EARLY IMPACT OF INTRODUCING A TEN-VALENT PNEUMOCOCCAL CONJUGATE VACCINE (PCV10) ON PNEUMOCOCCAL CARRIAGE IN NIGERIA
As Nigeria transitions from Gavi-support to self-financing of the pneumococcal conjugate vaccine (PCV), decisions on vaccine cost effectiveness should be based on local vaccine impact data. Herd immunity against carriage is a major contributor to PCV impact. So, carriage surveys are a useful option for impact assessments in the absence of disease surveillance systems.
We conducted nasopharyngeal carriage surveys (2017-2019) according to WHO guidelines among randomly selected residents of two locations (urban and rural) in Nigeria. PCV10 was introduced in 2016 in these locations and reached a modest coverage of 37% and 61% by 2019. Carriage prevalence ratios (PR) before and after PCV10 introduction were estimated using log-binomial regression.
There was a 38% (PR-0.62 [95%CI:0.53-0.72]) and 21% (PR-0.79 [95%CI:0.66-0.94]) reduction in carriage of vaccine serotypes respectively among vaccine-target (<5years) and non-target) (5+ years) groups, mostly due to serotypes 19F, 23F and 6B. Carriage of non-vaccine serotypes increased by 28% (PR-1.28 [95%CI:1.15-1.42]) and 31% (PR-1.31 [95%CI:1.20-1.43]) respectively in these groups; serotypes 6A, 19A, 34, 16F and 11A were prominent.
Within three years of PCV10 introduction, we found early evidence of direct and indirect PCV effects on vaccine serotype carriage as well as serotype replacement in carriage.