Cross-sectional studies provide a ‘snapshot’ of the frequency and characteristics of a disease in a population at a particular point in time.
Studying the pattern of meningococcal carriage in Africa
One cross-sectional survey was undertaken among 2,000 subjects during the 2010 rainy season survey in each of the follwing five countries: Chad, Ghana, Ethiopia, Nigeria and Senegal. With the exception of Chad, further cross-sectional surveys will be conducted in 2011 and 2012 during the rainy and dry seasons respectively.
Studying the impact of vaccination on meningococcal carriage
Cross-sectional surveys were conducted in Mali and Niger before the start of vaccination campaigns in December 2010 aiming to compare the frequency of serogroup A meningococcal carriage before and after vaccination in the population.
Preliminary results of carriage studies indicated that there was no serogroup A meningococci carriage in a representative population sample during pre-vaccination surveys conducted in those two countries.
It is anticipated that full vaccination coverage will be achieved by the end of 2011 in Mali and Niger and it is unlikely that serogroup A carriers will be found after vaccination with MenAfriVac™, making it impossible to compare results before and after vaccination campaigns.
However, serogroup A meningococcal carriers were identified in Chad during the MenAfriCar rainy season surveys conducted in 2010.
In addition, there have been recent changes in the occurrence of meningococcal disease in the meningitis belt. The 2011 meningitis epidemic season was characterized by a predominance of meningococcal serogroup A disease mainly in Chad and Cameroon with very few cases reported in Mali or Niger.
It has been confirmed that GAVI funding has been secured to start vaccination in Chad in December 2011.
Therefore, the MenAfriCar consortium will now concentrate efforts to evaluate the impact of vaccination on meningococcal carriage in Chad, surveying 5,000 subjects before the 2011 vaccination campaign and on two further occasions, at 9 and 21 months after vaccination.
Further cross-sectional surveys will be conducted in Mali and Niger during the rainy and dry seasons to further investigate meningococcal carriage in the region.