Repeated Vaccinations against Influenza over 3 Consecutive Seasons in a Pediatric Population in the United Kingdom after Implementation of a National Immunization Program

Background: The United Kingdom (UK) initiated a publicly funded national immunization program with live attenuated influenza vaccine for all 2–3-year-olds in influenza season 2013–2014 that was extended to all 2–4-year-olds in influenza season 2014–2015 and to all 2–6-year-olds in influenza season 2015–2016. This study investigated influenza vaccination rates in 2014–2015 and 2015–2016 as a function of vaccination status in 2013–2014.

Methods: Children aged 2–3 years on September 1, 2013 and still followed in the UK’s Clinical Practice Research Datalink of primary care practices on February 28, 2016 were included in this study. Children with <12 months of medical history on September 1, 2013 were excluded. Information on administration of influenza vaccine was retrieved from records between September 1 and February 28 of each season.

Results: 45,742 children aged 2–3 years on September 1, 2013 were retained in the analysis: 20,822 (46%) were vaccinated against influenza in season 2013–2014 while 24,920 were not (54%). The table below presents the vaccination rates in seasons 2014–2015 and 2015–2016 as a function of vaccination status in 2013–2014.

	Children vaccinated in 2013–2014 (n=20,822)	Children not vaccinated in 2013–2014 (n=24,920)	Total population (n=45,742)
Vaccination in 2013–2014	100% (20,822)	0% (0)	46% (20,822)
Vaccination in 2014–2015	62% (12,858)	20% (4,978)	39% (17,836)
Vaccination in 2015–2016	47% (9,847)	22% (5,444)	33% (15,291)

The vaccination rate in the total population decreased from 46% in 2013–2014 to 39% in 2014–2015 and to 33% in 2015–2016. This trend is primarily explained by a relatively low revaccination rate among children who were vaccinated in 2013–2014: 62% in 2014–2015 and 47% in 2015–2016. Among children who were not vaccinated in 2013–2014, 20% and 22% were vaccinated in 2014–2015 and 2015–2016, respectively.

Conclusion: These findings highlight the need for continuing education on the benefits of annual revaccination against influenza. More research is also needed to better understand the barriers to annual revaccination. For instance, as children age from 2 to 4 years, they may have fewer opportunities for revaccination as they may visit their doctor less frequently and do not yet attend school.

Study sponsored by AstraZeneca.