Log in to MyACC
SARS-CoV-2 Infections of Antibody-Positive vs. -Negative Health Care Workers
Quick Takes
- The SIREN (SARS-CoV-2 Immunity and Reinfection Evaluation) study is a large, national, multicenter prospective cohort study of hospital health care workers (in the UK, which investigated whether the presence of antibodies against SARS-CoV-2 was associated with a reduction in the subsequent risk of symptomatic and asymptomatic reinfection over the 12 months of follow-up.
- A previous history of SARS-CoV-2 infection was associated with an 84% lower risk of infection, with median protective effect observed 7 months following primary infection.
- The B.1.1.7 variant did not appear to impact reinfection rates.
Study Questions:
How does the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection rate in health care workers with previous exposure to SARS-CoV-2 compare to the infection rate in nonexposed health care workers?
Methods:
The SIREN (SARS-CoV-2 Immunity and Reinfection Evaluation) study is a large, national, multicenter prospective cohort study of hospital health care workers (including administrative and support staff) across the National Health Service (NHS) in the United Kingdom (UK), which investigated whether the presence of antibodies against SARS-CoV-2 was associated with a reduction in the subsequent risk of symptomatic and asymptomatic reinfection over the 12 months of follow-up. At enrollment, participants were assigned to either the positive cohort (antibody positive, or previous positive polymerase chain reaction [PCR] or antibody test) or negative cohort (antibody negative, no previous positive PCR or antibody test). Questionnaires on symptoms and exposures were sent electronically at baseline and every 2 weeks. SARS-CoV-2 antibody and PCR testing were done at enrollment and regular intervals (2-4 weeks). The primary outcome was reinfection in the positive cohort or a primary infection in the negative cohort, determined by PCR tests. Seroconversions were excluded when not associated with a positive PCR test.
Results:
A total of 25,661 participants (84% women, 87% White, median age 46 years) with linked data on antibody and PCR testing and enrolled from June 2020–December 2020 were included in the analysis: 8,278 (32.3%) were assigned to the positive and 17,383 (67.7%) to the negative cohort. Over 90% of the positive cohort were antibody-positive at enrollment. The median follow-up time per participant was 275 days, with a median of eight post-enrollment PCR tests (interquartile range, 6–11) and five post-enrollment antibody tests (3–7) done during that time. A total of 1,859 new infections were detected: 1,704 in the negative cohort and 155 reinfections in the positive cohort. Most reinfected participants had antibodies at baseline (82%). The median interval between the primary infection and reinfection episode was approximately 200 days (range 90–345 days). Half of the reinfections were associated with symptoms. The incidence density was 7.6 reinfections per 100,000 person-days in the positive cohort, compared with 57.3 primary infections per 100,000 person-days in the negative cohort: an 84% lower risk of infection. There was no evidence of the B.1.1.7 variant impacting reinfection rates.
Conclusions:
A previous history of SARS-CoV-2 infection was associated with an 84% lower risk of infection, lasting for an average of 7 months following primary infection.
Perspective:
The perceived risk of reinfection from SARS-CoV-2 from media reports has led to significant anxiety in the population and amongst policy makers. This study provides crucial information on the duration of immunity after a SARS-CoV-2 infection, which will guide discussions on social distancing measures and recommendations and the timing of vaccination in that patient population. Essentially, the study confirms that a previous SARS-CoV-2 infection confers comparable if not better protection compared to vaccination (based on data from the ChAdOx1 trial). More than 90% of individuals infected with SARS-CoV-2 develop antibodies about 1 week after symptom onset, persisting for at least 3 months. The average time to reinfection in this preliminary report was 7 months, despite most patients reinfected having had a positive antibody at enrollment; confirming previous reports that immunity may last approximately 6 months. Overall, these findings are tremendously reassuring. It is possible that the duration of immunity from a previous infection lasts much longer, which we anticipate will be confirmed by the follow-up analysis of SIREN.
Clinical Topics: COVID-19 Hub, Prevention
Keywords: Administrative Personnel, Antibodies, Anxiety, Coronavirus, COVID-19, Health Personnel, Immunity, Polymerase Chain Reaction, Primary Prevention, SARS-CoV-2, Vaccination
< Back to Listings
