344. Effectiveness of the 2010 and 2011 trivalent inactivated influenza vaccines against hospitalization with influenza-associated acute lower respiratory infection among adults aged >=50 years in rural Thailand
Session: Poster Abstract Session: Influenza Vaccine in Children and Adults
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
  • 13_243395_Dawood_scientific_poster_FINAL.pdf (240.8 kB)
  • Background: In Thailand, the influenza burden in older adults is high, and influenza vaccine is recommended for persons aged >=65 years or with certain medical conditions.  We conducted a case-control analysis to estimate 2010 and 2011 trivalent inactivated influenza vaccine (IIV) effectiveness against hospitalization with influenza-associated acute lower respiratory infection (ALRI) among Thais aged >=50 years during two years when circulating influenza strains were well-matched to vaccine strains. 

    Methods: During 2010-2011, active surveillance for hospitalization with ALRI was conducted in 2 rural provinces; patients were tested for influenza viruses by real time RT-PCR. Vaccination status was obtained from vaccine registries.  Cases and controls were aged >=50 years with nasopharyngeal swabs positive and negative for influenza viruses, respectively.  Influenza vaccination was defined as receipt of IIV >=14 and <=182 days before hospitalization.  VE was estimated for 6 months after vaccination began (July-December) which included peak influenza detection months.  Logistic regression was used to evaluate the association between case status and vaccination while adjusting for age, province, medical conditions, and time. 

    Results: During July-December 2010 and 2011, 279 (18%) of 1545 patients were influenza virus positive, of whom 247 (89%) had influenza A and 32 (11%) had influenza B.  The median length of hospitalization for patients with influenza was 4 days (IQR 4-6), 4% had respiratory failure, and 2% died. Fourteen (5%) of 279 cases and 108 (9%) of 1266 controls were vaccinated against influenza.  Cases and controls did not differ in age (median 68 vs. 69 years, p=0.2) or presence of >=1 medical conditions (33% vs. 33%, p=0.9), but a larger proportion of cases were from one province (63% vs. 37%, p<0.01).     Unadjusted VE against hospitalization with influenza-associated ALRI was 43% (95% CI: 0%-68%); adjusted VE was 47% (5%-71%).  Influenza VE was not estimated by influenza type or smaller age strata due to insufficient numbers of cases.

    Conclusion: The 2010 and 2011 IIVs were moderately effective against hospitalization with influenza-associated ALRI among persons aged >=50 years, but vaccine coverage was low.  Additional efforts are warranted in Thailand to improve influenza vaccine uptake in this target group.

    Fatimah S. Dawood, MD1, Prabda Prapasiri2, Peera Areerat3, Asadang Ruayajin4, Malinee Chittaganpitch5, Charung Muangchana6, Henry C. Baggett7 and Sonja J. Olsen, PhD1,2, (1)Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, (2)Influenza Program, Thailand Ministry of Public Health-U.S. CDC Collaboration, Nonthaburi, Thailand, (3)Provincial Health Office, Nakhon Phanom, Thailand, (4)Provincial Health Office, Samut Prakan, Thailand, (5)National Institute of Health, Thailand Ministry of Public Health, Nonthaburi, Thailand, (6)Ministry of Public Health, National Vaccine Institute, Nonthaburi, Thailand, (7)International Emerging Infections Program, Global Disease Detection Center, Nonthaburi, Thailand


    F. S. Dawood, None

    P. Prapasiri, None

    P. Areerat, None

    A. Ruayajin, None

    M. Chittaganpitch, None

    C. Muangchana, None

    H. C. Baggett, None

    S. J. Olsen, None

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