Infection of healthcare workers despite a high vaccination rate during the fifth wave of COVID-19 due to Omicron variant in Hong Kong

Abstract

Background: No nosocomial infection was recorded in our healthcare workers (HCWs) during the early phase of the coronavirus disease 2019 (COVID-19) pandemic. With the emergence of the Omicron variant of increased transmissibility, infection in HCWs occurred as expected. We aimed to study the epidemiology of infection in HCWs and to describe the infection control measures during the outbreak of the Omicron variant.

Methods: With daily rapid antigen testing and molecular confirmation test for COVID-19, infected HCWs were interviewed by infection control nurses (ICNs) to investigate the potential source of infection. The epidemiology of COVID-19 in Hong Kong served as reference.

Results: During the fifth wave of COVID-19 (31 December 2021 to 31 May 2022), 1,200,068 cases were reported (incidence 95 times higher than in preceding waves in Hong Kong; 162,103 vs 1,707 per million population respectively, P<0.001). The proportion of infected HCWs was significantly higher than that of the general population (24.9%, 1,607/6,452 vs 16.2%, 1,200,068/7,403,100 respectively; P<0.01). The proportion of infected non-clinical staff was significantly higher than that of clinical staff (31.8%, 536/1,687 vs 22.5%, 1,071/4,765 respectively; P<0.001). Of 82.8% (1,330/1,607) infected HCWs interviewed by ICNs, 99.5% (1,324/1,330) had been fully vaccinated; 49.5% (659/1,330) had no identifiable source; 40.7% (541/1,330) were probably infected from household members; 9.8% (130/1,330) had possible exposure to confirmed patients or HCWs, but no lapse in infection control measures or inappropriate use of personal protective equipment was recalled.

Conclusion: Omicron variant is highly transmissible such that breakthrough infection occurred despite high level of vaccination.

Keywords: COVID-19; Healthcare workers; Hong Kong; Omicron; SARS-CoV-2; Vaccination.

Figure 1

Epidemic curve of COVID-19 during the fifth wave in Hong Kong (31 December 2021 to 31 May 2022). Note. CTF in AWE, community treatment facility of around 1,000 beds in Asia World-Expo which was re-opened on 2 January 2022; FC, fangcang shelter for the purpose of community isolation facility. FC1 denotes fangcang shelter located in Tsing Yi which was opened on 1 March 2022; FC2 denotes fangcang shelter located in San Tin which was opened on 9 March 2022; FC3 denotes fangcang shelter located in Hong Kong-Zhuhai-Macao Bridge which was opened on 12 March 2022; FC4 denotes fangcang shelter located in Fanling which was opened on 13 March 2022; FC5 denotes fangcang shelter located in Hung Shui Kiu which was opened on 17 March 2022; FC6 denotes fangcang shelter located in Tam Mi which was opened on 24 March 2022. All six fangcang shelters were purposely built as community isolation facilities to provide a total of 20,000 beds; KTCT denotes Kai Tak cruise terminal which was converted into community isolation facility and opened on 21 March 2022 to provide around 1,000 beds; PRB denotes public rental buildings, Queens Hill Estate, located in Fanling, and Heng King House of Lai King Estate, located in Kwai Chung, which were converted into community isolation facility and opened on 24 February 2022 to provide around 3,000 residential flats; RAT, rapid antigen test; RT-PCR, reverse transcription polymerase chain reaction.

Figure 2

Number of COVID-19 cases in Queen Mary Hospital and Hong Kong West Cluster during the fifth wave of COVID-19. Note. HKWC, Hong Kong West Cluster; QMH, Queen Mary Hospital. Hong Kong West Cluster is a healthcare network comprising Queen Mary Hospital, a 1,700-bed university-affiliated tertiary referral center, and another 5 extended-care hospitals with a total of 1,700 beds. During the fifth wave of COVID-19, four out of 5 extended-care hospitals received clinically stable COVID-19 from Queen Mary Hospital.

Figure 3

Number of healthcare workers in Queen Mary Hospital infected with COVID-19. Note. The peak of healthcare worker infection occurred earlier than the peak of COVID-19 cases in the community and the hospital. It was the result of effort of infection control nurses to remind healthcare workers to avoid social gathering and obey social distancing when there was increasing HCW infection.

Figure 4

Analysis of COVID-19 infected healthcare workers in Queen Mary Hospital (31 December 2021 to 31 May 2022). Non-clinical staff includes administrative, clerical, and non-care related supporting staff. AGP, aerosol generating procedures; PPE, personal protective equipment.