Predictors of seasonal influenza vaccination among older adults in Thailand

<div><p>Background</p><p>In advance of a large influenza vaccine effectiveness (VE) cohort study among older adults in Thailand, we conducted a population-based, cross-sectional survey to measure vaccine coverage and identify factors associated with influenza vaccination among older Thai adults that could bias measures of vaccine effectiveness.</p><p>Method</p><p>We selected adults ≥65 years using a two-stage, stratified, cluster sampling design. Functional status was assessed using the 10-point Vulnerable Elders Survey (VES); scores ≥3 indicated vulnerability. Questions about attitudes towards vaccination were based on the Health Belief Model. The distance between participants’ households and the nearest vaccination clinic was calculated. Vaccination status was determined using national influenza vaccination registry. Prevalence ratios (PR) and 95% confidence intervals (CIs) were calculated using log-binomial multivariable models accounting for the sampling design.</p><p>Result</p><p>We enrolled 581 participants, of whom 60% were female, median age was 72 years, 41% had at least one chronic underlying illness, 24% met the criteria for vulnerable, and 23% did not leave the house on a daily basis. Influenza vaccination rate was 34%. In multivariable models, no variable related to functional status was associated with vaccination. The strongest predictors of vaccination were distance to the nearest vaccination center (PR 3.0, 95% CI 1.7–5.1 for participants in the closest quartile compared to the furthest), and high levels of a perception of benefits of influenza vaccination (PR 2.8, 95% CI 1.4–5.6) and cues to action (PR 2.7, 95% CI 1.5–5.1).</p><p>Conclusion</p><p>Distance to vaccination clinics should be considered in analyses of influenza VE studies in Thailand. Strategies that emphasize benefits of vaccination and encourage physicians to recommend annual influenza vaccination could improve influenza vaccine uptake among older Thai adults. Outreach to more distant and less mobile older adults may also be required to improve influenza vaccination coverage.</p></div

Data Sources Used For Pandemic (H1N1) 2009 Disease Burden Estimates.

<p>HAPS: Hunter Area Pathology Service; ED: Emergency Department.</p

Descriptive characteristics of survey participants by 2014 influenza vaccination status, Thailand^*.

<p>Descriptive characteristics of survey participants by 2014 influenza vaccination status, Thailand^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188422#t001fn001" target="_blank">*</a>}.</p

Reported and Estimated Pandemic (H1N1) 2009 Disease Burden, June 1–August 30, 2009, Hunter New England, New South Wales.

<p>*Rate ranges calculated using reported number (when available) and upper bound of calculated number.</p><p>**Case fatality and case hospitalization ratio ranges calculated using reported number and calculated point estimate of deaths and hospitalizations divided by calculated point estimate of community illness.</p

Factors associated with vaccination among survey participants in 2014 (n = 581).

<p>Factors associated with vaccination among survey participants in 2014 (n = 581).</p

Forest plot of mean standardized scores* and 95% confidence intervals of the Health Belief Model constructs by vaccination status, Thailand (n = 581).

<p>*Standardized scores (Z scores) were calculated to account for the different number of items comprising each HBM constructs (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188422#pone.0188422.s001" target="_blank">S1 Table</a>), such that all constructs of HBM had a mean of 0 and standard deviation of 1.</p

Estimated Pandemic (H1N1) 2009 Disease Burden, Hunter New England, New South Wales, June 1-August 30, 2009.

<p>Estimated Pandemic (H1N1) 2009 Disease Burden, Hunter New England, New South Wales, June 1-August 30, 2009.</p

Community ILI, Hospitalizations, and Deaths Associated with Pandemic (H1N1) 2009 Virus Infection, Hunter New England, New South Wales, June 1-August 30, 2009.

<p>Community ILI, Hospitalizations, and Deaths Associated with Pandemic (H1N1) 2009 Virus Infection, Hunter New England, New South Wales, June 1-August 30, 2009.</p

Health utilization survey (HUS) data on the frequency influenza-like illness (ILI)^* in a rural community, by age, Ballabgarh, India, 2011.

<p>Health utilization survey (HUS) data on the frequency influenza-like illness (ILI)^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196495#t001fn001" target="_blank">*</a>} in a rural community, by age, Ballabgarh, India, 2011.</p

Flow-chart depicting study methods for estimation of rates of influenza-associated ILI* in 28 villages in the Ballabgarh block (Haryana, India)–January 1 to December 31, 2011.

<p>(*ILI: influenza like illness defined as cough with history/measured fever. **AMI: acute medical illness defined any illness irrespective of symptoms excluding injury and those related to obstetric or surgical problems. ***p-y: person-years).</p