The vaccines introduced into Belgian vaccination programmes have considerably changed the epidemiology of the infectious diseases they target, sharply reducing their incidence. Some infections have become sporadic, such as tetanus, or have been eliminated in Belgium, such as congenital rubella and poliomyelitis. Vaccination and surveillance are still necessary, however, because of the risk of importation and the severity of these diseases.
After a general decline in the number of cases of vaccine-preventable infectious diseases in 2020-2022 as a result of the covid-19 pandemic, the year 2023 shows quite different trends:
- A steady increase in the number of cases of pertussis (since August 2023) and measles (last quarter of 2023), which has continued into 2024.
- For other pathogens, such as pneumococcus and haemophilus influenzae, the number of cases was the highest seen in the last 10 years.
- For meningococcus, the number of cases rose in 2023, but has not yet reached the trends seen before covid-19. There was also a slight increase in mumps cases.
The increase in the number of measles cases was to be expected, as measles vaccination coverage is still too low. More than half the cases were unvaccinated, and one in four people had no information about their vaccination status. Belgium, like other European countries and the WHO, is committed to eliminating measles, but inadequate vaccination coverage (<95% for two doses) makes it difficult to achieve the WHO's objectives.
As far as pertussis is concerned, vaccination coverage among children is sufficiently high, but because of the weakening of immunity over time, less serious infections can occur later in life. A typical pattern can therefore be observed, with cyclical epidemics occurring every 4 to 5 years. Infants aged between 0 and 3 months are the most vulnerable to complications. These very young children can only be protected by vaccination during pregnancy. Unfortunately, vaccination coverage of pregnant women is very low in Wallonia and Brussels.
For invasive meningococcal, pneumococcal and Haemophilus influenzae infections, the coverage rates achieved are satisfactory, but the vaccines available/present in the vaccination schedule do not protect against all serogroups/serotypes. In addition, changes or replacements of circulating serotypes/serogroups occur over time.
In the case of pneumococcus, for example, there has been a clear increase in the number of serotypes not covered by the free 13-valent PCV13 vaccine. However, some of these serogroups are contained in 15- or 20-valent vaccines, which have not yet been introduced into the vaccination schedule. In the case of meningococcus, an increase in serotypes W and Y has been observed, and this will continue in 2024. The vaccine against ACWY serotypes is available free of charge for one-year-olds, but only since mid-2023. What's more, this vaccine, which has also been recommended for adolescents by the Superior Health Council since 2019, is not free for this age group, despite the fact that adolescents are the main carriers (and therefore contaminators), along with young adults. Most cases of Haemophilus influenzae are linked to non-encapsulated strains for which there is no vaccine.
These developments and this increase are not in themselves unexpected, and do not constitute a failure of the vaccination policy: the total number of cases remains well below what it was before vaccination was introduced.
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