule and
levels of coverage as measles vaccination. In Denmark, France, Germany, and Italy however,
catch-up doses are still indicated for unvaccinated or susceptible girls or women.
Surveillance and epidemiology
Methods of rubella surveillance vary widely, limiting comparisons between countries. In
England and Wales, Finland, and Sweden only laboratory confirmed cases are notifiable
whereas in Italy and the Netherlands notifications are only made on clinical grounds. In
France, and in Denmark since 1994, only infections during pregnancy and CRS are under
surveillance. Germany monitors CRS only. England and Wales monitor both all rubella cases
and infections during pregnancy.
Finland and Sweden have virtually eliminated rubella. In Denmark, England and Wales,
and the Netherlands lack of immunity in older children and young adults, especially males,
has led to persistence of infections during pregnancy despite a dramatic reduction in the
overall incidence of rubella due to high coverage in children. In France and Italy the
rubella virus is still circulating significantly. In Italy the shift of infections towards
higher age groups due to poor coverage in both childhood and teenage girls is of great
concern and may lead to an increasing number of infections during pregnancy . No data are
available from Germany, where the virus is likely to circulate widely.
Discussion
Data from Finland and Sweden show that rubella can be eliminated with very high
levels of coverage with a two dose MMR strategy. The second dose essentially acts as a
catch-up of older susceptibles, the primary failure rate for rubella vaccination being
very low. However, because of the early age of administration of the second dose, Finland
needed to undertake supplementary immunisation activities to fill the immunity gaps in
older children or young adults.
Data from Denmark and the Netherlands show that coverage below 95%, even with two doses
in childhood, is insufficient to eliminate CRS, because of immunity gaps in older
populations. It may be sufficient if catch-up activities are carried out in these older
age groups. Recent experience in England and Wales shows that circulation of rubella virus
is now mainly sustained through a gap in immunity in males too old to have been covered by
the 1994 campaign (8).
Mumps
Immunisation schedule and surveillance
Routine vaccination for mumps was introduced in all countries during the 1980s and the
vaccine is now given as part of MMR. The immunisation schedule, vaccination coverage, and
surveillance of mumps and measles are the same.
Epidemiology
Finland and Sweden have virtually eliminated mumps.
In Denmark, where mumps vaccination was introduced as MMR, a high level of mumps
control has been achieved. The annual incidence based on notification has remained under
1/100 000 since 1994. A third of the cases are over 20 years of age.
In the Netherlands, the introduction of a two dose schedule of MMR was followed
immediately by a fall in incidence to less than 1/100 000. The average proportion of
notified cases over 20 years of age has been over 27 % for the 1989-1996 period.
In England and Wales, in 1988, after MMR vaccine was introduced, the incidence
decreased from between 220/100 000 and 600/100 000 in the 1981-88 period to less than
50/100 000 in the 1991-95 period.
The countries with the highest incidence rates are Italy and France. In Italy the
annual incidence is still between 50 and 100/100 000 with less than 20 % of cases over 15
years of age. In France incidence exceeds 80/100 000 and the age distribution is stable
(8% to 10 % of cases were over 20 years of age from 1986 to 1988 and 11% to 13 % from 1993
to 1995).
No data are available for Germany.
The generalised use of MMR has made the situation for mumps control like that of
measles.
Conclusion
Vaccine effectiveness, level of immunity needed to interrupt the circulation of the
virus and probably duration of immunity, differ between the three antigens of the MMR
vaccine, But the levels of control of the three diseases achieved in individual countries
are very similar and depend mainly on the number of doses and levels of coverage. Very
high levels of coverage with two doses of MMR have resulted in Finland and Sweden reaching
the WHO/EURO targets of an incidence of less than 1/100 000 for measles and mumps. Data
from Denmark, England and Wales, and the Netherlands show that those countries should
reach these targets soon.
The success of the measles and rubella campaign carried out in England and Wales in
1994 and its impact on transmission of the diseases shows that countries with insufficient
past control over the disease can make up for it, provided that measures are taken to
prevent the accumulation of new cohorts of susceptibles. This requires a high level of
commitment from the health authorities, which has to be translated into the setting of
targets, implemention of managerial tools, and mobilisation of resources. The measles
elimination objective currently being adopted at the European level will represent a major
challenge for countries in the low level control group, especially as their immunisation
delivery services have less favourable characteristics for the rapid achievement of high
levels of coverage. If achieved, the benefit will be further enhanced by simultaneous
interruption of indigenous transmission of mumps and elimination of CRS.
Comparisons between countries are constrained by the lack of comparability of coverage
and surveillance data. Availability of standardised serological data through the ESEN
project will allow more detailed comparisons. |