Funding source: Sanofi Pasteur
A comprehensive pneumococcal carriage study is important for understanding the benefits of pneumococcal conjugate vaccine (PCV) and to facilitate the licensure and introduction of newer vaccines. Colonisation by multiple serotypes, or go colonisation is an important factor to consider in such studies as it affects the progression to invasive disease, horizontal gene transfer and host to host transmission.
Recently, the World Health Organisation (WHO) pneumococcal carriage group described the following requisites for an ideal carriage study :
- direct detection of multiple serotypes, without changing the relative proportions of various strains
- quantitative measurement of pneumococcal strains
- exclusion of any false-positive reactions through rigourous validation against Quellung reactions
- capacity to detect all possible serotypes
According to the latest data available from WHO, pneumococcal conjugate vaccines had been introduced in 117 countries by the end of 2014, and the global coverage was estimated at 31%. With the introduction of PCV, serotype replacement and increase in invasive disease by non-vaccine serotypes have been reported in several countries (2-5). Therefore, in order to understand the pneumococcal carriage in the nasopharynx, particularly in the context of determining baseline carriage prior to trial of a novel pneumococcal conjugate vaccine, studies would need to be conducted in infants in populations where PCV has not been introduced or vaccine and/or serotype coverage is very low, as well as in populations with good PCV coverage.