* Td: Tetanus-diphtheria vaccine
** T: Tetanus vaccine
1- Immunisation schedule
All participating countries introduced diphtheria immunisation about 50 years ago.
Table 2 compares the current immunisation schedules. The first dose is usually
administered at either 2 or 3 months of age. The total number of diphtheria doses received
by a child in the first two years of life is three or four, the total number of doses
(including boosters) after two years of age and the age of the last dose varies widely
(five years to lifelong ten yearly boosters). The age at which low dose (d) replaces high
dose diphtheria vaccine (D) also varies.
Many countries have added extra doses to their immunisation schedule following the
recent diphtheria epidemic in the Newly Independent States (NIS). Responses differ and the
schedules are now more heterogeneous than during the 1980s, when five of the eight
countries gave the final booster at or before 2 years of age. All countries now have a
booster at least for children of school age and, with the exception of Germany (which has
introduced 10 yearly boosters in adults), a booster dose for travellers to risk areas.
Finland initiated a mass vaccination campaign in 1989-90 targeted at adults based on the
results of serosurveys that indicated low antibody levels in those aged over 40 years.
2 - Vaccination coverage
Only data for coverage with primary series can be compared due to variability in
From 1970 onwards, the Netherlands, Denmark, Finland, and Sweden have had high coverage
rates, ranging between 95% and 100%. In England and Wales coverage has increased from 80%
in the early 1970s to 96% in 1996. In France, coverage figures for three doses have been
available only since 1990, showing coverages over 95%. In Italy the coverage was over 98%
in the most recent cluster survey conducted in 1991 in seven regions. In Germany, no
coverage data are available.
France and the Netherlands have no official contraindications for diphtheria
vaccination and the only contraindication in the other countries is a severe reaction to a
previous dose. This seems to have had a negligible effect on vaccine coverage, affecting
less than 1% of those eligible for vaccination.
3 - Surveillance and epidemiology
In all participating countries diphtheria is a notifiable disease and laboratory
confirmation is required.
Diphtheria was virtually eliminated from the Netherlands, Denmark, Finland, and Sweden
in the early 1970s, with almost no cases notified with probably exhaustive surveillance.
During the same period, the situation in England and Wales was similar, with incidences
below 1 per 10 million inhabitants since 1975. In the 1970s, Germany and France reached a
high level of disease control with rates of less than 10 per 10 million, acknowledging the
less reliable surveillance data in Germany. Only Italy had a higher incidence, which only
fell below 10 per 10 million during the early 1980s.
Diphtheria is now well under control in all the participating countries. In Denmark,
France, and Sweden no cases have been notified since 1990. During the 1990s, a number of
sporadic cases have been reported from the other countries, mainly linked to the large
outbreak in the former Soviet Union. In Finland, all cases were linked to travel to the
NIS and no secondary transmission has occurred. In Germany at least eight of the 13 cases
diagnosed between January 1994 and June 1996 were linked to the NIS outbreak. In these two
countries, 29 of the 32 cases (91%) notified between 1993 and 1996 were adults aged over
20 years. All but one of the cases reported from England and Wales were also imported or
import related, mainly related to travel to south east Asia.
The experience gained from diphtheria vaccination shows that all countries
participating in ESEN have the infrastructure and resources to achieve high vaccine
coverage in children. This has resulted in a uniform high level of control of the disease,
even with wide variations in vaccination schedules, particularly with regard to the age at
the last dose. The most important factor for disease control appears to be coverage with
the primary series. This is illustrated by the situation in the 1970s, when those
countries with high coverage had eliminated domestic transmission, even with a schedule
including only two doses before the age of 1 year and a total of three doses, as in
Denmark until 1996.
Adult immunity may have been important in the resurgence of the disease and recent
studies have shown that up to a half of adults in some western European countries have low
levels of or undetectable diphtheria antibodies (2,3). Comparison between countries,
however, is hampered by the use of different methods and thresholds, justifying the
standardisation process undertaken under the ESEN project (4). Despite increasing contact
with epidemic countries, domestic transmission has not resumed in Western Europe even in
those countries with few doses in the immunisation schedule. Most recently reported cases
were adults linked epidemiologically with cases from epidemic/endemic countries. It may be
that high coverage rates in childhood result in a herd immunity that is sufficient to
prevent transmission (5,6). The high proportion of cases among adults in the few recently
notified sporadic cases in the countries under study probably reflect a combination of
more frequent exposures of adults to cases from epidemic/endemic countries at home or
through travel to these areas, the higher infectious dose due to close personal contact
(such as kissing), and the higher susceptibility in adults. The immunisation status of
older people should be checked and updated before they travel to areas where diphtheria is