Herd protection against influenza

doi:10.1016/j.jcv.2006.08.020

Journal of Clinical Virology

Volume 37, Issue 4, December 2006, Pages 237-243

https://doi.org/10.1016/j.jcv.2006.08.020 Get rights and content

Abstract

Mortality and hospitalization rates due to influenza have risen despite increasing vaccine coverage for the most vulnerable population; however, those most vulnerable to complications and death are the least likely to respond to the vaccine. New strategies for influenza control are needed and indirect effectiveness (herd protection) has been demonstrated for several currently used vaccines – rubella, H. influenzae type b, pneumococcus varicella and hepatitis A. The Japanese schoolchildren program provided proof of concept of indirect effectiveness of influenza vaccine. The Central Texas field trial has demonstrated significant herd protection of adults utilizing the live, attenuated influenza vaccine (LAIV) to children. Immunization of <20% of children at the intervention site resulted in an 8–18% reduction of medically attended acute respiratory illness in adults compared to rates in the comparison sites. LAIV given by nasal spray is efficacious against matched and poorly matched prevalent strains, easy to administer and readily accepted by children for annual immunization. School-based clinics could provide a platform for rapid deployment of vaccine accessible to all segments of the population. This strategy could be critical for control of pandemic influenza.

Section snippets

Herd Protection

Indirect protection by vaccinating one group to reduce exposure of another is an old concept that has been explored and used for many years. Routine rubella vaccination of infants has essentially eliminated rubella infection in susceptible pregnant women in the US resulting in the virtual disappearance of the congenital rubella syndrome. The first vaccines against Hemophilus influenzae type b (Hib) disease were indicated for children 15–18 months of age. In the 3 years that Hib conjugate

Herd protection—influenza regional studies

A growing body of data supports the concept of herd protection for influenza. Monto et al. (1969) showed significant reduction in influenza-like illness (ILI) in all age groups during the first wave of the 1968 influenza pandemic by immunizing about 85% of schoolchildren with a single dose of a monovalent A(H3N2) inactivated vaccine. He compared age-specific rates of illness at the intervention site in Tecumseh, MI with those of the neighboring town of Adrian where the children were not offered

Proof of concept

The data presented above firmly establish the concept of herd protection. Proof of concept for herd protection with influenza vaccine is provided by the analysis of the Japanese school program (Reichert et al., 2001). In Japan, observations of extremely high influenza attack rates in schoolchildren during the 1957 influenza A(H2N2) pandemic resulted in a recommendation for annual influenza vaccination of schoolchildren. The program commenced in 1962 and made mandatory in 1977 when the less

Advantages of the live attenuated influenza vaccine

Development in the US of the live, attenuated influenza vaccine (LAIV) delivered by nasal spray further facilitates this approach by providing an efficacious vaccine that is easily administered by untrained personnel and is acceptable for annual administration to most children. A community trial funded by NIAID was commenced in Central Texas in 1997. Children in the intervention site (Temple-Belton) were offered LAIV and two other sites (Waco and Bryan-College Station) were chosen as comparison

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Influenza is a major cause of disease in children. School-based seasonal influenza vaccination can be a cost-effective tool to improve vaccine uptake among children, and can bring substantial health and economic benefits to the broader community. The acceptance and feasibility of school-based influenza vaccination are likely to be highly context-specific, but limited data exist from tropical settings with year-round influenza transmission. We conducted a qualitative study to assess acceptability and feasibility of a school-based seasonal influenza vaccination programme in Singapore.
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We conducted 40 interviews. Although preschool-aged children are currently the recommended age group for vaccination, stakeholders suggested introducing the programme in primary and/or secondary schools, where existing vaccination infrastructure would facilitate delivery. However, more comprehensive evidence on the local influenza burden and transmission patterns among children is required to develop an evidence-based, locally relevant rationale for a school-based vaccination programme and effectively engage policy-makers, school staff, and parents. Extensive, age-appropriate public education and awareness campaigns would increase the acceptability of the programme among stakeholders. Stakeholders indicated that an opt-out programme with free or subsidised vaccination would be the most likely to achieve high vaccine coverage and make access to vaccination more equitable.
Overall, participants were supportive of a free or subsidised school-based influenza vaccination programme in primary and/or secondary schools, although children in this age group are not currently a recommended group for vaccination. However, a better informed, evidence-based rationale to estimate the programme’s impact in Singapore is currently lacking. Extensive, age-appropriate public education and awareness campaigns will help ensure full support across key stakeholder groups.
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Paediatric vaccination against influenza can result in indirect protection, by reducing transmission to their unvaccinated contacts. We investigated whether influenza vaccination of children would protect them and their household members in a resource-limited setting.
We did a cluster-randomised, blinded, controlled study in three villages in India. Clusters were defined as households (ie, dwellings that shared a courtyard), and children aged 6 months to 10 years were eligible for vaccination as and when they became age-eligible throughout the study. Households were randomly assigned (1:1) by a computer-based system to intramuscular trivalent inactivated influenza vaccine (IIV3) or a control of inactivated poliovirus vaccine (IPV) in the beginning of the study; vaccination occurred once a year for 3 years. The primary efficacy outcome was laboratory-confirmed influenza in a vaccinated child with febrile acute respiratory illness, analysed in the modified intention-to-treat population (ie, children who received at least one dose of vaccine, were under surveillance, and had not an influenza infection within 15 days of last vaccine dose). The secondary outcome for indirect effectiveness (surveillance study) was febrile acute respiratory illness in an unvaccinated household member of a vaccine study participant. Data from each year (year 1: November, 2009, to October, 2010; year 2: October, 2010, to October, 2011; and year 3: October, 2011, to May, 2012) were analysed separately. Safety was analysed among all participants who were vaccinated with at least one dose of the vaccine. This trial is registered with ClinicalTrials.gov, number NCT00934245.
Between Nov 1, 2009, to May 1, 2012, we enrolled 3208 households, of which 1959 had vaccine-eligible children. 1010 households were assigned to IIV3 and 949 households were assigned to IPV. In 3 years, we vaccinated 4345 children (2132 with IIV3 and 2213 with IPV) from 1868 households (968 with IIV3 and 900 with IPV) with 10 813 unvaccinated household contacts. In year 1, influenza virus was detected in 151 (10%) of 1572 IIV3 recipients and 206 (13%) of 1633 of IPV recipients (total IIV3 vaccine efficacy 25·6% [95% CI 6·8–40·6]; p=0·010). In year 2, 105 (6%) of 1705 IIV3 recipients and 182 (10%) of 1814 IPV recipients had influenza (vaccine efficacy 41·0% [24·1–54·1]; p<0·0001). In year 3, 20 (1%) of 1670 IIV3 recipients and 81 (5%) of 1786 IPV recipients had influenza (vaccine efficacy 74·2% [57·8–84·3]; p<0·0001). In year 1, total vaccine efficacy against influenza A(H1N1)pdm09 was 14·5% (–20·4 to 39·3). In year 2, total vaccine efficacy against influenza A(H3N2) was 64·5% (48·5–75·5). Total vaccine efficacy against influenza B was 32·5% (11·3–48·6) in year 1, 4·9% (–38·9 to 34·9) in year 2, and 76·5% (59·4–86·4) in year 3. Indirect vaccine effectiveness was statistically significant only in year 3 (38·1% [7·4–58·6], p=0·0197) when influenza was detected in 39 (1%) of 4323 IIV3-allocated and 60 (1%) of 4121 IPV-allocated household unvaccinated individuals. In the IIV3 group, 225 (12%) of 1632 children in year 1, 375 (22%) of 1718 in year 2, and 209 (12%) of 1673 in year 3 had an adverse reaction (compared with 216 [13%] of 1730, 380 [21%] of 1825, and 235 [13%] of 1796, respectively, in the IPV group). The most common reactions in both groups were fever and tenderness at site. No vaccine-related deaths occurred in either group.
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View all citing articles on Scopus

View full text

ReviewHerd protection against influenza

Abstract

Section snippets

Herd Protection

Herd protection—influenza regional studies

Proof of concept

Advantages of the live attenuated influenza vaccine

Lancet

Clin Chest Med

Lancet

Vaccine

Vacccine

Seminars Pediatr Infect Dis

Vaccine

Vaccine

Decline of childhood Haemophilus influenzae type b (Hib) disease in the Hib vacccine era

JAMA

School-based adolescent hepatitis B immunization programs in the United States: strategies and successes

Pediatr Infect Dis J

Comparison of heterotypic protection against influenza A/Taiwan/86 (H1N1) by attenuated and inactivated vaccines to A/Chile/83-like viruses

J Infect Dis

Incidence of hepatitis A in Israel following universal immunization of toddlers

JAMA

Changes in invasive pneumococcal disease among HIV-infected adults living in the era of childhood pneumococcal immunization

Ann Intern Med

Direct and total effectiveness of the intranasal, live-attenuated, trivalent cold-adapted influenza virus vaccine against the 2000–2001 influenza A(H1N1) and B epidemic in healthy children

Arch Pediatr Adolesc Med

The effect of mass influenza immunization in children on the morbidity of the unvaccinated elderly

Epidemiol Infect

Serious morbidity and mortality associated with influenza epidemics

Epidemiol Rev

Emerging infections – pandemic influenza

Epidemiol Rev

The changing epidemiology of respiratory syncytial virus and influenza Impetus for new control measures

Pediatr Infect Dis J

Interpandemic influenza in the Houston area 1974–76

N Engl J Med

Epidemiologic observations of influenza B virus infections in Houston, Texas 1976–1977

Am J Epidemiol

Review
Herd protection against influenza