COVID 19 Incidence rates were not different among high risk health-care workers and non-health workers after SARS-CoV-2 vaccination: a prospective study in Cali-Colombia

ABSTRACT

Background. The seroprevalence of COVID-19 among health-care workers (HCWs) is still not well characterized in Latin America and the Caribbean. The objective of this study was to compare incidence rates (IR) during the COVID-19 pandemic among HCWs vs. non-HCWs in a university hospital in Cali, Colombia. (Table Presented) Methods. A prospective study was performed. The study included two groups HCWs with high-risk contact of SARS-CoV-2 infections vs. administrative hospital workers (non-HCW). Seroprevalence of SARS-CoV-2 antibodies between both groups was compared according to vaccination history and confirmed SARS-CoV-2 infection during follow-up (March 6th, 2020, to February 28th, 2022). The study was developed in three phases according to the infection waves in Colombia, measuring antibodies anti-nucleocapsid and anti-spike serum concentration in each one. A descriptive analysis was done to compare both groups and IR per month (Figure 1). Results. 480 participants were included, 291 (60.6%) were HCWs, and 189 (39.4%) were non-HCWs. After the second wave and before vaccination, the accumulative seroprevalence was 40.6% 49.1% of HCWs vs. 27.5% of non-HCWs (p< 0.001). 9.2% of HCWs and 7.9% of non-HCWs seropositive individuals had an asymptomatic infection (p=0.447). Of the 51.9% of susceptible HCWs and 72.5% of susceptible non-HCWs before the third wave, the risk of developing SARS-CoV-2 infection was 9.2% and 12.8%, respectively. After 24 months, the infection rate was higher in HCWs and non-HCWs (55.6% vs. 41.9%, p< 0.001) (Figure 2). The total IR was 31.4/1,000 person-month, with an IR difference of 21/1,000 person-month being higher in HCWs comparing non-HCWs (40.7 vs. 19.8, p< 0.001), but after vaccination (April 2021), the IR difference was not significative (IR difference 5%, p=0.1605). The asymptomatic disease was 9.8% of HCWs vs. 10.2% of non-HCWs. Since vaccination, 93.6% of workers had positive anti-S antibodies after 2 doses;and 100% had them after 3rd dose. SARS-CoV-2 Omicron variant increased cases during the fourth wave, more in non-HCWs. Conclusion. Before vaccination, HCWs had higher infection rates, mainly after the second wave. However, after the immunization, the IR in both groups significantly decreased and equalized in both groups.