Daily Rapid Antigen Exit Testing to Tailor University COVID-19 Isolation Policy

A robust web-based tool to predict viral shedding in patients with Omicron SARS-CoV-2 variants

Background

Data on viral kinetics and variants affecting the duration of viral shedding were limited. Our objective was to determine viral shedding in distinct severe acute respiratory syndrome coronavirus 2 variants, including Omicron BA.4/5 and BF.7, and to identify the relevant influencing factors.

Methods

We carried out a longitudinal cohort study at Beijing Xiaotangshan Fangcang shelter hospital from May to June 2022 (Omicron BA.4/5) and from November to December 2022 (Omicron BF.7). Nucleocapsid protein (N) and open reading frame (ORF) genes were considered as the target genes of the reverse transcription PCR. The daily results of cycle threshold (CT), including lowest ORF1ab-CT values for days 1-3 post-hospitalisation and lowest N-CT values for days 1-3 post-hospitalisation (CT3minN) and demographic and clinical characteristics were collected.

Results

1433 patients with coronavirus disease 2019 (COVID-19) were recruited from the Fangcang shelter hospital, in which 278 patients were diagnosed with Omicron BA.4/5 and 1155 patients with Omicron BF.7. Patients with BF.7 infection showed a longer duration of viral shedding. The duration of viral shedding was associated with the variants age, alcohol use, the severity of COVID-19 and CT3minN. Moreover, the nomogram had excellent accuracy in predicting viral shedding.

Conclusions

Our results indicated that patients with Omicron BF.7 had a longer period of contagiousness than those with BA.4/5. The duration of viral shedding was affected by a variety of factors and the nomogram may become an applicable clinical instrument to predict viral shedding. Furthermore, we developed a new COVID-19 viral shedding predicting model that can accurately predict the duration of viral shedding for COVID-19, and created a user-friendly website to apply this prediction model (https://puh3.shinyapps.io/CVSP_Model/).

A test-based strategy for early return to work for health-care workers with COVID-19 during the Omicron wave, Brunei Darussalam, 2022

Objective

This paper summarizes and evaluates a test-based strategy for early return to work for health-care workers (HCWs) with mild coronavirus disease in Brunei Darussalam during the Omicron wave in February 2022 and compares the characteristics of HCWs by how long it took them to return to work.

Methods

The early return-to-work strategy involved testing on day 3 of infection with reverse transcription-polymerase chain reaction and with a rapid antigen test on days 5 and 6 or days 5 and 7. Data about infected HCWs were extracted from the Ministry of Health's public health surveillance database. Percentages and proportions were used for descriptive statistics, and Pearson's χ2 test and the paired t-test were used to compare return-to-work patterns with demographic factors and vaccination status of the HCWs, as well as between cycle threshold (Ct) values and occupational groups of HCWs.

Results

From 15 February to 15 March 2022, a total of 1121 HCWs were notified as being infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Of these, 175 (15.6%) were able to return to work on day 4 of their infection, 153 (13.6%) on day 6 and 268 (23.9%) on day 7; 525 (46.8%) required 10 days of home isolation. Statistically significant associations were observed between return-to-work periods and occupational group (P < 0.01) and Ct value (P < 0.01), but not between return to work and age, sex or vaccination status.

Discussion

This test-based strategy ensured a balance between mitigating a shortage of HCWs and enabling them to return to work early without compromising their safety and that of their patients.

Comparing SARS-CoV-2 testing positivity rates and COVID-19 impact among different isolation strategies: a rapid systematic review and a modelling study

Background

The optimal isolation duration for patients with COVID-19 remains unclear. To support an update of World Health Organization (WHO)'s Living Clinical management guidelines for COVID-19 (https://www.who.int/publications/i/item/WHO-2019-nCoV-clinical-2022.2), this rapid systematic review and modelling study addresses the effects of different isolation periods for preventing onward transmission leading to hospitalisation and death among secondary cases.

Methods

We searched the WHO COVID-19 database for studies up to Feb 27, 2023. We included clinical studies of any design with COVID-19 patients confirmed by PCR test or rapid antigen test addressing the impact of any isolation strategy on preventing the spread of COVID-19. There were no restrictions on publication language, publication status, age of patients, severity of COVID-19, variants of SARS-COV-2, comorbidity of patients, isolation location, or co-interventions. We performed random-effects meta-analyses to summarise testing rates of persistent test positivity rates after COVID-19 infection. We performed pre-specified subgroup analyses by symptom status and meta-regression analyses for the proportion of fully vaccinated patients. We developed a model to compare the effects of three isolation strategies on onward transmission leading to hospitalisation and death. The three isolation strategies were (1) 5-day isolation, with no test to release; (2) removal of isolation based on a negative test; and (3) 10-day isolation, with no test to release. The model incorporates estimates of test positivity rates, effective reproduction number, isolation adherence, false negative rate, and hospitalisation rates or case fatality rates. To assess the impact of varying isolation adherence and false negative rates on rapid antigen testing, we conducted some sensitivity analyses. We used the Grading of Recommendations Assessment, Development and Evaluation approach to assess certainty of evidence. The protocol is registered with PROSPERO (CRD42022348626).

Findings

Fifteen studies addressing persistent test positivity rates including 4188 patients proved eligible. Asymptomatic patients (27.1%, 95% CI: 15.8%-40.0%) had a significantly lower rapid antigen test positive rate than symptomatic patients (68.1%, 95% CI: 40.6%-90.3%) on day 5. The rapid antigen test positive rate was 21.5% (95% CI: 0-64.1%; moderate certainty) on day 10. Our modelling study suggested that the risk difference (RD) for asymptomatic patients between 5-day isolation and 10-day isolation in hospitalisations (23 more hospitalisations of secondary cases per 10,000 patients isolated, 95% uncertainty interval (UI) 14 more to 33 more) and mortality (5 more per 10,000 patients, 95% UI 1 to 9 more) of secondary cases proved very small (very low certainty). For symptomatic patients, the potential impact of 5- versus 10-day isolation was much greater in hospitalisations (RD 186 more per 10,000 patients, 95% UI 113 more to 276 more; very low certainty) and mortality (RD 41 more per 10,000 patients, 95% UI 11 more to 73 more; very low certainty). There may be little or no difference between removing isolation based on a negative antigen test and 10-day isolation in the onward transmission leading to hospitalisation or death, but the average isolation period (mean difference -3 days) will be shorter for the removal of isolation based on a negative antigen test (moderate certainty).

Interpretation

5 days versus 10 days of isolation in asymptomatic patients may result in a small amount of onward transmission and negligible hospitalisation and mortality; however, in symptomatic patients, the level of onward transmission is concerning and may lead to high hospitalisation and death rates. The evidence is, however, very uncertain.

Funding

This work was done in collaboration with WHO.

Quantifying the impact of immune history and variant on SARS-CoV-2 viral kinetics and infection rebound: A retrospective cohort study

Background

The combined impact of immunity and SARS-CoV-2 variants on viral kinetics during infections has been unclear.

Methods

We characterized 1,280 infections from the National Basketball Association occupational health cohort identified between June 2020 and January 2022 using serial RT-qPCR testing. Logistic regression and semi-mechanistic viral RNA kinetics models were used to quantify the effect of age, variant, symptom status, infection history, vaccination status and antibody titer to the founder SARS-CoV-2 strain on the duration of potential infectiousness and overall viral kinetics. The frequency of viral rebounds was quantified under multiple cycle threshold (Ct) value-based definitions.

Results

Among individuals detected partway through their infection, 51.0% (95% credible interval [CrI]: 48.3-53.6%) remained potentially infectious (Ct <30) 5 days post detection, with small differences across variants and vaccination status. Only seven viral rebounds (0.7%; N=999) were observed, with rebound defined as 3+days with Ct <30 following an initial clearance of 3+days with Ct ≥30. High antibody titers against the founder SARS-CoV-2 strain predicted lower peak viral loads and shorter durations of infection. Among Omicron BA.1 infections, boosted individuals had lower pre-booster antibody titers and longer clearance times than non-boosted individuals.

Conclusions

SARS-CoV-2 viral kinetics are partly determined by immunity and variant but dominated by individual-level variation. Since booster vaccination protects against infection, longer clearance times for BA.1-infected, boosted individuals may reflect a less effective immune response, more common in older individuals, that increases infection risk and reduces viral RNA clearance rate. The shifting landscape of viral kinetics underscores the need for continued monitoring to optimize isolation policies and to contextualize the health impacts of therapeutics and vaccines.

Funding

Supported in part by CDC contract #200-2016-91779, a sponsored research agreement to Yale University from the National Basketball Association contract #21-003529, and the National Basketball Players Association.