A recently-published long-term study that measured the efficacy of a pneumococcal vaccine in Kenya shows how widespread vaccination can improve public health.
In 2011, Kenya introduced a new pneumococcal vaccine to its child immunization program: PCV10 (or Synflorix). Prior to the introduction of PCV10, Kenya did not require nor provide children with any sort of pneumococcal immunization. This newly added childhood vaccine protects individuals from contracting 10 major strains of S. pneumoniae.
This new study observed the population of a coastal Kenyan town called Kilifi and its surrounding communities. It compared the rates of pneumococcal disease in a time period before the vaccine’s introduction (1990-2010) to the community’s pneumococcal disease rates after the implementation of PCV10 (form 2012 to 2016).
Overall, the study found that serious pneumococcal disease cases caused by any of the 10 strains targeted by PCV10 dropped by 92% among infants under five years old. Before the introduction of PCV10, the area in and around Kilifi experienced about 25 cases of pneumococcal disease (caused by PCV10 strains) annually. Cases of pneumococcal disease caused by strains not covered by PCV10 did not increase either.
Another interesting finding from the study has to do with a phenomenon called “herd immunity.” Her immunity is a positive spill-over effect that occurs when a large percentage of a community’s population is vaccinated against a particular disease. When there are very high rates of immunization, those who are not vaccinated are less likely to contract a disease because they are less likely to catch it from someone else.
The Kilifi study found evidence of herd immunity, particularly among children and infants: babies less than two months old (who are too young to receive the PCV10 vaccine) were 173% less likely to contract a pneumococcal disease despite not yet having the vaccination.
Overall, the Kilifi study comparing the pneumococcal disease rates before and after the introduction of PCV10 found that the implementation of the vaccine in the country’s childhood immunity program – and, more broadly, the widespread distribution of PCV10 – had a positive effect on the community’s public health outcomes.