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. 2024 Sep 17;12(9):1057.
doi: 10.3390/vaccines12091057.

Evaluation of Vaccine Strategies among Healthcare Workers during COVID-19 Omicron Outbreak in Taiwan

Min-Ru Lin  1   2 , Chung-Guei Huang  3   4 , Cheng-Hsun Chiu  1   2   5 , Chih-Jung Chen  1   2   5
Affiliations

Evaluation of Vaccine Strategies among Healthcare Workers during COVID-19 Omicron Outbreak in Taiwan

Min-Ru Lin et al. Vaccines (Basel). .

Abstract

Background/objectives: This study aimed to assess the reactogenicity and immunogenicity of various SARS-CoV-2 vaccines and compare their protective effects against COVID-19 among healthcare workers (HCWs) during the Omicron outbreak in Taiwan.

Methods: Conducted from March 2021 to July 2023, this prospective observational study included healthy HCWs without prior COVID-19 immunization. Participants chose between adenovirus-vectored (AstraZeneca), mRNA (Moderna, BioNTech-Pfizer), and protein-based (Medigen, Novavax) vaccines. Blood samples were taken at multiple points to measure neutralizing antibody (nAb) titers, and adverse events (AEs) were recorded via questionnaires.

Results: Of 710 HCWs, 668 (94.1%) completed three doses, and 290 (40.8%) received a fourth dose during the Omicron outbreak. AEs were more common with AstraZeneca and Moderna vaccines, while Medigen caused fewer AEs. Initial nAb titers were highest with Moderna but waned over time regardless of the vaccine. Booster doses significantly increased nAb titers, with the highest levels observed in Moderna BA1 recipients. The fourth dose significantly reduced COVID-19 incidence, with Moderna BA1 being the most effective.

Conclusions: Regular booster doses, especially with mRNA and adjuvant-protein vaccines, effectively enhance nAb levels and reduce infection rates, providing critical protection for frontline HCWs during variant outbreaks.

Keywords: COVID-19; effectiveness; immunogenicity; reactogenicity; vaccine.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Timelines of the COVID-19 outbreaks and the introduction of various COVID-19 vaccines in Taiwan. The study period and the temporal relationship of vaccine doses administered to the healthcare workers in the study are also shown. The data of daily COVID-19 confirmed cases in Taiwan are available at https://covid-19.nchc.org.tw/2023_city_confirmed.php (accessed on 18 August 2024).
Figure 2
Figure 2
Flow chart of case enrollment and numbers of subjects on different vaccines at dose 1, 2, 3 and 4 against COVID-19.
Figure 3
Figure 3
The rates of solicited adverse events of immunization against COVID-19 within seven days of doses 1 (a), 2 (b), 3 (c), and 4 (d).
Figure 4
Figure 4
Humoral immunogenicity of vaccines against COVID-19 in healthcare workers. (a) The geometric mean titers (GMTs) of neutralizing antibodies (nAb) against the SARS-CoV-2 ancestral strain in eight groups of healthcare workers on different vaccination schedules on five occasions, including before vaccination (Pre V1), before the 2nd dose of vaccination (Pre V2), 30 days after the 2nd dose of vaccination (30 days post V2), before the 3rd dose of vaccination (Pre V3), and 30 days post the 3rd vaccination (30 days post V3). (b) The comparisons of GMTs evoked by different vaccines on five occasions. (c) The nAb before the fourth dose of vaccine (Pre V4) and 30 days after dose 4 (30 days post V4). The comparisons of post-immunization GMTs were made between Moderna vaccine recipients and those on the other four vaccines. Categorical variables were compared using the Chi-square or Fisher’s exact tests. For non-categorical variables, a one-way independent analysis of variance was used, followed by post hoc analysis.
Figure 4
Figure 4
Humoral immunogenicity of vaccines against COVID-19 in healthcare workers. (a) The geometric mean titers (GMTs) of neutralizing antibodies (nAb) against the SARS-CoV-2 ancestral strain in eight groups of healthcare workers on different vaccination schedules on five occasions, including before vaccination (Pre V1), before the 2nd dose of vaccination (Pre V2), 30 days after the 2nd dose of vaccination (30 days post V2), before the 3rd dose of vaccination (Pre V3), and 30 days post the 3rd vaccination (30 days post V3). (b) The comparisons of GMTs evoked by different vaccines on five occasions. (c) The nAb before the fourth dose of vaccine (Pre V4) and 30 days after dose 4 (30 days post V4). The comparisons of post-immunization GMTs were made between Moderna vaccine recipients and those on the other four vaccines. Categorical variables were compared using the Chi-square or Fisher’s exact tests. For non-categorical variables, a one-way independent analysis of variance was used, followed by post hoc analysis.
Figure 5
Figure 5
The Kaplan–Meier curves depict the probabilities of individuals remaining free from COVID-19 following their initial immunization against SARS-CoV-2. Subgroups were formed based on the administration of a fourth vaccine dose (immunized versus not immunized) (a) and the specific type of the vaccines among the dose 4 vaccine recipients (b).
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