Severity of COVID-19 Infection Versus Reinfection, Before and After Vaccination

There are still many unanswered questions surrounding the severity of COVID-19 infection. As vaccine protection wanes and breakthrough infections become more common, the UK Health Security Agency sought to determine whether the severity of COVID-19 infections is affected by vaccination and/or prior infection.

The research was presented during the 32nd European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), held in Lisbon, Portugal from April 23-26, 2022. The investigators utilized data from the SARS-CoV-2 Immunity and Reinfection Evaluation (SIREN) study to conduct their analysis. The study participants provided COVID-19 symptom information via questionnaires and PCR tests, completed every 2 weeks.

The study cohort were categorized by whether they had a primary COVID-19 infection or reinfection, and whether this occurred before or after vaccination. “Reinfection” was defined as a positive PCR test either 90 days after an initial PCR-positive sample, or 28 days after an antibody positive sample.

From February 1, 2020-November 30, 2021, a total of 8434 participants were included in the study. The investigators conducted descriptive analysis to investigate the differences between the participants as related to symptom type, duration, and number, as well as hospitalization and cycle threshold (CT) values.

Overall, a higher proportion of participants had COVID-19 symptoms during primary infection than during reinfection. The results showed that 69.5% of participants had a symptomatic primary COVID-19 infection before they were vaccinated, whereas 55.2% had a symptomatic primary infection after vaccination. Among the cohort who experienced reinfection, 23.5% had symptomatic infection before vaccination, and 33.9% were symptomatic after vaccination.

Participants also reported a longer duration and higher number of symptoms during primary infection than during reinfection. The proportion of hospitalizations were higher during both primary infection and pre-vaccination. Additionally, CT values were lower during primary infection than during reinfection.

The investigators concluded that COVID-19 primary infections were more severe than reinfections. They also found infections were more severe when unvaccinated than once vaccinated against COVID-19. “These findings add additional support for supporting national vaccination programs, as vaccinations can contribute to protection against severe infection,” the study authors wrote.

The SARS-CoV-2 Immunity and Reinfection Evaluation (SIREN) study is a prospective cohort study of healthcare workers in the United Kingdom. It currently includes more than 44000 National Health Service workers from 135 hospitals across the UK. Upon study recruitment, the cohort had high seropositivity; 30% of the healthcare workers had contracted COVID-19 before the second wave. More than 95% of the cohort is now fully vaccinated. Participants under active follow-up undergo asymptomatic COVID-19 PCR testing every 2 weeks.

This study, “Is the severity of SARS-CoV-2 infections affected by vaccination and prior infection status? A comparative case-series analysis within the UK SIREN cohort study,” was presented at the 32nd European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), held April 23-26, 2022 in Lisbon, Portugal.