The Knowledge Hub

What is the Knowledge Hub?

Explore the VoICE Knowledge Hub—a searchable database featuring the latest peer-reviewed research on immunization benefits, especially in low- and middle-income countries. Browse the Knowledge Hub using a variety of different filters to find vaccine evidence based on country, region, topic, or disease. Click on a tag to find more evidence on a specific area, such as the return on investment of vaccines or impacts of infectious disease outbreaks.


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A school-based flu vaccination program in California led to higher vaccination rates, fewer absences, and less flu transmission

A school-located influenza vaccination program implemented in 95 preschools and elementary schools in California was associated with increased influenza vaccination coverage, decreased school absences due to illness, and lower influenza transmission across the community. The 11% increase in flu vaccination in children enrolled in target schools was associated with fewer flu hospitalizations in the community, including 160 fewer influenza hospitalizations per 100,000 among people aged 65 and older.

Benjamin-Chung J, Arnold BF, Kennedy CJ et al.. 2020. Evaluation of a city-wide school-located influenza vaccination program in Oakland, California, with respect to vaccination coverage, school absences, and laboratory-confirmed influenza: A matched cohort study. PLoS Medicine. 17(8).

A study in Germany found that vaccinating children against influenza reduces infections in the general population

A modelling simulation study in Germany found that routine influenza vaccination coverage of 55% in children of 6 months to 17 years indirectly reduces influenza infections by 26% in the general population through pronounced herd effects. The study authors conclude that targeting children in influenza vaccination campaigns may not only reduce their individual disease burden, but also that of non-vaccinated individuals.

Schmidt-Ott R, Molnar D, Anastassopoulou A et al.. 2020. Assessing direct and indirect effects of pediatric influenza vaccination in Germany by individual-based simulations. Human Vaccines & Immunotherapeutics. 16(4).

Immunization with PCV reduced the risk of pneumococcal pneumonia in HIV-positive adults in Kenya

Prior to the introduction of PCV, adults with HIV in a rural area of Kenya were nearly five times more likely to have pneumococcal pneumonia than non-infected adults, and the majority of cases with bacteremia (blood infection) occurred in HIV positive individuals.

Bigogo GM, Audi A, Auko J et al.. 2019. Indirect effects of 10-Valent pneumococcal conjugate vaccine against adult pneumococcal pneumonia in rural western Kenya. Clinical Infectious Diseases. 69(12).

Catch-up vaccination can protect unvaccinated individuals, reducing disease burden across communities

A study in rural Kenya, over a 4-year period following the introduction of the 10-strain pneumococcal conjugate vaccine for infants, that included a catch-up vaccination campaign for children 12-59 months of age, suggests that the catch-up vaccination for older birth cohorts may have been a key factor in protecting unvaccinated individuals and speeding up the reduction of the disease in the community. In contrast, a study in The Gambia, where no catch-up campaign took place, found no herd effects during the first three years following the introduction of PCV-13 for infants.

The Gambia study publication referenced can be found at

Hammitt, L.L., Etyang, A.O., Morpeth, S.C. et al. 2019. Effect of 10-valent pneumococcal conjugate vaccine on invasive pneumococcal disease and nasopharyngeal carriage in Kenya. Lancet. 393.

Immunization against rotavirus reduced hospitalizations in both children and adults via herd protection

Several studies in the U.S. have shown that hospitalizations due to rotavirus fell sharply in children too old to be vaccinated as well as in adults after rotavirus vaccines were introduced, indicating herd protection. In one large study, rotavirus hospitalizations in 2008 — two years after the first vaccine was introduced — declined by 71% in 5-14 year old children and by 65% in 15-24 year olds compared to the pre-vaccine period.

Pindyck T, Tate JE, Parashar UD. 2018. A decade of experience with rotavirus vaccination in the United States – vaccine uptake, effectiveness, and impact. Expert Review of Vaccines. 17(7).

Cholera vaccination programs for children in slums also reduces incidence in adults through herd effects

According to a modeled data study on cholera transmission in Bangladesh, a cholera vaccination program for 1-14 year olds in the slums of Dhaka, Bangladesh involving periodic (every 3 years) campaigns would reduce cholera incidence in adults living in these areas by 40% due to the herd effects of oral cholera vaccines.

Khan IK, Levin A, Chai DL, et al.. 2018. The impact and cost-effectiveness of controlling cholera through the use of oral cholera vaccines in urban Bangladesh: a disease modeling and economic analysis. PLoS NTD. 12(10).

Herd effects from immunization can protect children undergoing cancer treatments from infections

Children with cancer often rely on herd immunity as protection from vaccine-preventable diseases, so vaccinating family members and health workers is critical. Herd effects may be the only source of protection against diseases for which the vaccines are not recommended for immunosuppressed children, such as measles.

Ward, E. M., Flowers, C.R., Gansler, T., et al.. 2017. The importance of immunization in cancer prevention, treatment, and survivorship. CA: A Cancer Journal for Clinicians. 67(5).

Cholera vaccination can provide indirect protection to unvaccinated individuals through herd immunity

The evidence on cholera disease dynamics suggests that significant herd protection can result from a relatively small number of immunizations, particularly in endemic areas where there is some natural immunity among the population.

Jeuland, M., Lucas, M., Clemens, J.,et al. 2009. A Cost–Benefit Analysis of Cholera Vaccination Programs in Beira, Mozambique. World Bank Economic Review. 23(2).