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MenC vaccine demonstrates significant, long-lasting herd immunity
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The meningococcal serogroup C conjugate vaccine provided herd immunity for unvaccinated individuals that lasted at least 10 years, according to researchers at the University of Amsterdam.
In addition, they found that herd immunity was responsible for at least 36% of the overall reduction in meningococcal serogroup C (MenC) disease during the 10-year period after the vaccine’s implementation.
“Our findings provide further evidence for the conclusion that herd protection is an important part of [MenC] vaccine effectiveness,” the researchers wrote in Clinical Infectious Diseases. “It is likely that herd protection was responsible for more than the 36% decrease as reduced transmission will also have prevented serogroup C cases in the vaccinated age groups.”
The researchers compared the rate of MenC invasive disease from before the vaccine was introduced (1998-2002) to the rate after the vaccine was introduced (2002-2012), in all age groups, regardless of eligibility for the vaccine. During the study period, there were 814 cases of disease that were included in the analysis.
The incidence rate per 12 months in 1998 was 0.48 per 100,000 persons, which increased to 1.99 per 100,000 in 2001. The incidence declined after the vaccine was introduced in 2002, to 0.006 per 100,000 in 2011. The first vaccinations were in June and July 2002, in adolescents aged 15 to 18 years and children aged 1 to 5 years. Children aged 6 to 14 years were vaccinated in September, October and November 2002.
From June to August, the incidence rate decreased 65% in patients aged 15 to 18 years and 23% in patients aged 1 to 5 years vs. the rates from the same period in the previous year. The incidence rates also decreased in populations that had not been vaccinated: 49% in children younger than 1 year, 41% in children aged 6 to 14 years, 24% in patients aged 19 to 28 years and 50% in adults aged 29 to 99 years.
After performing multilocus sequence typing on 350 of the isolates, the researchers identified 53 different sequence types (STs). The most common clonal complexes were ST-11 (77%) and ST-8 (15%). Before vaccination, these isolates comprised 94% of MenC isolates, but only 81% after the vaccination campaign. A similar pattern was founded in unvaccinated patients.
“The magnitude of the herd effects following vaccination was largely unanticipated. Reliable estimates of the impact and duration of herd protection are important for policy deliberations about vaccine cost-effectiveness and the design of future immunization strategies,” the researchers wrote.
Disclosure: The researchers report no relevant financial disclosures.
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