Clinical trials on Menactra’s (MCV4 or MenACWY-D) efficacy were not a requirement when FDA licensed its use in 2005. Menactra was the first meningococcal (serogroups A, C, Y, and W-135) conjugate vaccine and received FDA approval on the basis that the vaccine was not inferior in safety or immunogenicity when compared with Menomune meningococcal polysaccharide vaccine, the only FDA approved meningococcal vaccine available at the time. Immunogenicity was based on blood antibody testing completed 28 days following vaccine administration.
In the spring of 2005, when the CDC’s Advisory Committee on Immunization Practices (ACIP) voted that all 11-12-year olds be administered the vaccine, it acknowledged that immunogenicity data was not sufficient enough to determine the vaccine’s effectiveness. Further, data was not available to determine whether the vaccine could reduce or eliminate vaccine type meningococcal bacteria from the nasopharyngeal region and prevent persons who carried the bacteria from spreading it to others.
The ACIP also recommended that Menactra be administered at the same time as the newly licensed Tdap vaccine, though no clinical trials had examined whether administering both vaccines during the same visit would be effective or safe.
When ACIP initially recommended routine vaccination of all 11-12 year olds with Menactra meningococcal conjugate vaccine in 2005, committee members estimated that a single dose of the vaccine would be effective for an average of 22 years. However, by October of 2010, five years after the initial approval vote, ACIP voted to add a booster dose of meningococcal vaccine at age 16. By this time, data on vaccine effectiveness had determined that by age 16 to 21 years, at a time when the risk of meningococcal disease was noted to be higher, more than 50 percent of 11-12-year olds would lack any protection from the vaccine and be at risk for developing meningococcal disease.
A 2017 published study on Menactra (MenACWY-D) vaccine effectiveness found that overall, a single vaccine dose was between 51 and 80 percent effective. Within one year after vaccination, the vaccine was found to be between 49 and 91 percent effective, and after 1 to 3 years, this number decreased to between 44 and 83 percent. MenACWY-D vaccine was found to be only 25 to 79 percent effective by 3 to 8 years following vaccination. Study authors concluded that a booster dose of meningococcal conjugate vaccine would likely provide more long-term vaccine acquired immunity, but also stated that the additional impact gained from the booster dose in terms of cases prevented is likely to be limited
