**1. Introduction**

#### **1.1. Background**

To date, purulent bacterial meningitis (PBM) remains a global health challenge. Meningococcal meningitis occurs in small clusters throughout the World with seasonal variation, accounts for a variable proportion of epidemic bacterial meningitis, and is one of the leading causes of such meningitis globally with a burden that, in 2012 encompassed 395,230 deaths, or 0.7% of global mortality [1, 2].

Meningococcal disease or meningococcal meningitis is caused by bacterium *Neisseria meningitidis*, also called meningococcus. Meningococcal bacteria may cause infection, which occurs in different compartment of the body, called invasive meningococcal disease (IMD), including skin, gastrointestinal tract, or respiratory tract, among others. Ultimately, the bacteria may pass through the bloodstream and reach the nervous system causing meningococcal meningitis. After an incubation period of 2–10 days, clinical presentation starts with symptoms similar to influenza (flu-like), which cause nausea, vomiting, rash, increased sensitivity to light, and confusion. Symptoms of meningococcal disease appear usually as a sudden onset of fever, headache, and stiff neck. When treated, most patients with meningococcal meningitis recover completely with appropriate antibiotic therapy and rapid medical attention. Also, meningitis can cause severe brain damage and be fatal for 50% of untreated cases.

There is no animal reservoir, and *N. meningitidis* is obligate commensals of human and can colonize the nasopharyngeal mucosa without affecting the host, a phenomenon known as carriage. Such asymptomatic carriage of meningococcus is the most prevalent form of meningococcal infection. In none-epidemic settings, approximately 10–35% of healthy individuals carry *N. meningitidis* in the upper airway [3, 4]. Thus, only in very rare cases, *N. meningitidis* is the cause of invasive meningococcal disease. *N. meningitidis* is transmitted from person-toperson through respiratory droplets or throat secretions from carriers or eventually patients. The risk of transmission and spread increases in particular by close and prolonged contact (e.g., kissing, sneezing, coughing, promiscuity, and sharing food or drinking utensils) with an infected person (symptomatic or asymptomatic (i.e., carrier). Moreover, such risk increases with recent upper respiratory infection, while young children and teen-agers are at greatest risk of infection.

Several types of meningococcal vaccines are available including Meningococcal Polysaccharide vaccines as bivalent (groups A and C), trivalent (groups A, C and W), or tetravalent (groups A, C, Y and W). Tetravalent A, C, Y, and W conjugate vaccines have been licensed since 2005 for use in children and adults in Canada, the United States of America, and Europe. Since 1999, meningococcal conjugate vaccines against group C have been available and widely used. (e.g., Meningococcal conjugate vaccine; Meningococcal polysaccharide vaccine; Serogroup B Meningococcal B) and are recommended vaccines as the best that can prevent meningitis infection. As of June 2015, over 220 million persons aged 1–29-year old received meningococcal A conjugate vaccine against the most meningitis type prevalent among 15 countries of the African belt [2].
