PCV10 protection is likely to have reduced the incidence of pneumococcal disease among all ages by between 48% and 66%.
A recent study published in Nature Communications has found that carriage of vaccine-serotype pneumococci declined with greater uptake of a 10-valent pneumococcal vaccine (PCV10).
Pneumococcal conjugate vaccines (PCVs) protect against invasive pneumococcal disease, although at a population level, this protection is driven by indirect effects. The investigators noted that PCVs prevent nasopharyngeal acquisition of vaccine-serotype pneumococci, thereby reducing transmission.
In 2015, pneumococcal disease was estimated to cause 300,000 deaths globally among children aged 1 to less than 5 years. More than 50% of these deaths occurred in Africa, and Nigeria alone accounted for nearly 50,000 of these pneumococcal deaths.
Each case of pneumococcal disease is preceded by infection from a carrier, therefore vaccine impacts on carriage can help provide a minimum estimate of disease reduction in settings lacking more expensive surveillance options. To better understand this issue, researchers documented carriage prevalence and vaccine coverage in 2 settings in Nigeria following PCV10 introduction in 2016.
Between 2014 and 2016, in 3 geographically distinct phases, Nigeria introduced the PCV10 vaccine in a 3-dose schedule for infants aged 6, 10, and 14 weeks, without a catch-up campaign. However, Nigerian health officials were unable to evaluate the impact of the vaccine program on invasive disease or pneumonia due to lack of surveillance data.
In the study, investigators conducted 5 annual carriage surveys in the rural and 4 in the urban sites, and recruited 4684 and 3653 participants, respectively. In the rural and urban sites, the proportion of eligible residents who consented to participate varied from 60% to 98% and from 63% to 99%, respectively, across the sampling age groups and surveys.
Among 4684 rural participants, vaccine-serotype carriage prevalence fell from 21% to 12% as childhood vaccine coverage in those younger than 5 years of age rose from 7% to 84%. Among 2135 urban participants, carriage prevalence fell from 16% to 9% as uptake rose from 15% to 94%. Within these ranges, carriage prevalence declined with uptake and increasing PCV10 coverage reduced pneumococcal infection at all ages.
Among the age-standardized results, overall pneumococcal carriage prevalence was consistently high across all ages in surveys at the rural site. At both sites, overall pneumococcal carriage prevalence and non-vaccine serotypes carriage prevalence were higher in children younger than 5 compared to individuals ages 5 and older. Vaccine serotype carriage prevalence was also higher in children younger than 5 years in the baseline surveys at both sites.
The investigators also assessed the PCV10 vaccination status of 2165 children younger than 5 years of age in the rural site, as well as 1313 children in the urban site. The average proportion of children for whom the caregivers had retained their vaccination card was 70% in the rural site and 80% in the urban site. PCV10 coverage with 2 or more doses increased steadily from 7% in 2016 to 84% in 2020 at the rural site, and from 15% in 2017 to 94% in 2020 at the urban site.
Although carriage is only a proxy, the investigators noted that it can be used to infer the impact of PCV10 on disease rates in these settings. A reduction in carriage prevalence will produce a proportionate reduction in the number of carriers each person contacts, reducing the incidence of carriage acquisition and the incidence of all pneumococcal diseases commensurately.
Other study results have validated the concept of additional gains from indirect vaccine effects, as well. For instance, in Kilifi, Kenya, a 74% decline in vaccine serotype carriage prevalence among children younger than 5 was associated with a 92% decline in vaccine serotype invasive pneumococcal disease in this age group.
Based on their findings in Nigeria, the investigators said PCV10 protection is likely to have reduced the incidence of pneumococcal disease among all ages by between 48% and 66%, depending on the setting. Among the majority of children younger than 5 who have now received a course of PCV10, this indirect effect will have been augmented by direct effects that are likely to be very strong.
Adamu AL, Ojal J, Abubakar IA, Odeyemi KA, Bello MM, Okoromah CAN, Karia B. The impact of introduction of the 10-valent pneumococcal conjugate vaccine on pneumococcal carriage in Nigeria. Nature Communications. 14, 2666 (2023). doi:10.1038/s41467-023-38277-z