Pneumonia is the leading killer of children under five years of age worldwide, and Streptococcus pneumoniae (the pneumococcus) is the most common cause. The pneumococcus commonly colonises the nasopharynx.
As part of a broad international research program, we are investigating the impact of pneumococcal conjugate vaccine (PCV) on pneumococcal carriage and disease in Lao PDR, Mongolia and Fiji. Fiji introduced the 10-valent PCV in 2012. Annual cross-sectional nasopharyngeal carriage surveys are being conducted to evaluate the impact of PCV10 for vaccinated and unvaccinated members of the community. This is the first vaccine impact study in the Asia/Pacific.
Nasopharyngeal swabs were collected from healthy people aged 5-8 weeks, 12-23 months, 24-83 months and adult caregivers. Swabs were stored in STGG and frozen at -80°C until analysis. Pneumococci were detected by lytA qPCR and serotyping performed by DNA-based microarray.
There has been a decline in the pneumococcal carriage rate for all age groups following PCV introduction. For example, the carriage rate for the 5-8 wko infants declined from 34% to 13%, and for the 12-23 mo children the overall rate declined from 50% to 32% (both P<0.05). There has also been a decline in vaccine-type carriage (P<0.05). The rate of multiple serotype carriage has increased, possibly due to increased carriage of non-typeable pneumococci.
We observed a decline in pneumococcal carriage in all age groups, driven by decreases in vaccine-type carriage without an associated increase in carriage of non-vaccine types. There has been an increase in multiple serotype and non-typeable pneumococcal carriage. These preliminary findings are in contrast with other vaccine impact surveys, and have significant public health implications. Samples from the 2015 survey are currently being examined.