Effectiveness of the MenACWY-D Meningococcal Conjugate Vaccine

Introduction to the Vaccine

The meningococcal conjugate vaccine, introduced in 2005, is recommended for adolescents aged 11 to 12 years. A single dose is expected to offer protection through late adolescence; however, the peak incidence of meningococcal disease occurs during late adolescence, around ages 16 to 17. As vaccination efficacy diminishes over time, a second booster dose is advised at age 16 based on preliminary data.

Understanding Meningococcal Disease

Meningococcal disease is a severe bacterial infection caused by Neisseria meningitidis, with a case-fatality rate ranging from 10% to 15%. Survivors may also face long-term neurological issues, affecting about 20% of those who recover. Over the past two decades, the incidence of this disease has significantly decreased, from 1.1 cases per 100,000 people in 1996 to 0.4 cases per 100,000 in 2005. Nonetheless, there are still between 800 and 1,200 reported cases annually in the United States.

Vaccination Program and Subgroups

In 2005, a vaccination program was established to combat meningococcal disease. There are 13 subgroups of meningitis bacteria classified by their polysaccharide capsules, with the most prevalent types—A, B, C, W, and Y—being included in the MenACWY-D conjugate vaccines. Products such as Menactra by Sanofi Pasteur and Menveo by GlaxoSmithKline employ a method in which the polysaccharide is chemically bonded to a diphtheria toxoid, enhancing the immune response.

Evaluation of Vaccine Effectiveness

A case-control study assessing the effectiveness of the MenACWY-D vaccine was published in the journal Pediatrics. This study, conducted from 2006 to 2013, identified cases of meningococcal disease through national databases, collecting samples of bacteria or bacterial DNA. Given that meningococcal disease is a nationally reported condition requiring public health investigation, details of infected individuals were accessible. Close contacts of these individuals served as control subjects, with only those vaccinated with one dose of MenACWY-D being eligible for enrollment. Vaccination history for each case and control was verified through the vaccination provider.

Study Findings

Out of 320 identified cases of meningitis between 2006 and 2013, 181 (57%) participated in the study. The findings indicated that only 20% of meningococcal cases had been vaccinated, compared to 44% of control subjects who had received one dose of the MenACWY-D vaccine. This suggests that vaccinated individuals enjoyed greater protection against meningococcal infection. An analysis of various parameters, including the time elapsed since vaccination, smoking status, and individual health conditions prior to infection, led to the calculation of vaccine efficacy for each case and control.

The overall vaccine effectiveness estimate for the duration of 0 to 8 years post-vaccination was found to be 69%. Specifically, the effectiveness was 79% (ranging from 49% to 91%) at one year, 69% (ranging from 44% to 83%) at three years, and decreased to 61% (ranging from 25% to 79%) from three to eight years.

Conclusion and Policy Implications

Collectively, these results indicate that a single dose administered at ages 11 to 12 may not adequately prevent meningococcal disease during the critical risk period that begins around age 16. The preliminary data from this study influenced policy decisions, leading to the recommendation of a second booster dose at age 16.

Author Information

Written by: Bella Groisman, PhD