One in five adolescents aged 11 years appear to have inadequate protection against meningitis C and a booster dose of vaccine may therefore be needed to sustain protection amongst teenagers, according to a study published on bmj.com today.
Adolescents always used to be considered a group at high risk of contracting meningitis C, but in 1999? the government ran a mass meningitis C immunisation campaign vaccinating everyone aged 1 years, and the number of cases dropped dramatically. Since then the vaccine has been part of the routine infant immunisation programme.
Yet studies have shown that the vaccine's effectiveness in infants drops considerably over time as the level of their antibodies fall. Research has also shown that this doesn't happen in older children (aged 9 years) who are given the vaccine.
Researchers from the University of Oxford examined whether children aged 6 years when they were vaccinated as part of the national campaign, are still sufficiently protected. These children are now entering adolescence, a more high risk age. Dr Matthew Snape and colleagues studied the antibody levels in blood samples from 999 adolescents aged 11 years who were immunised as part of the 1999? vaccination campaign.
They found that children who were aged 10 years or more when vaccinated, maintained protective levels of antibodies for longer. While the majority, aged 11 years, had sufficient levels of antibodies to remain protected, approximately 10% more of those aged 14 years had that level of protection compared to those aged 11 years. The researchers suggest that one possible cause is maturation of the immune system at around the age of ten.
A meningitis booster jab was introduced for 12 month old children in 2006, but it is currently unknown how effective this will be at providing long-term immunity. However, it is known that over the next five years, a group of children who did not receive a booster, and will therefore not have sufficient levels of antibodies to protect them, will be entering adolescence.
The researchers say that over 20%, 'a significant minority', of those aged 11 years have inadequate protection against meningitis C and a booster dose of vaccine may be needed to sustain protection against meningitis C amongst teenagers.
These findings emphasise how important age at vaccination is for protection and persistence with conjugate vaccines, say Lucieni Conterno and Paul Heath in an accompanying editorial.
The fact that children in certain age groups might lose their antibodies as they get older, highlights the importance of ongoing high quality surveillance even after the disease seems to have been controlled, they add.