Herd immunity among healthcare workers of high-risk units in a Northern Italy hospital in 2017

Background: Vaccination of healthcare workers (HCWs) is a fundamental practice aimed to protect both patients and professionals from vaccine preventable diseases (VPDs), as well as healthcare institutions from service breakdowns. This study evaluated coverage among HCWs in high-risk units as three measles and eight varicella cases occurred at Udine University Hospital from January 2015 to September 2017. Methods: Age, gender, working unit and coverage of HCWs against selected VPDs (measles, mumps, rubella, varicella, hepatitis B) were obtained in September 2017 from Occupational Health records. High-risk units identified were: emergency and internal medicine (EIM), intensive care, rheumatology and infectious diseases, maternal and child health (MCH). Specific protective antibody titers and recommended vaccine doses were considered as evidence of protection. Data were stratified by gender, profession and unit. Chi square/Fisher’s test was used with an α-level of 0.05. Results: HCWs involved were 925: mean age 43 years; 741 females (80%); 193 were doctors (21%), 517 nurses (56%), 212 other (23%), 3 not declared; they worked mostly in EIM (368; 40%) and in MCH (289; 31%). Considering specific available data, global coverage was 93.5% for measles, 87.4% for mumps, 92.3% for rubella, 97.8% for varicella, 90.2% for hepatitis B. Coverage was higher in women for rubella and varicella (both p < 0.005); MCH units reached 95.5% for measles and rubella (p = 0.009). No differences were found by profession. HCWs certainly unprotected for at least one VPD were 232 (25%). Conclusions: Global coverages for measles, mumps and rubella do not reach 95% requirement for herd immunity; one tenth of HCWs is prone to hepatitis B. Coverage of MCH professionals suggests a greater awareness of VPD associated risks compared to other units. Monitoring the proportion of unprotected HCWs is critical to prevent new outbreaks, thus advocating for continuous coverage analyses and proactive vaccine offering. Key messages: Continuous monitoring of HCWs’ immunological status would allow to support herd immunity protection for susceptible individuals in healthcare settings. High-risk units should be prioritized when implementing actions to restore or maintain immunization levels, in order to effectively control and prevent unexpected outbreaks.