A vaccine against Streptococcus pneumoniae, a leading cause of childhood illness and mortality in the developing world, has drastically reduced the incidence of severe pneumococcal disease in children in a large Kenyan community after it was introduced in 2011, according to a new study. researchers. Johns Hopkins Bloomberg School of Public Health.
The study, published online in The Lancet April 15, is the first to assess the effect of the vaccine, called PCV10, on a large scale in Africa.
The researchers examined two time periods, 1999-2010, prior to the introduction of the vaccine and 2012-2016, after their introduction, and found that the annual average incidence of severe pneumococcal disease caused by S. pneumoniae The strains that the vaccine is designed to prevent fell by 92 percent among children under five years of age.
The incidence of diseases among older and unvaccinated age groups also dropped dramatically, suggesting that the vaccine produced an additional benefit of "herd immunity". This is because children who have been vaccinated no longer transmit disease in the community.
S. pneumoniae The infection can cause many serious diseases, which are widely termed "pneumococcal disease" and include pneumonia, meningitis, ear problems and sinusitis and sepsis (blood infection). Children are especially vulnerable to pneumococcal infections and, while pneumococcal vaccination programs in richer countries have greatly reduced the burden of pneumococcal diseases, access to pneumococcal vaccines has lagged behind in lower-income countries. Still in 2015, pneumococcal disease still affects the lives of more than 300,000 children under the age of five worldwide annually.
"There is evidence of the substantial impact of pneumococcal vaccines in the US and other rich countries, and it is truly exciting to now show a powerful population-level benefit of PCV10 vaccination in Africa, where most deaths from pneumococcal disease occur," he said. study lead author Laura Hammitt, MD, associate professor of the Department of International Health at Bloomberg School and clinical epidemiologist with the International Center for Vaccine Access and the American Indian Health Center at Bloomberg School.
Kenya by 2011 did not have a pneumococcal vaccine in its national childhood immunization schedule. That year, however, with the help of a global health organization called Gavi, the Vaccine Alliance, introduced PCV10, also called Synflorix, which is designed to protect against 10 common strains of S. pneumoniae. The Kenyan program envisaged a three-dose schedule of PCV10 vaccination in infants at six, 10 and 14 weeks of age with initial catch-up vaccination in 2011 for children under one year of age. In addition, in the study community, the Kenya Ministry of Health has extended vaccination for children up to five years of age. This has helped accelerate the population-level effects of the vaccine program.
The study population included people living in Kilifi, a city off the coast of the Indian Ocean in Kenya. The research was a collaboration involving Bloomberg School, Oxford University, London School of Hygiene and Tropical Medicine, Kenya Ministry of Health, Kilifi County Hospital and Kenya Medical Research Institute (KEMRI) in Kilifi .
The researchers calculated the incidence, or annual per capita rate, of cases of severe ("invasive" pneumococcal disease involving the 10 strains of PCV10 in children less than five years of age in the hospital during the years 1999-2016. They then compared the average incidence during the pre-vaccine period from 1999-2010 to the average incidence in 2012-2016 after the vaccine was in routine use. Comparing these before and after periods, they found that the incidence of invasive pneumococcal disease in children under five years old involving the 10 pneumococcal strains decreased by 92%. The number of invasive pneumococcal disease cases involving PCV10 strains in children under five years of age fell from an average of 25 per year in the pre-vaccine era to only one per year in the vaccine era.
The study also found that pneumococcal disease caused by non-PCV10 strains did not increase to fill the gap left by the vaccine. "There are many different strains of pneumococcus, so it's important to monitor whether the strains not included in the vaccine begin to replace those that are. That could erode some of the benefit of the vaccine through the so-called replacement disease," says Hammitt. "Fortunately, we saw no evidence of significant substitution disease now six years after the introduction of PCV10 in Kenya."
For invasive pneumococcal disease involving any S. pneumoniae mean incidence decreased by 68 percent and there was also an 85 percent reduction in pneumococcal pneumonia among children younger than 5 years.
The study revealed an additional benefit of "herd immunity," in which the vaccination of children led to reductions in the disease in older, unvaccinated age groups, reducing the spread of infection in the community. The researchers found that the incidence of pneumococcal diseases involving PCV10 strains among children under two months old – those very young to be vaccinated – declined from 173 per year per 100,000 inhabitants in the pre-vaccine period to zero after the introduction of the vaccine. Similarly, the researchers observed declines in the incidence of 74% and 81%, respectively, among children aged five to 14 years and those with more than 14 years – groups that were not vaccinated.
The protection of the herd is what makes the vaccine economical in high-income countries, but has not been observed in tropical Africa until now. "The herd immunity provided by PCV10 is important not only because it improves the health of the population as a whole, but also because it makes the vaccine more economical," says Hammitt.
In addition to monitoring the invasive disease, the study team also conducted "transport research" in which they tested the pneumococcal bacteria on the nose of more than 4,000 residents in the Kilifi area. These studies have shown declines in the transport of PCV10 strains for all age groups, from the pre-vaccination period to the post-vaccination period, which aligns with the declines observed in invasive disease. However, among children, transport of vaccine S. pneumoniae remained higher than in rich countries (6 to 8 percent in Kilifi compared to less than 1 to 2 percent in the USA).
"Persistent transport of vaccine strains could lead to rebound disease if levels of vaccine coverage did not remain high," says Hammitt. The study team plans to continue surveillance to monitor any changes in transportation and disease.
"We demonstrated a strong operational impact of using PCV10 in Kenya," says Hammitt. "Policymakers face difficult decisions about how best to use limited financial resources. Data such as these provide crucial evidence to support investment in childhood pneumococcal vaccination programs to improve the health of the population."