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The new conjugate vaccine MCV4 promises longer duration of immunity and, perhaps, greater clinical efficacy than the polysaccharide vaccine MPSV4. Questions remain about booster doses, vaccinating young children, and safety.
This review provides a brief overview of meningococcal disease, compares the characteristics of MCV4 and MPSV4, describes the indications for using the vaccines, and discusses recently raised concerns about the safety of MCV4.
A snapshot of meningococcal disease
Since the implementation of widespread immunization against Haemophilus influenzae type b and Streptococcus pneumoniae, N meningitidis has become the leading cause of meningitis among children and young adults in this country.4 Other clinical sequelae, such as pneumonia, septicemia without meningitis, occult bacteremia, and focal infections, also can follow infection with N meningitidis.
Symptoms vary somewhat with age. Older adolescents are more likely than infants to have shock and septicemia without meningitis at presentation, and to die.8
Transmission of N meningitidis occurs by respiratory droplets or direct contact with respiratory secretions (kissing, sharing drinking glasses, mouth-to-mouth resuscitation). Although invasive meningococcal disease draws the most public attention, it is believed that asymptomatic nasopharyngeal colonization with nonencapsulated, low-pathogenicity strains is actually the most common form of infection.9-11 Colonization is thought to immunize most people; those who do not produce antibodies after colonization are likely still susceptible to future infection.12 The colonization rate, which varies greatly with age, geography, and crowding, may be more than 20% in some populations.9,13
In the US, the highest incidence of invasive meningococcal disease occurs in children younger than 1 year; a second, lower peak of illness appears in late adolescence (see Figure 1).4 Although the rate of disease is higher among the youngest children, most meningococcal illness (62%) occurs in children 11 years or older.4