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Influenza vaccination coverage and effectiveness in young children in Thailand, 2011-2013
Wanitchaya Kittikraisak1, Piyarat Suntarattiwong, Jens Levy
1Influenza Program, Thailand Ministry of Public Health - U.S. Centers for Disease Control and Prevention Collaboration, Nonthaburi, Thailand.
Insights
Influenza vaccination coverage in young Thai children remains low, but the vaccine demonstrated moderate effectiveness in preventing illness. Further efforts are crucial to enhance vaccination rates and assess vaccine effectiveness (VE) in this population.
Area of Science:
- Pediatric Infectious Diseases
- Vaccinology
- Public Health Surveillance
Background:
- Thailand recommends influenza vaccination for children aged 6 months to 2 years since 2009.
- No prior estimates of influenza vaccine coverage or effectiveness were available for this pediatric group.
Purpose of the Study:
- To estimate influenza vaccine coverage and effectiveness among children aged 36 months or younger in Thailand.
- To provide data to inform public health strategies for pediatric influenza prevention.
Main Methods:
- A 2-year prospective cohort study enrolled high-risk and healthy children up to 36 months of age.
- Acute respiratory illness (ARI) was monitored weekly, with influenza testing via real-time reverse transcription-polymerase chain reaction (RT-PCR).
- Vaccine effectiveness (VE) was calculated using the Cox proportional hazards model.
Main Results:
- Vaccination coverage was low, at 29.3% in 2011-2012 and 30.0% in 2012-2013.
- In 2011-2012, VE was 55% (95% CI, -72, 88); in 2012-2013, VE was 64% (95% CI, 13%, 85%).
- Influenza incidence was lower in vaccinated versus unvaccinated children in the second season.
Conclusions:
- Influenza vaccination coverage among young children in Thailand is low.
- The influenza vaccine demonstrated moderate effectiveness in this pediatric population.
- Increased vaccination coverage and ongoing evaluation of VE are necessary.
Background:
Since 2009, Thailand has recommended influenza vaccine for children aged 6 months through 2 years, but no estimates of influenza vaccine coverage or effectiveness are available for this target group.
Methods:
During August 2011-May 2013, high-risk and healthy children aged ≤36 months were enrolled in a 2-year prospective cohort study. Parents were contacted weekly about acute respiratory illness (ARI) in their child. Ill children had combined nasal and throat swabs tested for influenza viruses by real-time reverse transcription-polymerase chain reaction. Influenza vaccination status was verified with vaccination cards. The Cox proportional hazards approach was used to estimate hazard ratios. Vaccine effectiveness (VE) was estimated as 100% x (1-hazard ratio).
Results:
During 2011-2013, 968 children were enrolled (median age, 10·3 months); 948 (97·9%) had a vaccination record and were included. Of these, 394 (41·6%) had ≥1 medical conditions. Vaccination coverage for the 2011-2012 and 2012-2013 seasons was 29·3% (93/317) and 30·0% (197/656), respectively. In 2011-2012, there were 213 ARI episodes, of which 10 (4·6%) were influenza positive (2·3 per 1000 vaccinated and 3·8 per 1000 unvaccinated child-weeks). The VE was 55% (95% confidence interval [CI], -72, 88). In 2012-2013, there were 846 ARIs, of which 52 (6·2%) were influenza positive (1·8 per 1000 vaccinated and 4·5 per 1000 unvaccinated child-weeks). The VE was 64% (CI, 13%, 85%).
Conclusion:
Influenza vaccination coverage among young children in Thailand was low, although vaccination was moderately effective. Continued efforts are needed to increase influenza vaccination coverage and evaluate VE among young children in Thailand.
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