Association Between COVID-19 Vaccination Status, Time Elapsed Since the Last Vaccine Dose, Morbidity, and Absenteeism among Healthcare Personnel: A Prospective, Multicenter Study

Aim: We assessed the impact of COVID-19 vaccination status and time elapsed since the last vaccine dose on morbidity and absenteeism among healthcare personnel (HCP) in the context of a mandatory vaccination policy. Methods: We followed 7592 HCP from November 15, 2021 through April 17, 2022. Full COVID-19 vaccination was defined as a primary vaccination series plus a booster dose at least six months later. Results: There were 6496 (85.6 %) fully vaccinated, 953 (12.5 %) not fully vaccinated, and 143 (1.9 %) unvaccinated HCP. A total of 2182 absenteeism episodes occurred. Of 2088 absenteeism episodes among vaccinated HCP with known vaccination status, 1971 (94.4 %) concerned fully vaccinated and 117 (5.6 %) not fully vaccinated. Fully vaccinated HCP had 1.6 fewer days of absence compared to those not fully vaccinated (8.1 versus 9.7; p-value < 0.001). Multivariable regression analyses showed that full vaccination was associated with shorter absenteeism compared to not full vaccination (OR: 0.56; 95 % CI: 0.36-0.87; p-value = 0.01). Compared to a history of <= 17.1 weeks since the last dose, a history of > 17.1 weeks since the last dose was associated with longer absenteeism (OR: 1.22, 95 % CI:1.02-1.46; p-value = 0.026) and increased risk for febrile episode (OR: 1.33; 95 % CI: 1.09-1.63; p-value = 0.004), influenza-like illness (OR: 1.53, 95 % CI: 1.02-2.30; p-value = 0.038), and COVID-19 (OR: 1.72; 95 % CI: 1.24-2.39; pvalue = 0.001). Conclusions: The COVID-19 pandemic continues to impose a considerable impact on HCP. The administration of a vaccine dose in less than four months before significantly protected against COVID-19 and absenteeism duration, irrespective of COVID-19 vaccination status. Defining the optimal timing of boosters is imperative.