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. 2024 Nov 22:10:e56926.
doi: 10.2196/56926.

SARS-CoV-2 Infection Risk by Vaccine Doses and Prior Infections Over 24 Months: ProHEpiC-19 Longitudinal Study

Pere Torán-Monserrat  1   2   3   4 , Noemí Lamonja-Vicente  1 , Anna Costa-Garrido  1 , Lucía A Carrasco-Ribelles  1   5 , Bibiana Quirant  6   7   8 , Marc Boigues  6   7   8 , Xaviera Molina  9   10 , Carla Chacón  1 , Rosalia Dacosta-Aguayo  1 , Fernando Arméstar  11 , Eva María Martínez Cáceres #  6   7   8 , Julia G Prado #  2   12   13 , Concepción Violán #  1   5   8   14   15 ; ProHEpiC-19 study group  16
Collaborators, Affiliations

SARS-CoV-2 Infection Risk by Vaccine Doses and Prior Infections Over 24 Months: ProHEpiC-19 Longitudinal Study

Pere Torán-Monserrat et al. JMIR Public Health Surveill. .

Abstract

Background: As the vaccination campaign against COVID-19 progresses, it becomes crucial to comprehend the lasting effects of vaccination on safeguarding against new infections or reinfections.

Objective: This study aimed to assess the risk of new SARS-CoV-2 infections based on the number of vaccine doses, prior infections, and other clinical characteristics.

Methods: We defined a cohort of 800 health care workers in a 24-month study (March 2020 to December 2022) in northern Barcelona to determine new infections by SARS-CoV-2. We used extended Cox models, specifically Andersen-Gill (AG) and Prentice-Williams-Peterson, and we examined the risk of new infections. The AG model incorporated variables such as sex, age, job title, number of chronic conditions, vaccine doses, and prior infections. Additionally, 2 Prentice-Williams-Peterson models were adjusted, one for those individuals with no or 1 infection and another for those with 2 or 3 infections, both with the same covariates as the AG model.

Results: The 800 participants (n=605, 75.6% women) received 1, 2, 3, and 4 doses of the vaccine. Compared to those who were unvaccinated, the number of vaccine doses significantly reduced (P<.001) the risk of infection by 66%, 81%, 89%, and 99%, respectively. Unit increase in the number of prior infections reduced the risk of infection by 75% (P<.001). When separating individuals by number of previous infections, risk was significantly reduced for those with no or 1 infection by 61% (P=.02), and by 88%, 93%, and 99% (P<.001) with 1, 2, 3, or 4 doses, respectively. In contrast, for those with 2 or 3 previous infections, the reduction was only significant with the fourth dose, at 98% (P<.001). The number of chronic diseases only increased the risk by 28%-31% (P<.001) for individuals with 0-1 previous infections.

Conclusions: The study suggests that both prior infections and vaccination status significantly contribute to SARS-CoV-2 immunity, supporting vaccine effectiveness in reducing risk of reinfection for up to 24 months after follow-up from the onset of the pandemic. These insights contribute to our understanding of long-term immunity dynamics and inform strategies for mitigating the impact of COVID-19.

Keywords: COVID-19; SARS-CoV-2; cohort; coronavirus; epidemiological; epidemiology; extended Cox models; health care workers; infectious; longitudinal; respiratory; risks; vaccinated; vaccination; vaccines.

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Conflict of interest statement

Conflicts of Interest: All authors have completed the ICMJE Uniform Disclosure Form and declare no support from any organization for the submitted work other than those detailed in the Acknowledgments section. All other authors declare no competing interests.

Figures

Figure 1.
Figure 1.. Flowchart of the study population. The figure reports the participant’s entry into the study, the number of individuals who met each exclusion criterion, and the number of individuals that met all the inclusion criteria.
Figure 2.
Figure 2.. SARS-CoV-2 infection hazard ratios as calculated by the Andersen-Gill model. Note: The model uses a common baseline risk function and accounts for a time-dependent variable (number of infections). The number of chronic diseases was calculated using the operational definition of the Swedish National Study of Aging and Care in Kungsholmen. Statistical significance (P<.05) is denoted in bold. Ref: reference group.
Figure 3.
Figure 3.. SARS-CoV-2 infection hazard ratios as calculated by the Prentice-Williams-Peterson models. Note: One of the models includes the participants with no or 1 infection, and the other those with 2 or 3 infections. The number of chronic diseases was calculated using the operational definition of the Swedish National Study of Aging and Care in Kungsholmen. Statistical significance (P<.05) is denoted in bold. Ref: reference group.
See this image and copyright information in PMC

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