A study revealing especially low seasonal influenza vaccine effectiveness in adults 65 or older in the UK underscores the importance of antivirals in helping to combat flu.

A report in the Eurosurveillance pointed out that, in 2016 to 2017, seasonal influenza vaccine was substantially less effective in the older age group. Public Health England-led researchers described the uptake, influenza-associated mortality and adjusted vaccine effectiveness (aVE) in this age group over influenza seasons 2010/11–2016/17. 

Elderly woman receiving vaccine. Source

To do that, researchers measured vaccine uptake in 2016/17 and five previous seasons using a sentinel general practitioners cohort in England, comparing that to laboratory-confirmed influenza in primary care from 2010–2017.

Results indicated that vaccine uptake was 64% in 65–69-year-olds, 74% in 70–74-year-olds and 80% in those aged 75 and older.

At the same time, the study team found that, overall aVE was 32.5% (95% CI: 11.6 to 48.5); aVE by subtype was 60.8% (95% CI: 33.9 to 76.7) and 50.0% (95% CI: 21.6 to 68.1) against influenza A(H1N1)pdm09 and influenza B, respectively, but only 5.6% (95% CI: - 39.2 to 35.9) against A(H3N2).

Looking specifically at all laboratory-confirmed influenza, the study found that  aVE was 45.2% (95% CI: 25.1 to 60.0) in 65–74 year olds; - 26.2% (95% CI: - 149.3 to 36.0) in 75–84 year olds and - 3.2% (95% CI: - 237.8 to 68.5) in those aged 85 years and older.

Influenza-attributable mortality was highest in seasons dominated by A(H3N2), the researchers noted.

“Vaccine uptake with non-adjuvanted, normal-dose vaccines remained high, with evidence of effectiveness against influenza A(H1N1)pdm09 and B, though poor against A(H3N2), particularly in those aged 75 years and older,” study authors concluded. “Forthcoming availability of newly licensed vaccines with wider use of antivirals can potentially further improve prevention and control of influenza in this group.”

The study noted that influenza-associated mortality has typically been lower since more widespread vaccination has occurred, but excess mortality remains statistically significant in those aged 65 years and older, especially in seasons dominated by intense circulation of influenza A(H3N2).

The researchers also emphasized that, although influenza A is mainly responsible for influenza-associated mortality among the older cohort, influenza B also poses a risk. In fact, they noted, influenza B associated deaths contributed a large proportion of seasonal mortality particularly in the 2011/12 and 2014/15 seasons.

Because of the excess mortality, the researchers recommend “prompt use of influenza antivirals in vulnerable populations for treatment and prophylaxis purposes.” Use of those drugs “is also important to mitigate the impact of severe influenza; particularly during A(H3N2) dominated seasons,” they added, acknowledging that that antivirals are currently underutilized in the UK.