Measles and measles immunisation in Norway: historical review and present situation
Notification of measles has been mandatory in Norway since 1975, when the Meldesystem for smittsomme sykdommer (MSIS, notification system) was implemented nationally (1). Since 1988, measles cases have been notified individually by name, based on laboratory confirmation or an epidemiological link to a laboratory confirmed case.
Measles vaccine was introduced in 1969 with a single dose at the age of 12 months. The measles, mumps, and rubella (MMR) vaccine was introduced in 1983 as a two dose programme (at 15 months and 13 years).
Between 1969 and 1983, measles vaccination coverage was 70-80%. Since the introduction of MMR in 1983, national coverage has been 90-95% for both doses. A third dose of MMR has been included in the programme for new military recruits (the vast majority of whom are male) since 1999, to prevent outbreaks in military camps.
Seroepidemiological surveys have shown that more than 97% of Norwegians born before the introduction of measles immunisation in 1969 had contracted measles. This confirms the assumption that almost all children in Norway contracted measles before the vaccine was introduced.
Before 1969, measles typically appeared in epidemics every three years. The annual number of notified cases has been dropping gradually since the mid-1970s, and since 1990, the annual figures have been below 20, except in 1990 (95 cases), 1992 (73 cases), and 1996 (23 cases). All these cases were laboratory confirmed or linked to laboratory confirmed cases.
The most recent outbreak was in Nesodden, a municipality outside Oslo, at the end of 1996. Fourteen cases were reported to MSIS, and the local health authority registered a total of 82 cases. Most of the patients had refused vaccination for reasons of personal conviction, and only three had been immunised against measles. The disease was probably brought to Nesodden by two unvaccinated children who had been exposed to measles while visiting Switzerland.
Eight cases have been reported between 1998 and 2001. Six patients contracted the disease outside Norway (in Mongolia, Pakistan, and Sri Lanka), and one was a secondary case. The other case, which had no known link with a source outside Norway, was reported in 1999.
These figures indicate that measles is no longer endemic in Norway.
Table. Number of measles cases and deaths from measles reported in 10 year periods 1931-2000. Source: MSIS and Statistics Norway
|10 year period
The numbers of reported cases and deaths in the table should be interpreted with care as substantial underreporting of cases is probable, particularly in the pre-vaccine era when practically all children contracted measles. Cases reported since 1988 are laboratory confirmed, but cases reported before 1988 were based mainly on clinical diagnoses. The numbers of deaths must be considered minimum numbers as mortality statistics are based on the primary diagnosis on the death certificate, and cases where measles were a contributing cause of death will not be included.
Cases of encephalitis due to measles have been notified individually since 1975. Up to 2002 a total of 23 cases have been reported to MSIS, the last case being in 1994.
MSIS receives between 50 and 90 notifications annually of adverse events after MMR vaccination. Of these, fewer than 10 are classified as severe adverse events (allergic reactions, febrile seizures leading to hospitalisation and thrombocytopenia). There have been no deaths related to MMR or measles immunisation in Norway.
Some local health authorities are reporting growing concern among parents about MMR and autism, and are requesting monovalent vaccines. Extensive studies have shown no link (2,3). The Nasjonalt folkehelseinstitutt (Norwegian Institute of Public Health, NIPH) recommends MMR as the safest and best-studied vaccine. As the vaccine supplier for the national immunisation programme in Norway, NIPH make efforts to provide monovalent vaccines for those who demand it. It has, however, proved difficult to get such vaccines.