Vaccination Alone Can’t Keep Health Care Workers Safe from COVID-19 Reinfection


Reinfections among study participants most likely occurred outside the hospital setting where workers might let their guard down and not practice nonpharmaceutical mitigation efforts against SARS-CoV-2.

Workers in health care settings need to continue with nonpharmaceutical COVID-19 mitigation efforts inside and outside of their place of employment and regardless of their vaccination status in order to better prevent reinfection. Vaccination nonetheless greatly reduces reinfection and ensures that vaccinated health care workers have milder symptoms and can return to work sooner, according to a recent study in Clinical Infectious Diseases (CID).

After monitoring 2425 fully vaccinated staff at two referral hospitals in Tokyo and comparing their data to that of a control group, investigators with Japan’s National Center for Global Health and Medicine (NCGM) stated that “vaccination programs alone cannot eliminate the risk of infection by the Delta variant. Still, we could reasonably infer that the program has contributed to the sizable reduction in the number of COVID-19 patients among the staff during the largest epidemic [up until that point].” NCGM comprises two hospitals that also serve as research centers on infectious disease.

Despite the effectiveness of the COVID-19 vaccines, the findings bolster the argument by some medical experts that we cannot vaccinate our way out of the COVID-19 pandemic. “NCGM has adopted comprehensive measures against nosocomial infection since the early phase of the epidemic,” the study states. “The current data confirm the significant role of these measures to protect health care workers against the Delta variant infection.”

The comprehensive nonpharmaceutical anti-COVID-19 measures adopted by NCGM include avoiding what the institution refers to as the 3Cs: crowded places, close-contact settings, and confined and enclosed spaces without wearing a mask. They also include social distancing, cough etiquette, not touching eyes, nose and mouth, and hand hygiene. The workers did a good job of following mitigation efforts inside the hospital but not so much outside of it. The study states “infection among the staff had occurred mainly outside the hospital (household, community, etc.).

NCGM gathered data in three surveys taken from July 2020 to October 2021. Data collected from hospital workers who participated in the third survey, conducted in June 2021 after an in-house vaccination program, were used as the basis for the case-control analysis.

The study states that in those surveys “we measured anti-SARS-CoV-2 nucleocapsid—(all surveys) and spike—(from the second survey onward) protein antibodies, stored serum samples at -80 °C, and collected COVID-19 related information (vaccination, occupational infection risk, infection prevention practices, etc.) via a questionnaire.”

Seventeen cases of COVID-19 were found among staff between November 2020 and February 2021 during the third wave of the pandemic and before the hospitals launched an in-house vaccination program. During Japan’s fourth wave, between April and May 2021, there were no cases of COVID-19 among staff. The fifth wave occurred between July and September 2021, and was fueled by the Delta variant. There were 23 cases, and of those cases, 22 of the hospital workers were fully vaccinated.

The study states that “the risk of infection during the two months in the fifth wave (after the in-house vaccination program) was only slightly higher than that observed during the third wave (December 2020 to January 2021) (before the program) (5.2 per 1000 persons), while the number of cases in Tokyo during the fifth wave (n=133,989) was 3.5 times higher than that during the third wave (n=38,492).”

Health care workers who completed at least a two-dose vaccination regimen showed mild or no symptoms and were able to return to work quickly. “These data support that vaccination contributes to the maintenance of hospital function by shortening sick leave due to COVID-19 of healthcare workers and facilitating their earlier return to work…,” the study states.

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