Effect of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) mRNA vaccination in healthcare workers with high-risk coronavirus disease 2019 (COVID-19) exposure.

Healthcare providers (HCPs) have experienced significant burden of disease throughout the coronavirus disease 2019 (COVID-19) pandemic.[1,2] Infection prevention measures mitigated the significant initial work-related risk; however, many HCPs developed COVID-19 following exposure to severe acute respiratory coronavirus virus 2 (SARS-CoV-2)–infected individuals at home or in the community.[2,3] Healthcare systems have developed policies around SARS-CoV-2 testing, returning to work after infection, and high-risk exposures for their employees.[4] At Nebraska Medicine, employees were asked to report any COVID-19 symptoms or exposures to the Employee Health Department for instructions on testing, quarantine, and isolation. Due to the implementation of comprehensive hospital-based COVID-19 infection control policies and procedures, the major risk factor for employee quarantine at our institution was household contact with an infected family member. The emergency use authorization of 2 messenger RNA (mRNA) vaccines—the BNT162b2 vaccine (Pfizer-BioNTech) and the mRNA-1273 vaccine (Moderna)—were critical events in the response to the pandemic.[5,6] In clinical trials, both vaccines were shown to be very effective at preventing severe disease and hospitalization due to COVID-19; however, information regarding acquisition of infection with subsequent asymptomatic shedding of SARS-CoV-2 remain limited, particularly following known exposures to close contacts with COVID-19 cases.[5,6] Therefore, we describe the incidence of SARS CoV-2 infection among vaccinated employees at our institution after a high-risk household exposure to a family member with COVID-19.

Since December 18, 2020, Nebraska Medicine, a tertiary-care academic medical center in Omaha, Nebraska, has fully vaccinated 12,160 employees with 1 of the 2 available mRNA vaccines. The availability of effective vaccines required adjustment of the return-to-work procedure after COVID-19 exposures. Employees with a household exposure to a close contact with active COVID-19 infection and who were deemed essential and unable to work remotely were eligible to enroll in a screening program rather than completing a home quarantine period. Employees were eligible for the screening program if their exposure was >7 days after the second dose of SARS-CoV-2 vaccine and they remained asymptomatic. If these criteria were met, the employees underwent a nasopharyngeal swab (NP) for SARS-CoV-2 testing by PCR, and, if negative, they were allowed to return to work. The employee was then tested serially by NP swab every 5–7 days until at least 7 days from their last exposure to the SARS-CoV-2–positive household member during the period of viral shedding (typically 10 days). Employees were instructed to self-isolate from the positive individual in the home, if logistically feasible. Employees unable to do so were not excluded from the serial testing program, but their period of serial testing was extended until 7 days after the household contact was considered noninfectious.

As of March 30, 2021, 48 employees had been enrolled in the protocol. Of these, 5 were still actively undergoing serial testing, and 43 completed the protocol. Among them, 38 did not develop symptoms and were negative for SARS-CoV-2 on entry into protocol and on serial testing. Also, 13 employees had 1 test. Furthermore, 11 were able to physically distance away from the positive contact; 23 had 2 negative tests; and 2 had 3 or more negative tests. Moreover, 5 employees tested positive: 3 employees were positive in the protocol and 2 were positive on entry testing. These data currently represent a vaccine failure rate of 11.6% (5 of 43). We were not able to determine whether physical distancing in the household had any impact on transmission.

Of the 5 fully vaccinated employees who tested positive, all had asymptomatic or mild disease. None developed severe disease requiring hospitalization, which is consistent with previously published data about infections in individuals vaccinated with SARS-CoV-2 mRNA vaccines.[5,6] However, 3 developed mild symptoms with cough, fever, congestion, or headache, and 2 were asymptomatic (Table 1). None of the employees who tested positive were immunocompromised. They ranged in age from 23 to 29 years. The timing of the positive result did not show a trend. Furthermore, 2 employees tested positive at initiation of the protocol: 1 was asymptomatic and 1 with mild symptoms. Of the remaining 3 employees, 2 developed symptoms and tested positive on the second test. The last employee remained asymptomatic and tested positive on the final test in the protocol.

Table 1.

SARS-CoV-2–Positive Employees

Household Exposure	Symptoms	Ct Value[a]	Date of HH Symptom Start	Date of Employee Positive Test
Partner	Fever, cough	30	3/7/2021	3/9/2021
Partner	None	38	2/21/2021	3/10/2021
Partner	Congestion	26	3/24/2021	3/29/2021
Partner	None	37	3/11/2021	3/13/2021
Partner	Congestion, headache	21	3/19/2021	3/20/2021

Note. Ct, cycle threshold.

Ct values obtained on the Roche Cobas 6800 system using the SARS-CoV-2 and influenza A&B assays.

The cycle threshold (Ct) values for the asymptomatic individuals were 37 and 38, and the Ct values were 21, 26, and 30 for the symptomatic employees (Table 1). These relatively high Ct values are consistent with reports that viral loads, as measured by Ct values, are lower >12 days after mRNA vaccination compared to nonvaccinated individuals.[7]

All 5 vaccinated employees who tested positive had a domestic partner as the positive household contact. None of employees who were exposed to a positive child or nonsignificant other adult became infected. Spousal relationship has previously been shown to be a high risk for secondary infection, with a mean household secondary attack rate of spouses of 37.8% in prevaccination data.[8] In our limited sample, the rate of secondary infection in vaccinated healthcare workers when exposed to a SARS-CoV-2–positive partner was 22.7%, which represents a significant risk of infection.

Although our study had a small sample size, the data demonstrate a persistent risk of acquisition of infection following exposure to a household member, particularly a partner with COVID-19. None of the vaccinated employees developed severe disease, which is encouraging but could also be due to risk profile. Further research into COVID-19 after vaccination is needed, including the likelihood of transmission by fully vaccinated, asymptomatic individuals in different settings.