Abstract
Objectives: To determine the status of immune responses after primary and booster immunization for SARS-CoV-2 variants and evaluate the differences in disease resistance based upon titers of neutralizing antibodies (NAbs) against the variants.
Methods: Participants aged 18-59 years received 2 doses of inactivated COVID-19 vaccine, 14 days apart, and a booster dose after 12 months. Blood samples were collected before vaccination (baseline), 1 and 6 months after primary immunization, and at multiple instances within 21 days of the booster dose. NAbs against the spike protein of Wuhan-Hu-1 and 3 variants were measured using pseudovirus neutralization assays.
Results: Of 400 enrolled participants, 387 completed visits scheduled within 6 months of the second dose and 346 participants received the booster dose in the follow-up research. After 1 month of primary immunization, geometric mean titers (GMTs) of NAbs peaked for Wuhan-Hu-1, whereas GMTs of other variants were <30. After 6 months of primary immunization, GMTs of NAbs against all strains were <30. After 3 days of booster immunization, GMTs were unaltered, seroconversion rates reached approximately 50% after 7 days, and GMTs of NAbs against all strains peaked at 14 days.
Conclusion: Two-dose of inactivated COVID-19 vaccine induced the formation of NAbs and memory-associated immune responses, and high titers of NAbs against the variants obtained after booster immunization may further improve the effectiveness of the vaccine.
Keywords: Inactivated COVID-19 vaccine; Primary and booster immunization; Pseudovirus neutralization assay; SARS-CoV-2 variants.
【저자키워드】 SARS-CoV-2 variants, Inactivated COVID-19 vaccine, Primary and booster immunization, Pseudovirus neutralization assay, 【초록키워드】 COVID-19, neutralizing antibody, COVID-19 vaccine, immune response, vaccination, Neutralizing antibodies, neutralization, variant, SARS-CoV-2 variant, immunization, variants, Spike protein, SARS-CoV-2 variants, immune responses, Wuhan, Research, Effectiveness, Follow-up, disease, booster dose, booster, Pseudovirus neutralization assay, inactivated, NAb, dose, strain, titers, geometric mean, within 6 months, Participants, Blood samples, status, second dose, other variants, NAbs, blood sample, geometric mean titers, GMTs, participant, seroconversion rates, seroconversion rate, geometric mean titer, Pseudovirus neutralization assays, Wuhan-Hu-1, IMPROVE, enrolled, collected, evaluate, peaked, determine, the spike protein, instance, reached, the vaccine, were measured, other variant, baseline, GMT, 【제목키워드】 SARS-CoV-2, immunogenicity,