Seasonal influenza vaccination strategies

The immunity that is elicited by influenza vaccines is not as long-lived as the immunity following natural influenza infection and this is especially so for individuals in the risk groups. Furthermore, influenza strains evolve and may differ year by year, therefore vaccines need to be adapted accordingly. Due to these reasons, it is recommended that vaccination take place annually.

There are three possible influenza immunisation strategies but the first is the most important and widely used in Europe:

1. Protecting the vulnerable

The main strategy of immunisation programmes in Europe is to protect the more vulnerable individuals directly or indirectly. Direct protection involves immunising people who are more likely to develop severe disease if they are infected by influenza viruses (risk groups). All individuals at risk, including the elderly, should get annual vaccination.

The 2009 Council Recommendation on seasonal influenza vaccination encourages the EU Member States to adopt and implement action plans and policies aimed at reaching seasonal influenza vaccination coverage among older age groups of 75%, and if possible that target be extended to people with chronic medical conditions. Member States are also encouraged to improve vaccination coverage among healthcare workers.
ECDC has provided an overview of vaccination recommendations for 2021-22 and coverage rates for the 2018–19 to 2020–21 influenza seasons in the technical report:  Seasonal influenza vaccination recommendations and coverage rates in EU/EEA Member States 
 

2. Protecting healthy children, adolescents and adults

Healthy toddlers and younger children are prone to severe influenza disease. A number of EU/EEA countries have initiated immunisation programmes for these younger age groups.

Influenza epidemics are also an important cause of many bouts of short-lived but debilitating illnesses leading to school and work absences. Hence many people choose to get immunised and some also have their children immunised regardless of whether there is a formal recommendation or universal vaccination programme.

In addition, due to the economic impact and social disruption, employers often encourage the immunisation of their staff and make it readily available. This includes employers of healthcare staff though the prime reason for immunising healthcare workers is protecting their patients.
 

3. Reducing overall influenza transmission

While immunising members of risk groups means direct protection, there is also an indirect protection strategy of immunising those with close contact with people in the risk groups. Furthermore, children under 6 months of age that cannot be vaccinated with current vaccines may be protected by indirect protection strategies.

Influenza vaccination strategies can aim to reduce overall influenza transmission. This is an approach that is based on the observation that much of the influenza transmission takes place in children’s daycare facilities and amongst school-age children. So immunising children and adolescents in addition to the older population, may reduce overall influenza transmission and protect those in the risk groups.
 

Yearly updates of influenza vaccines

An update of seasonal influenza vaccines is needed yearly since influenza viruses constantly evolve. How effective the seasonal influenza vaccine is each season depends on the match between the selected vaccine viruses and those found circulating and will therefore vary from year to year.

In order to find the best match and increase the vaccine effectiveness, experts meet each February/March to review the precise influenza strains to include in the forthcoming season’s vaccine to be used in the northern hemisphere. This process is managed by the World Health Organization (WHO).

The WHO Global Influenza Programme influenza strain selection meeting engages specialists who review relevant virological, epidemiological, immunological and vaccine performance information in the last seasons for the northern and southern hemispheres. Based on this review, new WHO influenza vaccine strain recommendations for the updated vaccines for the forthcoming season are agreed upon.