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Do previously infected individuals still benefit from vaccination against COVID-19?

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In a recent study published in pros medicine, researchers determined the vaccine efficacy (VE) of a primary coronavirus disease 2019 (COVID-19) vaccination series. They determined VE for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection, COVID-19-related hospitalization, and mortality. In this way, researchers evaluated the impact of time post-vaccination during the predominance era of different SARS-CoV-2 variants, namely alpha, delta, and omicron.

study: Vaccine efficacy against SARS-CoV-2 reinfection during periods of alpha, delta, or omicron predominance: a Danish national studyImage Credit: LookerStudio/Shutterstock

Background

In Denmark, the government is providing free COVID-19 tests, vaccines and medical care to all residents. They said in December 2020 he rolled out a COVID-19 vaccination program, prioritizing the elderly and those at higher risk of severe illness. Likewise, they have launched a booster vaccination program in September 2021.

Scientific data show reduced efficacy of COVID-19 vaccines against Omicron (B.1.1.529) variants. Studies have shown that innate immunity is more effective in preventing SARS-CoV-2 reinfection than vaccination. It is therefore of public health interest to examine the additional benefits, if any, of vaccination among previously infected individuals with SARS-CoV-2.

About research

In this study, investigators used four national databases: the Danish Civil Registry System (CRS), the Danish Microbiology Database (MiBa), the Danish Vaccination Register (DVR), and the Danish National Patient Register (DNPR). Data were compiled from various sources.

Combined with the unique personal registration number of Danish citizens, this data will help identify people with confirmed SARS-CoV-2 infections between 1 January 2020 and 31 January 2022. It was helpful. CSR data are defined as time periods in which variants accounted for ≥75% of whole-genome sequence reverse transcription-polymerase chain reaction (RT-PCR) tests. In addition, the team investigated her COVID-19-related hospitalization up to 14 days or 48 hours before his SARS-CoV-2 reinfection and her death within 30 days of reinfection.

In statistical analyses, we included gender, comorbidities, and country of origin as categorical variables, and age and length of hospitalization as time-varying covariates. The team used quasi-Poisson regression models to estimate crude incidence rate ratios (IRRs) and Cox proportional hazards regression models, adjusted for all variables at each pre- and post-vaccination period. hazard ratios (HR) were estimated. Finally, they calculated the VE crude oil (VEcrude oil) and adjusted (VEAdjusted) as a percentage using IRR and HR values.

Survey results

The study population consisted of 209,814, 292,978, and 245,530 individuals infected before or during the alpha-, delta-, and omicron-dominant eras, respectively. Of these, 19.2%, 64.9%, and 64.6% of people had received her first dose of COVID-19 during alpha, delta, and omicron, respectively. The main finding was that previously infected individuals also benefited from COVID-19 vaccination in all three different time periods, an important finding for policy makers to plan future vaccination strategies. Data.

During periods of alpha dominance, VE was not statistically significant. It peaked at 71% at 104 days or more after vaccination, regardless of the type of COVID-19 vaccine. However, VE against reinfection was highest 14 to 43 days after the primary vaccination series in the Delta (94%) and Omicron (60%) periods. Researchers noted an early VE of 60% against reinfection, even during the Omicron period, although lower than other variants. These results are consistent with the Qatar study showing a 55.1% VE against reinfection with Omicron after two doses of COVID-19 mRNA vaccine.

Older and more vulnerable populations were preferentially vaccinated against SARS-CoV-2. These individuals had slower post-vaccination immune responses, explaining why the observed VE was not statistically significant during the alpha period. age group with SARS-CoV-2 reinfection experienced more severe outcomes overall and within the same variant time period.

Another interesting finding was that the risk of COVID-19-related hospitalization during the alpha period was higher for vaccinated and non-vaccinated individuals (IR: 0.002 vs. 0.001). Presumably even before the vaccine deployment, some long-term care facility (LTCF) residents had already contracted SARS-CoV-2 infection, and the current study shows hospitalization and death due to complications from COVID-19. There were too few events for researchers to estimate the same his VE.

The completeness of the Danish registry data may have removed any unmeasured biases that may have influenced the study results. However, studies with longer follow-up can confirm her VE for severe COVID-19 outcomes in previously infected people.

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