Postvaccination COVID-19 among Healthcare Workers, Israel

Coronavirus disease (COVID-19) symptoms can be mistaken for vaccine-related side effects during initial days after immunization. Among 4,081 vaccinated healthcare workers in Israel, 22 (0.54%) developed COVID-19 from 1–10 days (median 3.5 days) after immunization. Clinicians should not dismiss postvaccination symptoms as vaccine-related and should promptly test for COVID-19.


DISPATCHES
L arge-scale vaccination of risk groups and later the general population is the single most effective public health measure for mitigation of the coronavirus disease (COVID-19) pandemic. National COVID-19 vaccination programs started during December 2020 in several countries and prioritized healthcare workers (HCWs) (1). In some countries the vaccination programs coincided with a surge in detected COVID-19 cases and increased burden on the healthcare system (2).
Sheba Medical Center is a large hospital with 9,069 staff members in Ramat-Gan, Israel. The hospital started its personnel vaccination program on December 20, 2020, and excluded workers who had recovered from COVID-19. During the fi rst week of the campaign, 4,081 (45%) eligible staff members received the fi rst dose of BNT162b2. Concurrently, the national COVID-19 positivity rate rapidly increased to >6% on January 3, 2021 (2).

The Study
The hospital's Infection Prevention and Control Unit conducted active and passive surveillance of vaccinated staff by using daily health questionnaires, hotlines, on-call infectious disease unit staff, and post-vacci-nation web-based questionnaires to identify and test symptomatic HCWs. Among 4,081 HCWs vaccinated in the fi rst week of the campaign, 22 (0.54%) later had laboratory-confi rmed COVID-19 (Table). The average age among COVID-19-positive vaccinated HCWs was 45.3 years (±9.85 years), and they belonged to different healthcare sectors and worked on various wards.
Among the 22 vaccinated HCWs who tested positive for COVID-19, 13 were tested because they had symptoms, most commonly an infl uenza-like illness that included fever, chills, cough, headache, myalgia, and sore throat. Two vaccinated HCWs were tested because of exposure to confi rmed or suspected COV-ID-19 cases yet reported symptoms upon questioning. Asymptomatic COVID-19 cases were identifi ed among HCWs as part of postexposure screening. Among the 22 COVID-19-positive HCWs, 11 had presumable community-related exposures, 4 of whom reported exposure incidents that occurred before or on the date of vaccination. An investigation conducted by the hospital's Infection Control and Prevention Unit identifi ed 10 healthcare-related secondary exposures. However, we did not identify any point-source exposures or CO-VID-19 clusters linked to the immunization process.
Among the 11 vaccinated HCWs who reported COVID-19 symptoms, the median time between the fi rst dose of BNT162b2 immunization and symptom onset was 3.5 (range 0-10) days; we excluded 1 vaccinee from our calculation and analysis because the HCW had symptoms before immunization (Table). The median time between the onset of symptoms and testing was 1 day, demonstrating the high level of suspicion for COVID-19 during the vaccination campaign.
Of note, apart from the need for early detection, persons who test positive for COVID-19 after receiving the fi rst vaccine dose (whether asymptomatic and tested following exposure or tested because they are symptomatic) are not eligible to receive the second dose, according to Ministry of Health policy. However, depending on availability of vaccines, this policy might change when further data are collected.

Conclusions
COVID-19 in HCWs is a major concern for health authorities worldwide. HCWs, especially acute and chronic care facility personnel, are at high risk for contracting symptomatic and asymptomatic COVID-19 and might become infected at home or nosocomially while caring for patients or interacting with other staff members (5)(6)(7). Infections among HCWs have an immediate effect on their close occupational environment and the overall healthcare system. Secondary exposures, isolation, and infections of staff can substantially impair the capacity of a single ward to care for patients, creating a snowball effect with collateral damage to both the functional resilience of the facility and morale of staff. Consequently, as soon as COVID-19 vaccines were deployed in Israel, HCWs were the first group to receive it.
We report 22 cases of early, postimmunization, laboratory-confirmed COVID-19 among HCWs during the launch of the vaccination campaign in a large hospital in Israel. BNT162b2 is not likely to exert protection against clinical disease during the first days after receipt of the first dose. Efficacy of the BNT162b was 52% a week after the first dose, and positive CO-VID-19 cases were described among vaccinees even early after the second dose (8). Thus, during a largescale immunization campaign coinciding with rapid national increase in COVID-19 cases, some immunized persons likely will develop clinical disease.
The co-occurrence of vaccination deployment with the rapidly climbing COVID-19 spread in many parts of the world is a confusing period in which hope is mixed with great vulnerability. The phenomenon of pandemic fatigue, in which the population tires of constant safety precautions, testing, isolation, and restrictions, could lead to less social distancing and personal protection. Pandemic fatigue coupled with the availability of a vaccine, might give the population a false sense of reassurance and consequently lead to a brisk increase in COVID-19 cases. Thus, almost every physical complaint after vaccination poses a true diagnostic dilemma as to whether an adverse reaction or a new COVID-19 infection is the cause. Undetected COVID-19 cases among HCWs could be hazardous for patients and other staff. Clinicians should have a high level of suspicion of reported symptoms and avoid dismissing complaints as vaccine-related until true infection is ruled out and vaccinees are tested. Active and passive surveillance that enables rapid testing and initiation of infection control measures are essential in preventing possible diagnostic delays and secondary exposures. Therefore, healthcare-related indications for testing should not be altered until systematic and exhaustive data are gathered regarding vaccine effectiveness in healthcare settings.

About the Author
Dr. Amit is a certified internist, infectious disease specialist, and clinical microbiologist, and is the director of the Clinical Microbiology Laboratory Department at Sheba Medical Center, Israel. Her fields of research include clinical microbiology and communicable diseases epidemiology.
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