Compliance with testing was high, with 80% of DCT participants submitting at least one LFD result. Attack rates among contacts of DCT participants who had received two vaccine doses (>14 days before recruitment) also showed non-inferiority compared with self-isolation-participants, suggesting that DCT would be of value among fully vaccinated people. Consistent with this finding, the number of observed tertiary cases per secondary case was 0♱4 in the DCT group and 0♱6 in the self-isolation group. By ascertaining the proportion of contacts of PCR-positive study participants who became tertiary cases in each group, we showed that daily contact testing (DCT) was a safe alternative to self-isolation regarding onward transmission of SARS-CoV-2, with a difference in attack rates of –1♲% among contacts of secondary cases, indicating non-inferiority of DCT. To our knowledge, we present the first randomised controlled trial in a general population of close contacts of COVID-19 cases to assess whether daily LFDs with 24 h exemption from self-isolation for essential activities following each negative LFD result is a safe alternative to self-isolation. Data collection is complete analysis is ongoing. This study is registered with the Research Registry (number 6809). The primary analysis was a modified intention-to-treat analysis excluding those who actively withdrew from the study as data from these participants were no longer held. Attack rates were adjusted for household exposure, vaccination status, and ability to work from home.
Attack rates were derived from Bernoulli regression models using Huber-White (robust) sandwich estimator clustered standard errors. The primary outcome of the study was the attack rate, the percentage of secondary contacts (close contacts of SARS-CoV-2-positive study participants) who became COVID-19 cases (tertiary cases) in each group. Participants were prospectively followed up, with the effect of each intervention on onward transmission established from routinely collected NHS Test and Trace contact tracing data for participants who tested PCR-positive for SARS-CoV-2 during the study period and tertiary cases arising from their contacts (ie, secondary contacts). Consenting participants were randomly assigned to self-isolation (single PCR test, 10-day isolation) or daily contact testing (DCT seven LFD tests, two PCR tests, no isolation if negative on LFD) participants from a single household were assigned to the same group. We conducted a randomised, controlled, non-inferiority trial in adult contacts identified by COVID-19 contact tracing in England. The Lancet Regional Health – Western Pacific.The Lancet Regional Health – Southeast Asia.The Lancet Gastroenterology & Hepatology.
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