Childhood pneumococcal conjugate vaccines continue to indirectly produce widespread societal protection against invasive pneumococcal disease, a review and meta-analysis showed.
In fact, the reviewed studies suggest that the use of these vaccines in children can lead to an overall 90% drop in invasive pneumococcal disease within fewer than 10 years.
Herd immunity appears to be at work, the review authors said. The effect is so powerful that the findings raise questions about “the merit of offering [the 13-valent pneumococcal vaccine] in older groups” in places that have a children’s pneumococcal conjugate vaccine (PCV) program, the investigators said.
U.S. guidelines recommend vaccinations for older people, although the recommendations are up for review in 2018.
According to the review, childhood PCVs have had a tremendous impact since a seven-valent version (PCV7) was first released in 2000. “In vaccinated young children, disease due to serotypes included in the vaccines has been reduced to negligible levels,” the authors wrote.
But unvaccinated people, especially the elderly, remain susceptible.
The review authors, led by Tinevimbo Shiri, PhD, of the University of Warwick, Coventry, England, updated a 2013 systemic review (Vaccine. 2013 Dec 17;32[1]:133-45). They focused on studies from 1994 to 2016 that examined the effects of introducing PCV in children.
A total of 242 studies were included in the meta-analysis, published in the January issue of Lancet Global Health (2017 Jan;5[1]:e51-e9), including 70 from the previous review. Of these, only 9 (4%) were performed in poor or middle-income countries, with most of the rest having been done in North America (42%) and Europe (38%).
The researchers found that “[herd] immunity effects continued to accumulate over time and reduced disease due to PCV7 serotypes, for which follow-up data have generally been available for the longest period, with a 90% average reduction after about 9 years.”
Specifically, the review estimated it would take 8.9 years for a 90% reduction in invasive pneumococcal disease for grouped serotypes in the PCV7 and 9.5 years for the extra six grouped serotypes in the 13-valent PCV. The latter vaccine was introduced in 2010.
The researchers found evidence of a similar annual reduction in disease linked to grouped serotypes in the 23-valent pneumococcal polysaccharide vaccine in adults aged 19 and up. They noted that the 11 serotypes contained in PPV23 but not in PCV13 “did not change invasive pneumococcal disease at any age.”
The investigators added: “In countries with mature pediatric PCV programmes such as Canada, Germany, the Netherlands, the U.K., and the U.S.A., invasive pneumococcal disease due to PCV7 serotypes has been nearly eliminated through indirect protection - i.e., the average incidence of PCV7-invasive pneumococcal disease after nearly a decade of PCV7 use is less than 10 per 100,000 people. In these countries, consistent decreases in vaccine-type adult community-acquired pneumonia (CAP) or meningitis, and nonbacteraemic CAP, have been observed, indicating substantial indirect protection effects against noninvasive disease from childhood vaccination.”
The review authors noted that a major “evidence gap” in the effectiveness of childhood PCV programs in low-income countries exists. “Because these countries are increasingly undertaking childhood vaccination programs, research to assess the indirect effects in these settings is particularly relevant,” they wrote.
The review’s limitations include the possibility that the results could be thrown off by variations across nations in areas like diagnostic protocols, surveillance, and outcome measures.
The authors of the review, funded by the Policy Research Program of England’s Department of Health, reported no relevant financial disclosures.