Immune response to flu shots preserved in seniors with well-controlled metabolic comorbidities

Older adults with well-controlled metabolic comorbidities exhibit immune response to influenza vaccine, as shown in the results of the DYNAMIC study. Notably, physical activity further increases immune response particularly for influenza A/H3N2.

In a cohort of 220 individuals (median age 71 years, 29.1 percent men), 169 (76.8 percent) seroconverted to at least one of the influenza vaccine strains contained in the trivalent inactivated seasonal influenza vaccine (IIV3) at day 28. Specifically, 124 (56.4 percent) participants seroconverted to influenza A/HK/H3N2, 110 (50.0 percent) to A/MI/H1N1, and 34 (15.5 percent) to influenza B. [NPJ Vaccines 2022;doi:10.1038/s41541-022-00548-z]

Haemagglutination-inhibition (HAI) titre response to each of the trivalent inactivated influenza vaccine strains was not influenced by age, diabetes mellitus, obesity, and baseline 25(OH)D levels.

For influenza A/HK/H3N2 specifically, more recent prior influenza vaccination and higher baseline HAI titres were associated with lower HAI fold rise. Conversely, physical activity with higher HAI fold rise in a dose-response manner (p_trend=0.015).

According to the investigators, age-related immune dysfunction and inflammation both contribute to suboptimal immune responses to standard-dose influenza vaccines in older adults, and these responses may even be lower in those with metabolic comorbidities.

In DYNAMIC, 196 (89.1 percent) individuals had at least one chronic condition. Specifically, 67 (30.5 percent) had diabetes mellitus and 150 (68.2 percent) had hyperlipidaemia. The median body mass index was 24.9 kg/m², with 91 individuals (41.4 percent) being overweight (23.0–27.4 kg/m²) and 62 (28.2 percent) being obese (≥27.5 kg/m²). There were 97 individuals (44.1 percent) who had received IIV3 in the 5 years before study enrolment.

“Our study found that older adults with well-controlled metabolic comorbidities do retain HAI response to influenza vaccine, and physical activity has a beneficial effect on HAI fold rise, particularly for influenza A/H3N2,” the investigators said.

The findings have important public health implications, as the tropical city-state of Singapore typically experiences year-round influenza circulation, with peaks coinciding with northern and southern hemisphere winters accounting for a disproportionate burden of morbidity, hospitalization, and deaths annually among older people, they added. [Lancet 2018;391:1285-1300; Morb Mortal Wkly Rep 2020;69:1305-1309; Emerg Infect Dis 2006;12:114-121]

“We [urge] the encouragement of influenza vaccine uptake among older adults. Ideally, a novel influenza vaccine with more durable protection is desirable, either using mRNA technology or other platforms targeting more conserved regions of the influenza virus,” according to the investigators.

They also underscored the importance of physical activity as a potential modifiable low-cost lifestyle intervention for vaccine HAI response, along with other wider health benefits.

More studies are needed to examine dynamic host factors that could optimize influenza vaccine effectiveness in older adults, the investigators said.