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.
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.
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.
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 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4909992/
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.
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.
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.
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.