Assessment of the direct effectiveness of BC meningococcal vaccine in Rio de Janeiro, Brazil: a case-control study

Abstract

Background: Meningococcal disease is still a serious public health problem in many countries. A vaccine produced by Cuba was the first product against B meningococcus available on a large scale. In an attempt to control the increasing incidence of this serogroup in greater Rio de Janeiro, Brazil, the vaccine was used in 1990 in children aged 6 months-9 years. About 1.6 million children were vaccinated.

Methods: In order to assess the direct effectiveness of the vaccine in preventing disease, we conducted a case-control study during the first year after vaccination. Using a hospital-based census, we selected all children hospitalized with meningococcal disease and sampled the control group among children hospitalized with other types of meningitis. Vaccine effectiveness was estimated from the relationship, 1-OR, where OR (odds ratio) was the exponential of the logistic regression coefficient for the association between meningococcal disease and previous vaccination.

Results: A total of 275 cases and 279 controls were selected between September 1990 and October 1991. The summary adjusted measure of protection against serogroup B was 54% (95% confidence interval [CI]: 20-74%). Estimated protection varied among different age strata and place of residence, being high among children aged > or = 4 years, 71% (95% CI: 34-87%), and among those who lived in the City of Rio de Janeiro, 74% (95% CI: 42-89%).

Conclusions: The results suggest that the vaccine produced by Cuba may offer protection against serogroup B meningococcal disease, but its effects may not be homogeneous.

PIP: Meningococcal disease is still a serious public health problem in many countries. A vaccine produced by Cuba was the first product against B meningococcus available on a large scale. In an attempt to control the increasing incidence of this serogroup in greater Rio de Janeiro, Brazil, the vaccine was used in 1990 in children 6 months-9 years old. About 1.6 million children were vaccinated. In order to assess the direct effectiveness of the vaccine in preventing disease, a case-control study was conducted during the first year after vaccination. Using a hospital-based census, all children hospitalized with meningococcal disease caused by Neisseria meningitidis were selected, and the control group came from children hospitalized with other types of meningitis at the Sao Sebastiao State Infectology Institute. Vaccine effectiveness was estimated, using ordinary logistic regression, from the relationship, 1 - OR, where OR (odds ratio) was the exponential of the logistic regression coefficient for the association between meningococcal disease and previous vaccination. A total of 275 cases and 279 controls were selected between September 1990 and October 1991. 57% of the total cases belonged to serogroup B and 7% to serogroup C. The case fatality rate was 11%. Of the 279 controls, 46% were related to viral meningitis, 34% were related to meningitis caused by bacteria other than N. meningitidis, 13% were related to postmumps meningitis, 5% to tuberculosis meningitis, and 2% to other diseases. The summary-adjusted measure of protection against serogroup B was 54% (95% confidence interval [CI]: 20-74%). The combined vaccine effectiveness for 230 cases and 232 controls amounted to 58% (95% CI: 31-74%). Estimated protection varied among different age strata and place of residence, being high among children or= 4 years old, 71% (95% CI: 34-87%), and among those who lived in the City of Rio de Janeiro, 74%, (95% CI: 42-89%). The results suggest that the vaccine produced by Cuba may offer protection against serogroup B meningococcal disease, but its effects may not be homogeneous.