**2.4 Vaccination and herd immunity**

After routine and catch-up vaccinations in 2005 and 2006, as well as follow-up vaccination by 2008 in Nigeria, remarkable level of protection was observed in children. This is attributed to immunological dynamics which is an after-effect of these campaigns [32]. Herd immunity varies between heterogeneous populations in developing countries. Nigeria is the most populous country in Africa with a population of over 160million. In an assessment of immune status carried out in 2014, herd immunity against measles was 66.8% in Kano State and 73.0% in Ibadan, Oyo State. These are two largely different populations in the north and southern respectively [33]. When history of measles was compared with level of immunity, a significant association was observed between those who had measles and who had protective immunity. There was strong correlation between malnutrition and immune level, a lot of malnourished children who were vaccinated were not protected [33].
