Immunogenicity of Oxford-AstraZeneca COVID-19 Vaccine in Vietnamese Health-Care Workers

Abstract

We studied the immunogenicity of the Oxford-AstraZeneca vaccine in health-care workers of a major infectious diseases hospital in Vietnam. We measured neutralizing antibodies before and 14 days after each dose, and at day 28 and month 3 after dose 1. A total of 554 workers (136 men and 418 women; age range, 22-71 years; median age, 36 years) participated with the study. Of the 144 participants selected for follow-up after dose 1, 104 and 94 gave blood for antibody measurement at weeks 6 and 8, and at month 3 after dose 1, respectively. The window time between the two doses was 6 weeks. At baseline, none had detectable neutralizing antibodies. After dose 1, the proportion of participants with detectable neutralizing antibodies increased from 27.3% (151 of 554) at day 14 to 78.0% (432 of 554) at day 28. Age correlated negatively with the development and the levels of neutralizing antibodies. However, at day 28, these differences were less profound, and women had a greater seroconversion rate and greater levels of neutralizing antibodies than men. After dose 2, these age and gender associations were not observable. In addition, the proportion of study participants with detectable neutralizing antibodies increased from 70.2% (73 of 104) before dose 2 (week 6, after dose 1) to 98.1% (102 of 104) 14 days later. At month 3, neutralizing antibodies decreased and 94.7% (89 of 94) of the study participants remained seropositive. The Oxford-AstraZeneca COVID-19 vaccine is immunogenic in Vietnamese health-care workers. These data are critical to informing the deployment of the COVID-19 vaccine in Vietnam and in Southeast Asia, where vaccination coverage remains inadequate.

Figure 1.

Development of neutralizing antibodies levels after vaccination. (A) Neutralizing antibody levels measured at 2 and 4 weeks after the first dose was administered to 554 study participants. (B) Neutralizing antibody levels measured at time points from baseline to month 3 after the first dose was administered to the subgroups. Data on neutralizing antibody levels obtained from 11 convalescent sera collected during weeks 4 through 7 (right column) from cases with mild or asymptomatic infection were included as references.

Figure 2.

The associations between neutralizing antibody level and age. (A) Association between age and the probabilities of having detectable neutralizing antibodies at 2 and 4 weeks after the first does was administered to 554 study participants. (B) Association between age and neutralizing antibody levels measured at 2 and 4 weeks after the first dose was administered to 554 study participants. Black circles represent data for the 14-day time point; gray circles represent data for 28-day time point. Shaded areas indicate 95% CIs.

Figure 3.

Neutralizing antibody levels of participants selected to assess the impact of the second dose. (A) Two and 4 weeks after the first dose (n = 104). (B) Before the second dose (6 weeks after the first dose) and 2 weeks after the second dose (n = 104). (C) At month 3 after the first dose (n = 94). Shaded areas indicate 95% CIs.