High Vaccination Coverage among Children during Influenza A(H1N1)pdm09 as a Potential Factor of Herd Immunity

Abstract

The objective of this study was to identify factors related to the expansion of infection and prevention of influenza A(H1N1)pdm09. A retrospective non-randomized cohort study (from June 2009 to May 2010) on influenza A(H1N1)pdm09 was conducted in a sample of residents from Hiroshima Prefecture, Japan. The cumulative incidence of the influenza A(H1N1)pdm09 and the pandemic vaccine effectiveness (VE) were estimated. The response rate was 53.5% (178,669/333,892). Overall, the odds ratio of non-vaccinated group to vaccinated group for cumulative incidence of influenza A(H1N1)pdm09 was 2.18 (95% confidence interval (CI): 2.13–2.23) and the VE was 43.9% (CI: 42.8–44.9). The expansion of infection, indicating the power of transmission from infected person to susceptible person, was high in the 7–15 years age groups in each area. In conclusion, results from this survey suggested that schoolchildren-based vaccination rate participates in determining the level of herd immunity to influenza and children might be the drivers of influenza transmission. For future pandemic preparedness, vaccination of schoolchildren may help to prevent disease transmission during influenza outbreak.

The estimated age-group specific influenza vaccine coverage rates in Hong Kong and the impact of the school outreach vaccination program

“…Studies have suggested that, in non-at risk patients with medium to high efficacy vaccines, the majority of influenza strains need a vaccination rate of at least 40–50% to reach herd immunity and a vaccination rate of reaching this can have a significant impact on school attendances and hospital admissions. 6 , 24 , 25 This study suggests that this is also true in Hong Kong, because when the vaccination rate was greater than 50% there was a marked reduction in influenza-related hospital admissions in children aged 6 to 11 years old. The roll-out of influenza vaccination to other age groups is likely to be beneficial to the total population.…”

“…However, the indirect impact of the increasing pediatric vaccination rate on other age groups and the total population is beyond the scope of this project but should be considered in future research. 6 …”

“…A study conducted in Oakland has shown that school-located influenza vaccination sites have 7%-11% higher influenza vaccination coverage than the comparison sites, with the program associated with lower influenza hospitalization rates, a reduction of 36% and reduced illness-specific school absenteeism, the mean absences per 100 school days decreased from 2.84 days to 2.81 days, 5 these results were also replicated in Japan. 6 With teachers and school nurses playing an essential role in educating students and their parents about the rationale, safety, and effectiveness of vaccination, school outreach vaccination programs can not only reach broad and diverse populations, and give easier access to vaccines, but they can also engage children and parents who may have previously refused vaccination. 7 , 8 …”

Seasonal Influenza and Low Flu Vaccination Coverage as Important Factors Modifying the Costs and Availability of Hospital Services in Poland: A Retrospective Comparative Study

“…It should be emphasized that the increased hospitalization costs attributed to patients with influenza are not in any way reflected by the system of healthcare service financing by the public payer, the National Health Fund. The influenza vaccinations are not reimbursed for every Polish citizen either [ 19 ], while it is known that the vaccination of schoolchildren is crucial in preventing influenza transmission in all age groups, as it determines the level of herd immunity to influenza and eliminates children as the key drivers of influenza transmission [ 21 ].…”

Vaccinating children against influenza: overall cost-effective with potential for undesirable outcomes

“…Some European countries, including the UK and Finland [2,3], extended their influenza vaccination programs to healthy children. Targeting children is expected to reduce the spread of influenza, offering indirect protection to unvaccinated individuals and non-effectively vaccinated high-risk individuals [4].…”