JMIR Publications

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:

The risk of new SARS-CoV-2 infections was assessed based on the number of vaccine doses, prior infections, and other clinic characteristics.

Methods:

We defined a cohort of 800 healthcare workers in a 24-month study (March 2020 to December 2022) in northern Barcelona to determine new infections against SARS-CoV-2.We used Extended Cox models, specifically Andersen and Gill (AG) and Prentice, Williams, and Peterson (PWP), 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, two PWP models were adjusted—one for those individuals with no or one infection and another for those with two or three infections—both with the same covariates as the AG model.

Results:

Participants with 1 to 4 vaccine doses had significantly lower infection risks than those without vaccination. Increasing the number of prior infections reduces the risk of infection by 75%. For those with none or one infection, receiving any vaccine dose led to a reduction in infection risk, while 2-3 chronic conditions and male gender increased the risk. Participants with a history of multiple infections (two or three) saw their risk influenced only by the administration of the 4th vaccine dose and specific job titles.

Conclusions:

The study suggests that both prior infections and vaccination status significantly contribute to SARS-CoV-2 immunity, supporting vaccine effectiveness in reducing infection 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 SARS-CoV-2 Clinical Trial: NCT04885478