Safety and immunogenicity of locally produced trivalent inactivated influenza vaccine (Tri Fluvac) in healthy Thai adults aged 18-64 years in Nakhon Phanom: A Phase III double blinded, three-arm, randomized, controlled trial.

BACKGROUND: Domestic influenza vaccine production facilitates a sustainable supply for mitigating seasonal influenza and improves national health security by providing infrastructure and experience for pandemic vaccine production, if needed. METHODS: A Phase III, double blind, randomized controlled trial was conducted from Sep 2019-Oct 2020 in healthy adults 18-64 years in Nakhon Phanom, Thailand. Randomization (3:3:1) compared study vaccine (Tri Fluvac), saline placebo, and an active comparator (licensed vaccine). Primary outcomes were superior efficacy compared to placebo based on RT-PCR-confirmed influenza virus infection within 12 months and non-inferiority compared to active comparator based on immunogenicity (HAI assay) at 28 days. Safety was also assessed. RESULTS: The trial enrolled 4,284 participants (Tri Fluvac = 1,836; placebo = 1,836; active comparator = 612). There were 29 RT-PCR positive influenza infections (10 Tri Fluvac, 5.5/1,000 PY; 19 placebo, 10.4/1,000PY; 0 comparator) for an absolute protective efficacy of 46.4 (95 % CI = -22.0-76.5) compared with placebo, but the power was 43.7 %. Seroconversion difference rates between Tri Fluvac and comparator at Day 28 were 1.74 (95 % CI: -2.77, 6.25), 2.22 (-2.40, 6.84), and -0.57 (-5.41, 4.27) for A(H1N1), A(H3N2), and B strains, respectively. Adverse and severe adverse events occurred in 175 (9.5 %) Tri Fluvac, 177 (10.8 %) placebo, and 66 (10.8 %) comparator arms (p-value = 0.437, Tri Fluvac vs. comparator) CONCLUSIONS: Tri Fluvac was well tolerated, and immunogenicity was non-inferior to the active comparator, meeting U.S. Food and Drug Administration (FDA) criteria for adult vaccine licensure. Few acute respiratory infections were reported during intense COVID-19 pandemic restrictions, resulting in insufficient power to evaluate clinical efficacy.

Does prior vaccination affect the immune response to seasonal influenza vaccination among older adults? Findings from a prospective cohort study in a Northeastern Province of Thailand.

BACKGROUND: We measured the immunogenicity of seasonal trivalent inactivated influenza vaccines (IIV3) among older Thai adults and the effect of one-year prior vaccination status on immune responses. METHOD: Adults aged ≥65 years (n = 370) were vaccinated with Southern Hemisphere IIV3 in 2015. Hemagglutination inhibition assays were performed using goose red blood cells on sera collected from the participants at baseline and after 1, 6, and 12 months of vaccination. Prior year vaccination (in 2014) was verified with the national health security office database. We analyzed the associations between prior vaccination and geometric mean titers (GMT) at each time point using generalized linear regression on logged transformed titers, and seroprotection and seroconversion using Log-binomial regression. RESULTS: At baseline, previously vaccinated participants (n = 203) had a significantly higher GMT and seroprotection against all three influenza strains than those previously unvaccinated (n = 167) (all p-values <0.001). Seroprotection rates were similar after one month in both groups for A(H1N1)pdm09 (adjusted risk ratio [aRR] 1.10, 95% CI 0.97-1.25), and A(H3N2) (aRR 1.08, 95% CI 0.87-1.33), but higher in previously vaccinated persons for B (aRR 1.20, 95% CI 1.08-1.32). At 12 months, 50% or more had seroprotection in previously vaccinated group with no difference between previously vaccinated or unvaccinated persons. Seroconversion was lower in the previously vaccinated group for A(H1N1)pdm09 (aRR 0.62, 95% CI 0.43-0.89), but did not differ between the two groups for A(H3N2) (aRR 0.94, 95% CI 0.69-1.28) and B (aRR 0.85, 95% CI 0.60-1.20). CONCLUSION: Influenza vaccination elicited good humoral response in older Thai adults. While seroconversion seemed attenuated in persons previously vaccinated for influenza A(H1N1)pdm09 (the only vaccine strain not to change), this was not apparent for influenza A(H3N2) and B, and prior vaccination was not associated with any inhibition in seroprotection.

Underlying cardiopulmonary conditions as a risk factor for influenza and respiratory syncytial virus infection among community-dwelling adults aged ≥ 65 years in Thailand: Findings from a two-year prospective cohort study.

BACKGROUND: Adults with cardiopulmonary conditions may be at increased risk of influenza and respiratory syncytial virus (RSV) infection, but it is not well-established and few data are available from middle-income countries. METHODS: Using data from a prospective cohort study of influenza vaccine effectiveness, we estimated and compared the incidences of influenza and RSV between community-dwelling Thai adults aged ≥ 65 years with and without cardiopulmonary conditions. During May 2015-May 2017, older adults in a rural province in Thailand were followed-up with weekly surveillance for acute respiratory illness (ARI), defined broadly as new onset or worsening of cough with or without fever, and hospitalized ARI. When ill, nasal self-swabs and/or nasopharyngeal swabs were collected for reverse-transcription polymerase chain reaction testing. We used Poisson regression to calculate incidence rate ratios (IRR), adjusting for age, sex, current smoking, number of hospital visits, weekly influenza activity, and influenza vaccination. RESULTS: Overall, 3220 adults with a median age of 71 years (IQR 68-76) were enrolled; 1324 (41.1%) were male; and 313 (9.7%) had ≥1 underlying cardiopulmonary condition, most commonly chronic obstructive pulmonary disease (131; 41.2%) or asthma (73; 23.3%). Participants with cardiopulmonary conditions had higher incidences of ARI, influenza, and RSV than those without (Adjusted IRR: 1.84, 95% CI 1.64-2.07; 1.86, 95% CI 1.07-3.26; 2.04, 95% CI 1.11-3.76, respectively). CONCLUSION: Older adults in rural Thailand with cardiopulmonary conditions have increased rates of ARI, influenza, and RSV infections. Our findings support efforts to ensure this population has access to influenza vaccines and other respiratory illness prevention measures.

Comparison of influenza antibody titers among women who were vaccinated in the 2nd and the 3rd trimesters of pregnancy.

BACKGROUND: We compared cord blood antibody titers in unvaccinated pregnant women to those vaccinated with seasonal influenza vaccine during the 2nd and the 3rd trimesters. METHODS: Pregnant women had cord blood collected at delivery for hemagglutination inhibition assay against vaccine reference viruses: A/California/07/2009 (H1N1)pdm09, A/Switzerland/9715293/2013 (H3N2), and B/Phuket/3073/2013 (Yamagata lineage). Geometric mean titer (GMT) ratios were calculated comparing vaccinated versus unvaccinated pregnant women, and women vaccinated in the 2nd and the 3rd trimesters. Proportions of women achieving defined titers were compared using the χ2 test. RESULTS: Of 307 women, 190 (62%) were unvaccinated. Fifty and 67 were vaccinated during the 2nd and the 3rd trimesters, respectively. Median enrollment age was 29 years (interquartile range 24-34). Sixteen (5%) women had pre-existing conditions, but none were immunocompromised. GMT ratios comparing vaccinated and unvaccinated women were 5.90 (95% confidence interval [CI] 5.06-6.96) for influenza A/California, 5.39 (95% CI 4.18-6.08) for influenza A/Switzerland, and 5.05 (95% CI 4.43-5.85) for influenza B/Phuket. Similarly, the GMT ratios comparing the 3rd and the 2nd trimester vaccinated women were 2.90 (95% CI 2.54-3.39), 2.82 (95% CI 2.56-3.13), and 2.83 (95% CI 2.56-3.14), respectively. The proportions of women with defined titers for the three vaccine reference viruses did not differ between 2nd and 3rd trimester vaccinated women (titers ≥40: 68-92% versus 70-93%; ≥110: 32% versus 33-63%; and ≥330: 4-10% versus 3-21%). CONCLUSIONS: Pregnant women vaccinated against influenza had more placental transfer of influenza antibodies to their infants than unvaccinated women. Placental transfer of antibodies was higher among those vaccinated in the 3rd trimester than in the 2nd trimester. There was no difference in the proportions of women achieving antibody titers corresponding to protection against influenza in children. Findings support the current World Health Organization's recommendation that pregnant women may be vaccinated in either 2nd or 3rd trimester of pregnancy.

Influenza virus seroincidence in a cohort of healthy and high-risk children enrolled in infancy, Bangkok, Thailand.

BACKGROUND: We measured seroconversion to influenza viruses and incidence of symptomatic influenza virus infection in a cohort of children in Bangkok, Thailand. METHODS: Children aged ≤6 months were followed for two years for acute respiratory illness (ARI) and had serum specimens taken at 6-month intervals and tested by hemagglutination inhibition (HI) assay. Seroconversion was defined as a >4-fold rise in the HI titers between time points with a titer of >40 in the second specimen. Respiratory swabs were tested by rRT-PCR for influenza. Data were analyzed using generalized linear models. RESULTS: Of 350 children, 266 (76%, 147 were healthy and 119 were high-risk) had ≥2 serum specimens collected before influenza vaccination. During the 2-year follow-up, 266 children contributed 370 person-years of observation, excluding post-vaccination periods. We identified 32 ARI cases with rRT-PCR-confirmed influenza virus infection (7 infections/100 person-years, 95% confidence interval [CI], 4-11). There were 126 episodes of influenza virus infection, resulting in a seroconversion rate of 35 infections/100 person-years (95% CI, 30-42). Rates in healthy and high-risk children did not differ. CONCLUSIONS: Influenza virus infection is common during the first two years of life among Thai children. A large proportion of infections may not be detected using the ARI case definition.

Predictors for influenza vaccination among Thai pregnant woman: The role of physicians in increasing vaccine uptake.

BACKGROUND: Physician recommendation and attitudes and beliefs of pregnant women toward influenza and vaccination may influence vaccine uptake during pregnancy. We examined how physician recommendation and health beliefs of pregnant women may jointly affect influenza vaccination during pregnancy. METHODS: Thai pregnant women aged ≥18 years and >13 gestational weeks attending antenatal care (ANC) clinics, and ANC physicians were recruited during May-August 2015. Women and physicians, linked using unique identifiers, provided data on demographic, health and work history, knowledge, attitudes, and beliefs toward influenza and vaccination, based on Health Belief Model constructs. Physicians also provided data on their practices in recommending influenza vaccination during pregnancy. Prevalence ratios for the association between knowledge, attitudes and beliefs of pregnant women, physician recommendation and documented receipt of vaccination within 30 days of the visit were calculated. RESULTS: Among 610 women, the median age was 27 years; 266 (44%) and 344 (56%) were in the second and third trimesters, respectively. Twenty-one (3%) had pre-existing conditions. Of 60 physicians with the median years of practice of 5; 17 (28%) reported frequently/usually/always recommending influenza vaccine to their pregnant patients, while 43 (72%) reported never/rarely/sometimes recommending the vaccine. Controlling for the pregnant women's knowledge and beliefs, pregnant women whose physician recommended influenza vaccination were 2.3 times (95% confidence interval 1.4-3.8) more likely to get vaccinated. CONCLUSIONS: In this study, physician recommendation was the only significant factor associated with influenza vaccine uptake among Thai pregnant women. Understanding physicians' motivation/barrier to recommending influenza vaccination to pregnant women may increase coverage.

Effect of acute respiratory illness on short-term frailty status of older adults in Nakhon Phanom, Thailand-June 2015 to June 2016: A prospective matched cohort study.

BACKGROUND: Frailty is associated with increased risk of mortality and decline in functional status among older adults. Older adults are at increased risk of severe disease from acute respiratory illness (ARIs), but ARI effects on frailty status among older adults are not well understood. We evaluated how ARIs affect short-term frailty status among community-dwelling adults aged ≥65 years in Nakhon Phanom, Thailand. METHODS: During May 2015 to May 2017, older adults were contacted weekly to identify ARIs as part of a community-based longitudinal cohort study. Each participant's frailty status was assessed at baseline and every 6 months using the Vulnerable Elders Survey-13 (VES-13). We selected cohort participants with an ARI and compared them with a sample of participants without an ARI matched on age, sex, influenza vaccination status, and most recent VES-13 score. For these matched cohort members, an additional VES-13 was recorded at 3-4 weeks after the ARI episode date. RESULTS: Of 3220 cohort study participants, 114 participants with an ARI and 111 comparison participants without an ARI were selected for the matched cohort; three comparison participants were matched to two ARI cases. We found no statistically significant difference between ARI and non-ARI participants in modified VES-13 score 3-4 weeks post-episode (cases = 0.90, controls = 0.63, P = 0.07). Only two ARI episodes required hospitalization. CONCLUSIONS: Primarily mild ARIs did not affect short-term frailty status among community-dwelling older adults in Thailand. As few cases of severe ARI were detected, the contribution of severe ARI to changes in frailty requires further investigation.

Effectiveness of trivalent inactivated influenza vaccine among community-dwelling older adults in Thailand: A two-year prospective cohort study.

BACKGROUND: We conducted a two-year prospective cohort study to measure the effectiveness of trivalent inactivated influenza vaccine (IIV3) to prevent laboratory-confirmed influenza among community-dwelling Thai adults aged ≥65 years during 2015-16 and 2016-17 influenza seasons. METHODS: In 2015, we enrolled a cohort of 3220 participants. Trained health volunteers collected baseline data and followed participants for two years with weekly surveillance for new or worsened cough with self-collection of nasal swabs. Vaccine effectiveness (VE) was estimated as 100% × (1- rate ratio of rRT-PCR -confirmed influenza) among vaccinated versus unvaccinated participants. Propensity score stratification was used to reduce differences between vaccinated and unvaccinated participants associated with access to and receipt of IIV3. FINDINGS: During 2015-16 and 2016-17, 1666 (52%) and 1498 (48%) participants received IIV3, respectively. The overall incidence of influenza during the two seasons was 14.3/1000 person-years among vaccinated participants and 20.2/1000 person-years among unvaccinated participants. VE was -4% (95% confidence interval [CI], -83%-40%) during 2015-16 when there was poor antigenic match between the dominant circulating A/H3N2 viruses and the vaccine strain, and 50% (95% CI, 12-71%) during 2016-17 when circulating and vaccine strains were well-matched. Of all three influenza subtypes in both years, significant protection was observed only against Influenza A/H3N2 during 2016-17 (VE, 49%; 95% CI, 3-73%). INTERPRETATION: During a season with well-matched circulating and vaccine strains, IIV3 was moderately effective against laboratory-confirmed influenza among older adults in Thailand.

Comparison of incidence and cost of influenza between healthy and high-risk children <60 months old in Thailand, 2011-2015.

INTRODUCTION: Thailand recommends influenza vaccination for children aged 6 months to <36 months, but investment in vaccine purchase is limited. To inform policy decision with respect to influenza disease burden and associated cost in young children and to support the continued inclusion of children as the recommended group for influenza vaccination, we conducted a prospective cohort study of children in Bangkok hospital to estimate and compare influenza incidence and cost between healthy and high-risk children. METHODS: Caregivers of healthy children and children with medical conditions ('high-risk') aged <36 months were called weekly for two years to identify acute respiratory illness (ARI) episodes and collect illness-associated costs. Children with ARI were tested for influenza viruses by polymerase chain reaction. Illnesses were categorized as mild or severe depending on whether children were hospitalized. Population-averaged Poisson models were used to compare influenza incidence by risk group. Quantile regression was used to examine differences in the median illness expenses. RESULTS: During August 2011-September 2015, 659 healthy and 490 high-risk children were enrolled; median age was 10 months. Incidence of mild influenza-associated ARI was higher among healthy than high-risk children (incidence rate ratio [IRR]: 1.67; 95% confidence interval [CI]: 1.13-2.48). Incidence of severe influenza-associated ARI did not differ (IRR: 0.40; 95% CI: 0.11-1.38). The median cost per mild influenza-associated ARI episode was $22 among healthy and $25 among high-risk children (3-4% of monthly household income; difference in medians: -$1; 95% CI for difference in medians: -$9 to $6). The median cost per severe influenza-associated ARI episode was $232 among healthy and $318 among high-risk children (26-40% and 36-54% of monthly household income, respectively; difference in medians: 110; 95% CI for difference in medians: -$352 to $571). CONCLUSIONS: Compared to high-risk children, healthy children had higher incidence of mild influenza-associated ARI but not severe influenza-associated ARI. Costs of severe influenza-associated ARI were substantial. These findings support the benefit of annual influenza vaccination in reducing the burden of influenza and associated cost in young children.

Tolerability of trivalent inactivated influenza vaccine among pregnant women, 2015.

BACKGROUND: Thailand recommends influenza vaccination among pregnant women. We conducted a cohort study to determine if the prevalence of adverse events following immunization (AEFIs) with influenza vaccine among Thai pregnant women was similar to that often cited among healthy adults. METHODS: Women who were ≥17 gestational weeks and ≥18 years of age were recruited. Demographic and health history data were collected using structured questionnaires. Women were provided with symptom diary, ruler to measure local reaction(s), and thermometer to measure body temperature. AEFIs were defined as any new symptom/abnormality occurring within four weeks after vaccination. The diaries were abstracted for frequency, duration, and level of discomfort/inconvenience of the AEFIs. Serious adverse events (SAEs) and the likelihood of AEFIs being associated with vaccination were determined using standard definitions. RESULTS: Among 305 women enrolled between July-November 2015, median age was 29 years. Of these, 223 (73%) were in their third trimester, 271 (89%) had completed secondary school or higher, and 20 (7%) reported ≥1 pre-existing conditions. AEFIs were reported in 134 women (44%; 95% confidence interval [CI] 38-50%). Soreness at the injection site (74, 24%; CI 19-29%), general weakness (50, 16%; CI 12-21%), muscle ache (49, 16%; CI 12-21%), and headache (45, 15%; CI 1-19%) were most common. Of those with AEFIs, 120 (89%) reported symptom/abnormality occurred on day 0 or day 1 following vaccination. Ten women (7%) reported the AEFIs affected daily activities. The AEFIs generally spontaneously resolved within 24 h of onset. There were two vaccine-unrelated SAEs. Of 294 women with complete follow-up, 279 (95%) had term deliveries, 12 (4%) had preterm deliveries, and 3 (1%) had miscarriage or stillbirth. CONCLUSION: In our cohort, AEFIs with influenza vaccine occurred with similar frequency to those reported among healthy adults in other studies, and were generally mild and self-limited. No influenza vaccine-associated SAEs were identified.

Predictors of seasonal influenza vaccination among older adults in Thailand.

BACKGROUND: 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. METHOD: 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. RESULT: 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). CONCLUSION: 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.

Cost-effectiveness of inactivated seasonal influenza vaccination in a cohort of Thai children ≤60 months of age.

BACKGROUND: Vaccination is the best measure to prevent influenza. We conducted a cost-effectiveness evaluation of trivalent inactivated seasonal influenza vaccination, compared to no vaccination, in children ≤60 months of age participating in a prospective cohort study in Bangkok, Thailand. METHODS: A static decision tree model was constructed to simulate the population of children in the cohort. Proportions of children with laboratory-confirmed influenza were derived from children followed weekly. The societal perspective and one-year analytic horizon were used for each influenza season; the model was repeated for three influenza seasons (2012-2014). Direct and indirect costs associated with influenza illness were collected and summed. Cost of the trivalent inactivated seasonal influenza vaccine (IIV3) including promotion, administration, and supervision cost was added for children who were vaccinated. Quality-adjusted life years (QALY), derived from literature, were used to quantify health outcomes. The incremental cost-effectiveness ratio (ICER) was calculated as the difference in the expected total costs between the vaccinated and unvaccinated groups divided by the difference in QALYs for both groups. RESULTS: Compared to no vaccination, IIV3 vaccination among children ≤60 months in our cohort was not cost-effective in the introductory year (2012 season; 24,450 USD/QALY gained), highly cost-effective in the 2013 season (554 USD/QALY gained), and cost-effective in the 2014 season (16,200 USD/QALY gained). CONCLUSION: The cost-effectiveness of IIV3 vaccination among children participating in the cohort study varied by influenza season, with vaccine cost and proportion of high-risk children demonstrating the greatest influence in sensitivity analyses. Vaccinating children against influenza can be economically favorable depending on the maturity of the program, influenza vaccine performance, and target population.

The acceptability and validity of self-collected nasal swabs for detection of influenza virus infection among older adults in Thailand.

BACKGROUND: Self-collection of nasal swabs could improve the timeliness of influenza virus detection in older adults. OBJECTIVES: Measure the acceptability, adequacy, timeliness, and validity of self-collected nasal swabs among adults >65 years in Thailand. METHODS: Our evaluation consisted of two parts: a one-month study among randomly selected, community-dwelling older adults to simulate community-based surveillance for acute respiratory infections (ARI); and a clinic study of older adults with ARI to evaluate the sensitivity and specificity of self-collected nasal swabs for influenza virus infection compared with healthcare worker (HCW)-collected nasal and nasopharyngeal swabs. RESULTS: In the community study, 24% of participants experienced an ARI during the observation period. All (100%) participants with an ARI self-collected nasal swabs within 72 hours of symptom onset of which 92% were considered adequate samples. In the clinic study, 45% of patients with ARI presented within 72 hours of symptom onset. The sensitivity of self-collected nasal swabs for detection of influenza virus infection was 78% (95% CI 40-97) compared to nasopharyngeal and 88% (95% CI 47-100) compared to nasal swabs collected by HCWs. Specificity was 100% (95% CI 97-100) compared to both methods. Self-collection of nasal swabs was found acceptable by 99% of participants in both studies. CONCLUSIONS: Self-collection of nasal swabs was acceptable to older adults in Thailand who were able to take adequate samples. Self-collection of nasal swabs may improve the timeliness of sample collection but lower sensitivity will need to be considered.

Effectiveness of the 2013 and 2014 Southern Hemisphere Influenza Vaccines Against Laboratory-confirmed Influenza in Young Children Using a Test-negative Design, Bangkok, Thailand.

BACKGROUND: The Thai Advisory Committee on Immunization Practices recommends annual influenza vaccination for children 6 months through 2 years of age, although older children may be vaccinated on request. We evaluated the effectiveness of the 2013 and 2014 inactivated influenza vaccines to reduce medically attended, laboratory-confirmed influenza illness among Thai children aged 7-60 months. METHODS: From September 2013-May 2015, children with influenza-like illness were screened with a rapid influenza diagnostic test. Enrolled children had nasal and throat swabs tested for influenza viruses using polymerase chain reaction. Cases and controls were subjects testing positive and negative, respectively, for influenza viruses by polymerase chain reaction. Vaccination status was ascertained from vaccination cards. Vaccine effectiveness (VE) was calculated as 100% × (1 - odds ratio of vaccination among cases vs. controls). RESULTS: Of the 1377 children enrolled, cases (n = 490) and controls (n = 887) were similar in demographic characteristics. Cases were less likely to receive influenza vaccine than controls in 2013 (6% vs. 14%; P = 0.02), but not in 2014 (6% vs. 7%; P = 0.57). Among cases, 126 (26%) were positive for influenza A(H1N1)pdm09 virus, 239 (49%) for influenza A(H3N2) and 124 (25%) for influenza B. One specimen was positive for both influenza A(H3N2) and B viruses. VE for full vaccination against all viruses was 64% (95% confidence interval: 21% to 84%) in 2013 and 26% (95% confidence interval: -47% to 63%) in 2014. CONCLUSIONS: Influenza vaccination was low among Thai children in this study, and VE varied by year, highlighting the need for annual monitoring of VE to better understand vaccine program effectiveness.

Knowledge, attitudes and beliefs related to seasonal influenza vaccine among pregnant women in Thailand.

BACKGROUND: In 2009, Thailand recommended pregnant women be prioritized for influenza vaccination. Vaccine uptake among Thai pregnant women is lower than other high-risk groups. METHODS: During December 2012-April 2013, we conducted a cross-sectional survey of a convenience sample of Thai pregnant women aged ≥ 15 years attending antenatal clinics at public hospitals in 8 of 77 provinces. A self-administered questionnaire covered knowledge, attitudes, and beliefs related to influenza vaccination using the Health Belief Model. We examined factors associated with willingness to be vaccinated using log-binomial regression models. RESULTS: The survey was completed by 1031 (96%) of 1072 pregnant women approached. A total of 627 (61%) women had heard about influenza vaccine and were included in the analysis, of whom 262 (42%) were willing to be vaccinated, 155 (25%) had received a healthcare provider recommendation for influenza vaccination and 25 (4%) had received the influenza vaccine during the current pregnancy. In unadjusted models, high levels of perceptions of susceptibility (prevalence ratio [PR] 1.5, 95% CI 1.2-2.0), high levels of belief in the benefits of vaccination (PR 2.3, 95% CI 1.7-3.1), moderate (PR 1.7, 95% CI 1.2-2.3) and high (PR 3.4, 95% CI 2.6-4.5) levels of encouragement by others to be vaccinated (i.e., cues to action) were positively associated with willingness to be vaccinated. Moderate (PR 0.5, 95% CI 0.4-0.7) and high levels of (PR 0.5, 95% CI 0.4-0.8) perceived barriers were negatively associated with willingness to be vaccinated. In the final adjusted model, only moderate (PR 1.5, 95% CI 1.1-2.0) and high levels of cues to action (PR 2.7, 95% CI 2.0-3.6) were statistically associated with willingness to be vaccinated. CONCLUSION: Cues to action were associated with willingness to be vaccinated and can be used to inform communication strategies during the vaccine campaign to increase influenza vaccination among Thai pregnant women.

Streptococcus suis infection in hospitalized patients, Nakhon Phanom Province, Thailand.

In Nakhon Phanom, Thailand, we identified 38 hospitalized patients with Streptococcus suis infection during 2006-2012. Deafness developed in 12 patients; none died. Thirty-five reported recent exposure to pigs/pork. Annual incidence was 0.1-2.2 cases/100,000 population (0.2-3.2 in persons ≥20 years of age). Clinicians should consider S. suis infection in areas where pig exposure is common.

Seasonal influenza vaccine coverage among high-risk populations in Thailand, 2010-2012.

BACKGROUND: The Advisory Committee on Immunization Practice of Thailand prioritizes seasonal influenza vaccinations for populations who are at highest risk for serious complications (pregnant women, children 6 months-2 years, persons ≥65 years, persons with chronic diseases, obese persons), and healthcare personnel and poultry cullers. The Thailand government purchases seasonal influenza vaccine for these groups. We assessed vaccination coverage among high-risk groups in Thailand from 2010 to 2012. METHODS: National records on persons who received publicly purchased vaccines from 2010 to 2012 were analyzed by high-risk category. Denominator data from multiple sources were compared to calculate coverage. Vaccine coverage was defined as the proportion of individuals in each category who received the vaccine. Vaccine wastage was defined as the proportion of publicly purchased vaccines that were not used. RESULTS: From 2010 to 2012, 8.18 million influenza vaccines were publicly purchased (range, 2.37-3.29 million doses/year), and vaccine purchases increased 39% over these years. Vaccine wastage was 9.5%. Approximately 5.7 million (77%) vaccine doses were administered to persons ≥65 years and persons with chronic diseases, 1.4 million (19%) to healthcare personnel/poultry cullers, 82,570 (1.1%) to children 6 months-2 years, 78,885 (1.1%) to obese persons, 26,481 (0.4%) to mentally disabled persons, and 17,787 (0.2%) to pregnant women. Between 2010 and 2012, coverage increased among persons with chronic diseases (8.6% versus 14%; p<0.01) and persons ≥65 years (12%, versus 20%; p<0.01); however, coverage decreased for mentally disabled persons (6.1% versus 4.9%; p<0.01), children 6 months-2 years (2.3% versus 0.9%; p<0.01), pregnant women (1.1% versus 0.9%; p<0.01), and obese persons (0.2% versus 0.1%; p<0.01). CONCLUSIONS: From 2010 to 2012, the availability of publicly purchased vaccines increased. While coverage remained low for all target groups, coverage was highest among persons ≥65 years and persons with chronic diseases. Annual coverage assessments are necessary to promote higher coverage among high-risk groups in Thailand.

Incidence and epidemiology of hospitalized influenza cases in rural Thailand during the influenza A (H1N1)pdm09 pandemic, 2009-2010.

BACKGROUND: Data on the burden of the 2009 influenza pandemic in Asia are limited. Influenza A(H1N1)pdm09 was first reported in Thailand in May 2009. We assessed incidence and epidemiology of influenza-associated hospitalizations during 2009-2010. METHODS: We conducted active, population-based surveillance for hospitalized cases of acute lower respiratory infection (ALRI) in all 20 hospitals in two rural provinces. ALRI patients were sampled 1∶2 for participation in an etiology study in which nasopharyngeal swabs were collected for influenza virus testing by PCR. RESULTS: Of 7,207 patients tested, 902 (12.5%) were influenza-positive, including 190 (7.8%) of 2,436 children aged <5 years; 86% were influenza A virus (46% A(H1N1)pdm09, 30% H3N2, 6.5% H1N1, 3.5% not subtyped) and 13% were influenza B virus. Cases of influenza A(H1N1)pdm09 first peaked in August 2009 when 17% of tested patients were positive. Subsequent peaks during 2009 and 2010 represented a mix of influenza A(H1N1)pdm09, H3N2, and influenza B viruses. The estimated annual incidence of hospitalized influenza cases was 136 per 100,000, highest in ages <5 years (477 per 100,000) and >75 years (407 per 100,000). The incidence of influenza A(H1N1)pdm09 was 62 per 100,000 (214 per 100,000 in children <5 years). Eleven influenza-infected patients required mechanical ventilation, and four patients died, all adults with influenza A(H1N1)pdm09 (1) or H3N2 (3). CONCLUSIONS: Influenza-associated hospitalization rates in Thailand during 2009-10 were substantial and exceeded rates described in western countries. Influenza A(H1N1)pdm09 predominated, but H3N2 also caused notable morbidity. Expanded influenza vaccination coverage could have considerable public health impact, especially in young children.