Effectiveness of the severe acute respiratory syndrome coronavirus 2 Omicron BA.5 bivalent vaccine on symptoms in healthcare workers with BA.5 infection.

Background: The infection status of healthcare workers (HCWs) with coronavirus disease 2019 has become a major concern worldwide. In this study, we investigated the efficacy of the number of vaccine doses on symptoms after BA.5-adapted bivalent vaccination in HCWs. Methods: We analyzed the occupation, route of infection, symptoms, and vaccination history of all HCWs who tested positive for severe acute respiratory syndrome coronavirus 2 and worked in our hospital from November 2020 to March 2023. A logistic regression analysis was performed to examine the association between the presence of BA.5-adapted bivalent vaccination and symptoms. Results: During the observation period, 531 HCWs became infected. Of these, 72 % were women, with a median age of 30 years. Nurses accounted for 57 % of the infected cases, and many of the infection routes were from family members. We examined the relationship between symptoms in 352 HCWs infected with the Omicron BA.5* variant and the number of vaccine doses. As the number of vaccine doses increased, the rate of fever decreased, while symptoms such as a runny nose and sore throat tended to increase. The logistic regression analysis showed that the rate of fever tended to decrease (odds ratio = 0.52, 95 % confidence interval: 0.26-1.01, p = 0.056) and that of a runny nose increased (odds ratio = 3.68, 95 % confidence interval: 1.17-10.6, p = 0.018) after BA.5-adapted bivalent vaccination. Conclusion: This study shows that fever is reduced and mild symptoms are increased after BA.5-adapted bivalent vaccination in BA.5-infected HCWs. This result highlights the potential effectiveness of tailored vaccination strategies in the management of emerging COVID-19 variants.

Antibody Response to the BA.5 Bivalent Vaccine Shot: a Two-Year Follow-Up Study following Initial COVID-19 mRNA Vaccination.

Although many studies have been conducted on the increase in spike antibody levels after vaccination, there is insufficient prospective and longitudinal information on the BA.5-adapted bivalent vaccine up to the fifth vaccination. In this study, we conducted a follow-up study of spike antibody levels and infection history in 46 health care workers who received up to 5 vaccinations. Monovalent vaccines were administered for the first to fourth vaccinations, and a bivalent vaccine was administered for the fifth vaccination. 11 serum samples were collected from each participant, and antibody levels were measured in a total of 506 serum samples. During the observation period, 43 of the 46 health care workers had no infection history, and 3 had a history of infection. Spike antibody levels peaked at 1 week after the second booster vaccination and gradually declined until the 27th week after the second vaccination. After 2 weeks following the fifth BA.5-adapted bivalent vaccine, the spike antibody levels significantly increased (median: 23,756 [IQR: 16,450 to 37,326]), compared to those measured before vaccination (median: 9,354 [IQR: 5,904 to 15,784]) (paired Wilcoxon signed-rank test, P = 5.7 × 10-14). These changes in antibody kinetics were observed regardless of age or sex. These results suggest that booster vaccination increased the spike antibody levels. Regular vaccination is effective in maintaining long-term antibody levels. IMPORTANCE A COVID-19 bivalent mRNA vaccine was developed and administered to health care workers. The COVID-19 mRNA vaccine induces a robust antibody response. However, little is known about the antibody response to vaccines in serially collected blood samples from the same individuals. Here, we provide two-year follow-up data on the humoral immune response to COVID-19 mRNA vaccines in health care workers who received up to five vaccinations, including the BA.5-adapted bivalent vaccine. The results suggest that regular vaccination is effective in maintaining long-term antibody levels and have implications for vaccine efficacy and booster dose strategies in health care settings.

Robust Antibody Responses to the BNT162b2 mRNA Vaccine Occur Within a Week After the First Dose in Previously Infected Individuals and After the Second Dose in Uninfected Individuals.

Background: Vaccines against severe acute respiratory syndrome coronavirus 2 can trigger acquired immunity in infection-naïve individuals and offer a path toward ending the coronavirus disease pandemic that began in 2019. However, the kinetics of early antibody responses in vaccinated individuals remain poorly understood. Method: We followed BNT162b2 mRNA-vaccinated health care workers (HCWs, N=108) including 103 infection-naïve and five previously infected individuals. A total of 763 blood samples were collected weekly or hourly basis before and after vaccination. Serological analysis of anti-spike and anti-nucleocapsid antibodies was performed. Results: Seroconversion occurred in all infection-naïve HCWs 3 weeks after the first dose (just before the second vaccination) and a marked boosting effect was observed at 4 weeks (1 week after the second dose). Among previously infected HCWs with pre-existing antibodies against the spike protein, a remarkable boosting effect was observed during the first week after vaccination, and a further increase in antibody titres was observed after the second dose. In one previously infected patient, daily blood sampling was conducted. Antibody titres began to increase 96 hours (4 days) after the first dose. Conclusion: The BNT162b2 mRNA vaccine remarkably enhanced antibody responses after the second dose in infection-naïve individuals and after the first dose in previously infected HCWs of all ages and genders. Antibody titres decreased slightly after the 5th week post-vaccination. The robust boosting effect of immunisation suggests that increased antibody titres following exposure to the virus may restrict viral replication, prolong the incubation period, or lessen the severity of disease.