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Chien Vien Chinh 1 Article
Persistence of vaccine-induced antibodies to A/H5N1 at 30 months and 36 months after vaccination in Vietnam
Chien Vien Chinh, Viet Phu Quoc, Loc Huynh Tan, Duoc Nguyen Van, Thai Pham Quang, Be Le Van
Epidemiol Health. 2021;43:e2021076.   Published online October 6, 2021
DOI: https://doi.org/10.4178/epih.e2021076
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Abstract
OBJECTIVES
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).
METHODS
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.
RESULTS
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.
CONCLUSIONS
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.
Summary
Korean summary
Key Message
A longitudinal un-controlled study followed participants enrolled in the phase II IVACFLU-A/ H5N1 vaccine trial in Ninh Hoa, Vietnam. The participants tested for anti-A/H5N1 IgG at baseline, 30 months, and 36 months after the complete vaccination to assess antibody status. 84.9% and 52.3% of the population have persistence of at least 1/10 of the A/H5N1 antibodies at 30 months and 36 months, respectively. Antibody persistence was higher in older people but lower in people who had experienced flu-like symptoms in the past or between 2 visits. The result can interpret that remarkable antibody persistence long after vaccination.

Epidemiol Health : Epidemiology and Health