How can we define early COVID-19 reinfections?
In a recent study published in the Emerging Infectious Diseases journal, researchers investigated coronavirus disease 2019 (COVID-19) reinfections.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfections are defined as either a positive polymerase chain reaction (PCR) test or a rapid antigen test detected 60 days after the detection of the previous positive PCR or rapid antigen test. However, emerging reports show that SARS-CoV-2 Omicron BA.1 variant reinfections could occur within 60 days of diagnosis with the Delta variant. Furthermore, studies have also revealed that Omicron BA.2 reinfections were reported 60 days after Omicron BA.1 diagnosis in young, unvaccinated individuals. Therefore, reinfection should be redefined since it subsequently affects retesting policies.
About the study
In the present study, researchers assessed the case definition of COVID-19 reinfections and their impact on retesting policies.
The team reported a case involving an immunocompetent 10-year-old child who had no notable medical history and was unvaccinated against COVID-19. The patient tested PCR positive for the SARS-CoV-2 Delta variant on 3 December 2021. The patient’s mother and brother also tested positive for COVID-19 but were both vaccinated. All three patients displayed mild COVID-19 symptoms.
Due to a sports-related injury, the child was hospitalized for surgery on 1 January 2022. COVID-19 screening performed before the surgery revealed that the patient was positive for SARS-CoV-2 infection with the Omicron BA.1 variant. The team noted that the BA.1 reinfection was diagnosed only 39 days after the previous Delta diagnosis. The patient was pauci-symptomatic throughout the course of the reinfection. Screening the patient’s brother for infection revealed a low viral load while the mother was COVID-19 negative.
To investigate this clinical case with respect to a wider epidemiological perspective, the team evaluated the incidence of early Omicron BA.1 reinfection after a history of Delta infection and Omicron BA.2 reinfection after BA.1 infection within a community setting. The team compared the vaccination status and age of the 96 patients who reported early reinfection with the vaccination rates reported for the corresponding age groups within the same geographical area.
Between 1 December 2021 and 7 February 2022, the team noted that the SARS-CoV-2 Delta variant infections were replaced by Omicron BA.1 infections as almost 59,515 patients tested COVID-19 positive. Among these patients, 0.15% had the SARS-CoV-2 spike (S) gene in their first sample detected using a PCR test that suggested the presence of the Delta variant in the sample. However, S-gene target failure (SGTF) was detected in the second COVID-19 positive sample collected during the period, which indicated an Omicron BA.1 reinfection shortly after Delta infection.
Similarly, the period between 1 January and 10 March 2022 was characterized by the replacement of the Omicron BA.1 variant by the BA.2 variant. In this period, almost 58,166 patients tested positive for COVID-19. Among these, 0.01% of the first samples collected showed SGTF while an S gene was found in the second positive sample. This indicated BA.2 reinfection after the diagnosis of BA.1 infection.
The team observed that in comparison to the age groups among the general population, patients who reported early reinfections were more likely to be either vaccinated, partially unvaccinated, or vaccinated but not boosted. Additionally, the median duration between the detection of two positive samples infected with distinct variants was 47 days.
The data collected by the team revealed that Omicron BA.1 reinfection diagnosed less than 60 days after a previous Delta variant infection and Omicron BA.2 reinfection detected after BA.1 infection can occur among young and unvaccinated individuals. Among the older patient groups, individuals who were unvaccinated or received either basic vaccination but no booster doses were more susceptible to reinfections as compared to patients who were vaccinated with their first booster dose. The team also observed that reinfections generally present mild disease symptoms and do not necessitate hospital admission.
Overall, the study showed that full viral replacement will continue to impact the duration as well as the efficacy of vaccination and immune responses. Hence, retesting of patients having a history of SARS-CoV-2 infection during conditions of sustained variant circulation is limited. However, in cases of antigenic drift resulting in a switch in predominant variants, the minimum testing interval should not be considered for the timely detection of COVID-19 reinfections.