These vaccines were shown to decrease disease caused by NmA, Neisseria meningitidis serogroup C (NmC), Neisseria meningitidis serogroup Y (NmY), and Neisseria meningitidis serogroup W135 (NmW) [8]. In the 1970s, a serogroup A meningococcal polysaccharide vaccine tested in field studies in ...