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Epidemiol Health > Volume 43; 2021 > Article
Epidemiology and Health 2021;43: e2021076-0.
DOI: https://doi.org/10.4178/epih.e2021076    Published online Oct 6, 2021.
Persistence of vaccine-induced antibodies to A/H5N1 at 30 months and 36 months after vaccination in Vietnam
Chien Vien Chinh1,2  , Viet Phu Quoc3  , Loc Huynh Tan4  , Duoc Nguyen Van1  , Thai Pham Quang5,6  , Be Le Van1 
1Institute of Vaccines and Medical Biologicals (IVAC), Nha Trang, Vietnam
2Tay Nguyen Institute of Hygiene and Epidemiology, Buon Me Thuot, Vietnam
3Khanh Hoa Medical Service, Nha Trang, Vietnam
4Ninh Hoa District Medical Center, Khanh Hoa, Vietnam
5National Institute of Hygiene and Epidemiology, Hanoi, Vietnam
6School of Preventive Medicine and Public Health, Hanoi Medical University, Hanoi, Vietnam
Correspondence  Chien Vien Chinh ,Email: chienvc66@yahoo.com
Received: Apr 7, 2021  Accepted after revision: Oct 6, 2021
An A/H5N1 vaccine (IVACFLU-A/H5N1) was accepted for use in Vietnam; however, antibody persistence after vaccination has not been well characterized. We examined post-vaccination antibody persistence and related risk factors in individuals enrolled in the phase II IVACFLU-A/ H5N1 vaccine trial in Ninh Hoa, Vietnam, who received a 15-μg dose (2 injections 21 days apart).
We used a longitudinal study design to follow 86 participants, without a control group. The participants tested as anti-A/H5N1 immunoglobulin G seronegative at baseline and received both doses of the vaccine. Blood was drawn at 30 months and 36 months after the complete vaccination to assess antibody status. Antibody persistence status was compared by demographic characteristics and exposure risk factors using univariate logistic regression.
In total, 84.9% and 52.3% of the population showed persistence of at least 1/10 of the A/H5N1 antibodies at 30 months and 36 months after IVACFLU-A/H5N1 vaccination, respectively. The odds of antibody persistence were higher in older people, but lower in people who had experienced flu-like symptoms in the past 18 months or between 2 visits. We recorded no differences between A/H5N1 antibody persistence and exposure risk factors, including having a poultry farm, coming into contact with poultry, and slaughtering and processing poultry.
This study demonstrated noteworthy antibody persistence, indicated by the seroconversion rate and geometric mean titer at 30 months and 36 months after the IVACFLU-A/H5N1 vaccine. Further studies should investigate older people and those who experienced flu-like symptoms to determine a suitable time for a booster shot.
Keywords: Antibody persistence, Influenza A/H5N1, Vietnam, Influenza vaccine
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