Immunization can help protect unimmunized children, adults and the elderly through herd effects. – VoICE
Key Concept

Key Evidence: 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.

From the VoICE Editors: For more information also see Lopman 2011.

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).
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Key Evidence: 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., Yanni, E., Krumm, C., Bekkat-Berkani, R., ... & Eichner, M. 2020. Assessing direct and indirect effects of pediatric influenza vaccination in Germany by individual-based simulations. Human Vaccines & Immunotherapeutics. 16(4).
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Key Evidence: Two years after the introduction of 10-strain pneumococcal conjugate vaccine (PCV-10) in Mozambique, the percent of unvaccinated children under five years of age who carried pneumococcal strains in the vaccine declined 30% among HIV-infected children, while no significant decline in unvaccinated HIV-negative children was seen.

Sigauque B, Moiane B, Massora S et al. 2018. Early declines in vaccine type pneumococcal carriage in children less than 5 years old after introduction of 10-valent pneumococcal conjugate vaccine in Mozambique. Pediatric Infectious Disease Journal . 37(10).
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Key Evidence: 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.

From the VoICE Editors: 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.
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Key Evidence: Several countries have seen a significant decrease in the number of rotavirus-related hospital admissions in rotavirus unvaccinated children ages 2-5 years who were not age eligible to receive the vaccine post introduction. The US had a 41-92% decrease, Australia had a 30-70% decrease, Belgium had a 20-64% decrease, Austria had a 35% reduction and El Salvador had a 41-81% decrease. In addition, there was a reduction in hospitalizations due to gastroenteritis of any cause by 17-51% in the US and 40% in Australia.

From the VoICE Editors: This data is from a review article of multiple studies that evaluated the benefits of rotavirus vaccine following vaccine introduction.

Patel, M.M., Glass, R., Desai, R., et al. 2012. Fulfilling the promise of rotavirus vaccines: how far have we come since licensure?. Lancet Infectious Diseases. 12(7).
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Key Evidence: While there have been concerns that vaccinating infants against varicella (chicken pox) would shift the disease to older age groups, numerous studies in countries that have introduced the vaccine have shown a decrease in varicella incidence or in hospitalizations in older age groups of 80% or greater. Indirect protection from vaccination has been reported in individuals not eligible for live vaccines and those who may be at higher risk of complications from chicken pox, such as children <1 year of age, pregnant women and immuno-compromised individuals.

Varela FH, Pinto LA, Scotta MC 2019. Global impact of varicella vaccination programs. Human Vacines & Immunotherapeutics. 15(3).
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Key Evidence: HPV vaccine given to young women may also protect similarly-aged men against oropharyngeal cancers, which have been rising in incidence in the U.S. and Western Europe. In a small study in the UK, rates of oral HPV infections caused by HPV-16 were similar for males 12-24 years of age and vaccinated females (0% vs. 0.5%). This was considerably lower than the rates for unvaccinated females (5.6%) and men ≥25 years old (7.1%).

From the VoICE Editors: HPV-16 is the main HPV type linked to oropharyngeal cancers

Mehanna H, Bryant TS, Babrah J et al. 2018. Human Papillomavirus (HPV) vaccine effectiveness and potential herd immunity for reducing oncogenic oropharyngeal HPV-16 prevalence in the United Kingdom: a cross-sectional study. Clinical Infectious Diseases.
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Key Evidence: There is evidence that the 4-strain HPV vaccine protects people who haven’t been vaccinated from getting HPV infection. A study in the U.S. of sexually active 13-26 year old women found that, as the vaccination rate of these women climbed from 0% to 84% over an 11-year period, the rate of infection with any of the four vaccine strains fell 40% among those who had not been vaccinated.

Spinner, C., Ding, L., Bernstein, D.I. et al. 2019. Human Papillomavirus Vaccine Effectiveness and Herd Protection in Young Women. Pediatrics. 143(2).
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Key Evidence: According to some studies, hospitalizations from all causes of pneumonia declined in 18-39 year old adults in the U.S. by 26% 4 years after PCV7 vaccine was included in the infant vaccination schedule and by a further 12% with the first 2 years after PCV13 replaced PCV7. Though reductions in older age groups were not statistically significant, other U.S. studies showed significant reductions in pneumonia hospitalization rates in all adult age groups, including the elderly.

Wiese AD, Griffin MR, Grijalva CG 2019. Impact of pneumococcal conjugate vaccines on hospitalizations for pneumonia in the United States. Expert Review of Vaccines. 18(4).
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Key Evidence: In Nagoya, Japan, hospitalizations due to rotavirus (RV) decreased sharply in children 2-4 years of age once the percent of infants vaccinated against RV climbed to around 80%. Few of these older children had likely received the vaccine, suggesting that they were protected as a result of herd immunity.

Yoshikawa T, Matsuki T, Sato K et al. 2018. Impact of rotavirus vaccination on the burden of acute gastroenteritis in Nagoya city, Japan. Vaccine. 36.
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