Determining optimal community protection strategies for the influenza vaccine

ABSTRACT

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.

KEYWORDS:

• Influenza
• vaccine
• herd effect
• herd immunity
• randomized controlled trials
• prevention of influenza
• community protection

Article Highlights

• The global burden of influenza morbidity and mortality is high, particularly in vulnerable populations such as the elderly and young children.

• Influenza vaccine efficacy varies as a result of numerous factors including priming, previous vaccination, waning, vaccine characteristics, influenza type and subtype, and appropriateness of antigenic match.

• Indirect protection, or herd immunity, is defined by its key assumptions regarding duration of maternal immunity, variation in age at vaccination, age differences in contact rates, seasonal variation in contact probabilities, geographic distribution of the population, and non-random social intermingling. Variation in these factors directly impacts herd immunity thresholds, epidemic potential, and informs public health measures including vaccination campaigns.

• Current challenges to estimating vaccine efficacy and effectiveness include the impact of repeat vaccinations, waning immunity, and vaccine hesitancy.

• Increasing vaccine efficacy, as well as coverage in the population, will contribute to improved herd effect against influenza. Key steps for decreasing the burden of influenza-associated morbidity and mortality will require targeted approaches to increasing vaccine acceptance and improving population uptake.

Declaration of interest

M Loeb has received funding from CIHR, NIH, WHO, as well as industry funding for influenza and pneumococcal vaccine research (Sanofi Pasteur, Seqirus, Pfizer) as well as honorarium for advising or speaking from these companies. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.