Increasing herd immunity with influenza revaccination

Characteristics of Repeated Influenza Vaccination Among Older U.S. Adults

INTRODUCTION

Annual influenza vaccination is associated with reduced mortality among older adults and lower overall public health burden of influenza. This study seeks to identify the characteristics associated with repeat influenza vaccination and determine whether age-group (51-59, 60-69, ≥70 years) differences exist.

METHODS

Using the nationally representative, longitudinal Health and Retirement Study waves 2004, 2008, 2012, and 2016, adults aged >50 years were followed from 2004 to 2016. In 2020, age-stratified, multinomial regression models were estimated to identify the factors associated with respondents receiving the vaccine repeatedly (every time point), occasionally (some years), or never, with censoring for death.

RESULTS

The overall proportion of adults repeatedly receiving influenza vaccine monotonically increased across age groups from 25.9% among adults aged 51-59 years to 62.4% among those aged ≥70 years. Black, non-Hispanics and smokers were less likely to repeatedly receive an influenza vaccine than white, non-Hispanics and nonsmokers (RR=0.40-0.61 and RR=0.60-0.75, respectively, p<0.05 for all). Those who had 1‒4 medical doctor visits in the past 2 years (RR=1.60-2.99) or cholesterol screening (RR=2.67-3.48) in the past 2 years were significantly more likely to repeatedly receive influenza vaccine than those who had none.

CONCLUSIONS

Although adults aged 60-69 years and ≥70 years are more likely to receive influenza vaccine repeatedly than adults aged 51-59 years, age-specific interventions for repeat influenza vaccination may not be as effective as interventions targeted to certain subgroups among adults aged ≥51 years.

Determining optimal community protection strategies for the influenza vaccine

Introduction: Seasonal influenza poses a major risk to the health of the population. Optimal strategies for influenza vaccination can help to reduce this risk. Areas covered: Systematic evaluations of the burden of influenza are first reviewed. Key meta-analysis, randomized trials, and observational studies are critically reviewed to provide the best estimates of the efficacy of influenza vaccine. The concept of herd effect is first introduced and this is followed by the rationale and the evidence to support herd effect that can be provided with strategic use of influenza vaccination in populations. Challenges including the effect of repeated influenza vaccination and vaccine hesitancy are reviewed. The citations were selected by the authors based on PubMed searches of the literature. Expert opinion: Efforts to develop new vaccines, including a universal vaccine, offer the best prospects for improved herd effect. Increasing uptake in new populations can increase likelihood of a herd effect.

Impact of Repeated Influenza Immunization on Respiratory Illness in Children With Preexisting Medical Conditions

PURPOSE

Annual influenza immunization in medical risk groups is recommended in many countries. Recent evidence suggests that repeated inactivated influenza vaccine (IIV) immunization throughout childhood may impair long-term immunity against influenza. We assessed whether prior immunization altered the effect of IIV in children with preexisting medical conditions on primary care-diagnosed respiratory illness (RI) episodes during the influenza season.

METHODS

Electronic records of IIV-immunized children who met the criteria for annual IIV immunization according to Dutch guidelines were extracted from a primary care database from 2004 to 2015. For each year, we collected information on IIV immunization status, primary care-attended RI episodes (including influenza-like illness, acute RI, and asthma exacerbation), and potential confounders. Generalized estimating equations were used to model the association between prior IIV and occurrence of at least one RI episode during the influenza season, with "current year immunized but without IIV history" as reference group.

RESULTS

A total of 4,183 children (follow-up duration: 11,493 child-years) were IIV immunized at least once. Adjusted estimates showed lower odds for RI in current year-immunized children with prior IIV compared with those without (odds ratio [OR] = 0.61; 95% CI, 0.47-0.78 for "current year immunized and one IIV in previous 2 years"; OR = 0.85; 95% CI, 0.68-1.07 for "current year immunized and ≥2 IIVs in previous 3 years, including prior year").

CONCLUSION

Repeated IIV immunization in children with preexisting medical conditions has no negative impact on, and may even increase, long-term protection against RI episodes diagnosed during the influenza season in primary care.

Effectiveness of the live attenuated and the inactivated influenza vaccine in two-year-olds - a nationwide cohort study Finland, influenza season 2015/16

Although widely recommended, influenza vaccination of children is part of the national vaccination programme only in few countries. In addition to Canada and the United States (US), in Europe Finland and the United Kingdom have introduced live attenuated influenza vaccine (LAIV) for healthy children in their programmes. On 22 June 2016, the US Advisory Committee on Immunizations Practices, voted against further use of LAIV due to no observed vaccine effectiveness (VE) over three consecutive influenza seasons (2013/14 to 2015/16). We summarise the results of a nationwide, register-based cohort study (N=55,258 of whom 8,086 received LAIV and 4,297 TIV); all outcome (laboratory-confirmed influenza), exposure (vaccination) and confounding variable data were retrieved from four computerised national health registers, which were linked via a unique personal identity code assigned to all permanent Finnish residents regardless of nationality. Our study provides evidence of moderate effectiveness against any laboratory-confirmed influenza of the quadrivalent LAIV vaccine (VE: 51%; 95% confidence interval (CI): 28–66%) as well as the inactivated trivalent vaccine (VE: 61%; 95% CI: 31–78%) among two-year-olds during the influenza season 2015/16 in Finland. Based on these data, Finland will continue using LAIV for young children in its National Immunisation Programme this coming influenza season.