The Dynamic Risk of COVID-19-Related Events in Vaccinated Healthcare Workers (HCWs) from a Tertiary Hospital in Bucharest, Romania: A Study Based on Active Surveillance Data

Abstract

Our study describes the frequency and severity of COVID-19 in HCWs and estimates the dynamic risk of COVID-19-related events. We actively surveyed all HCWs from a tertiary infectious disease hospital from 26 February 2020 to 31 May 2023. Of 1220 HCWs, 62.9% (767) had at least one COVID-19 episode. The under 29 years (p = 0.0001) and 40–49 years (p = 0.01) age groups, nurses (p = 0.0001), and high-risk departments (p = 0.037) were characteristics significantly more frequent in HCWs with COVID-19 history. A higher percentage of boosters (53.2%; p < 0.0001) were registered in the uninfected group. The second episode of COVID-19 was significantly milder than the first. Data regarding clinical outcomes from 31 January 2021 to 31 May 2023 were analyzed in a follow-up study to determine the risk of COVID-19-related events. The Cox regression analysis revealed that HCWs with booster shots had a lower risk of COVID-19 across all events, symptomatic events, and moderate to severe events as adjusted hazard ratio (aHR) were: 0.71 (95%CI: 0.54–0.96), 0.23 (95%CI: 0.12–0.46), and 0.17 (95%CI: 0.07–0.43), respectively. Within the vaccinated subgroup, the HCWs with hybrid immunity and booster had aHR for all followed-up events of 0.42 (95%CI: 0.30–0.58), for symptomatic events of 0.52 (95%CI: 0.36–0.74), and 0.15 (95%CI: 0.03–0.66) for moderate to severe events. The risk of COVID-19 clinical events was lower for HCWs with at least one booster than those completely vaccinated.

Hybrid Immunity and the Incidence of SARS-CoV-2 Reinfections during the Omicron Era in Frontline Healthcare Workers

“…Natural and artificial immunity has been assessed by evaluating the dynamics of protective antibodies over time or by using epidemiological indicators from surveillance data. Both types of study have shown that natural and artificial immunity both wane over time and have led to the adaptation of recommendations regarding vaccination schedules [ 8 , 17 , 19 , 27 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. Common epidemiological indicators of frequency in other studies showed increases in the number of reinfections and primo-infections in the Omicron era, similar to our study [ 25 , 26 , 43 , 44 ].…”

“…In terms of disease history, published studies have supported the importance of hybrid immunity [ 19 , 39 , 49 ]. The study ORCHESTRA compared subjects re-vaccinated with the first booster and a history of SARS-CoV-2 infection with subjects with no prior infection, and the relative risk ratio was 0.11 (95% CI: 0.05–0.25).…”

“…A cohort retrospective study of HCWs showed a rate of reinfection of 16.2% (95% CI: 13.5–19.3%) in the hybrid immunity group compared with HCWs with no prior infection, which registered a rate of reinfection of 41.7% (95% CI: 40.3–43.0%). In our cohort, surveillance data demonstrated an advantage in terms of protection in individuals with hybrid immunity compared with HCWs vaccinated with the primary schedule and no prior infection, with a hazard ratio (HR) across all COVID-19 events of 0.6 (95% CI: 0.47–0.77) [ 19 ]. The HCWs with hybrid immunity and first booster compared to HCWs vaccinated with the primary schedule and no prior infection had a HR of 0.42 (95% CI: 0.30–0.58) [ 19 ].…”

“…The current study continues and complements previous research on the risk of COVID-19 in HCWs in a designated hospital for treating COVID-19 patients in Bucharest, Romania. The previously published research evaluated the clinical outcome in relation to nonpharmacological protective measures, vaccination, and individual risk [ 18 , 19 ]. Data showed that risk factors associated with the severity of the first SARS-CoV-2 infection were exposure to COVID-19 confirmed cases, age, obesity and anemia [ 18 ].…”

“…Data showed that risk factors associated with the severity of the first SARS-CoV-2 infection were exposure to COVID-19 confirmed cases, age, obesity and anemia [ 18 ]. The risk of COVID-19 across all clinical events was lower in HCWs with the first booster administered compared with the risk in HCWs with the primary schedule or who were nonvaccinated [ 19 ].…”