In response to the increasing incidence of meningococcal
C disease in the Netherlands since 2000, routine conjugated meningococcal
C vaccination for children aged 14 months and a catch up campaign for all
1-18 year olds was implemented (coverage ±90%) in June-November 2002
(1, 2). The age groups with the highest incidence of meningococcal C disease,
those aged 1-5 and 15-18 years, were vaccinated in June-July 2002. For logistic
reasons those aged 6-14 years were vaccinated later, in Sept-Nov 2002.
Figure: Incidence (per 100 000 inhabitants) of meningococcal
disease in the Netherlands from 2000 onwards.
Data are based on Neisseria meningitidis isolates, from patients
with meningococcal disease, sent to NRBM.
Incidence of meningococcal C disease decreased soon after the vaccination
campaign was carried out. The highest incidence of serogroup C disease had
been reported in January-March 2002 (3.1, 2.8, 2.2/100 000). In the same
months in 2003 the incidence had decreased to 0.4/100 000 (figure). The
number of patients in the first three months after the campaign (November
2002-January 2003) was almost 90% lower than during the same period of the
previous year (97 versus 11). Since the introduction of meningococcal C
conjugate vaccine, no cases of meningococcal C disease have been reported
in children previously vaccinated (3).
Incidence of meningococcal disease also decreased in non-vaccinated age
groups in the first three months after the campaign. The number of patients
decreased from 48 in November 2001-January 2002 to 9 in the same period
the next year. This might be a first indication of a herd immunity effect.
(3). However, since in 2001 the number of meningococcal C cases increased
over the year and no seasonal trend was visible, re-occurence of the seasonal
influence in 2002 could have interfered with the decrease after the vaccination
campaign.
The National Institute of Public Health (RIVM) together with the Community
Health Services (CHS) and the Netherlands Reference Laboratory for Bacterial
Meningitis (NRBM) began enhanced surveillance in January 2003. This will
enable monitoring of the incidence and disease burden of meningococcal C
disease, provide estimates of vaccine efficacy, and identify vaccine failures.
CHS report their notifications in accordance with infectious disease law.
These notifications with an additional questionnaire are recorded in an
electronic database and combined with typing results from NRBM by RIVM.
This surveillance is used to monitor the remaining incidence of meningococcal
disease. An additional aim of the enhanced surveillance is to gain insight
into the role of early recognition and treatment in reducing disease severity.
Despite the successful vaccination campaign, the number of patients with
meningococcal disease has returned to the same levels as before the increase
of serogroup C. Most cases are caused by meningococci of serogroup B. Disease
rates are being monitored carefully, as the introduction of a vaccine against
this serogroup is not expected before 2008 (4, 5).
Acknowledgements
The authors thank all the MHS and the NRBM for their contributions and collaboration
on the intensified meningococcal surveillance.