The impact of introduction of the 10-valent pneumococcal conjugate vaccine on pneumococcal carriage in Nigeria (original) (raw)

2023, Nature Communications

Pneumococcal conjugate vaccines (PCVs) protect against invasive pneumococcal disease (IPD) among vaccinees. However, at population level, this protection is driven by indirect effects. PCVs prevent nasopharyngeal acquisition of vaccine-serotype (VT) pneumococci, reducing onward transmission. Each disease episode is preceded by infection from a carrier, so vaccine impacts on carriage provide a minimum estimate of disease reduction in settings lacking expensive IPD surveillance. We documented carriage prevalence and vaccine coverage in two settings in Nigeria annually (2016-2020) following PCV10 introduction in 2016. Among 4,684 rural participants, VT carriage prevalence fell from 21 to 12% as childhood (<5 years) vaccine coverage rose from 7 to 84%. Among 2,135 urban participants, VT carriage prevalence fell from 16 to 9% as uptake rose from 15 to 94%. Within these ranges, carriage prevalence declined with uptake. Increasing PCV10 coverage reduced pneumococcal infection at all ages, implying at least a comparable reduction in IPD. In 2015, pneumococcal disease was estimated to cause~300,000 deaths globally among children aged 1-59 months. Over 50% of these deaths occurred in Africa, and Nigeria alone accounted for nearly 50,000 of these pneumococcal deaths 1. Between 2014 and 2016, in three geographically distinct phases, Nigeria introduced the 10-valent Pneumococcal Conjugate Vaccine (PCV10) in a three-dose schedule for infants aged 6, 10 and 14 weeks, without a catch-up campaign. Although PCV is the most expensive vaccine programme in the Nigerian portfolio, the country could not evaluate the impact of the vaccine programme on invasive disease or pneumonia due to lack of surveillance data. Every episode of pneumococcal disease is preceded by infection from another infected person, normally a nasopharyngeal carrier 2. Young children are the main reservoirs for carriage and have the highest number of effective contacts 3,4. Consequently, a reduction in carriage prevalence among young children is likely to reduce onward transmission and the incidence of disease proportionately across the population. Among vaccinated children, PCVs provide direct protection against both acquiring carriage and progressing to invasive disease following carriage of vaccine-serotypes (VTs) 2. At the population level, PCVs provide indirect protection, regardless of vaccine status, by reducing everyone's exposure to new infections from VTs. This indirect effect is driven by the direct protection against carriage among vaccinees 5,6. As vaccine coverage increases, VT carriage prevalence declines linearly due to direct protection among vaccinees and nonlinearly due to indirect protection from the consequences of reduced VT transmission in the whole population 2,5. In real-world settings, the indirect effects of PCVs account for most of the vaccine programme impact 2,7. Consequently, some countries have tailored their PCV schedules to maximise indirect effects of a