Quarantine time after contact with a confirmed COVID-19 case could potentially be reduced to seven days without raising the risk of onward transmission, according to research carried out by the Centre for the Mathematical Modelling of Infectious Diseases COVID-19 working group.
The modelling study, published today in the Lancet Public Health, aimed to assess the merit of testing contacts to avert onward transmission and to replace or reduce the length of quarantine for uninfected contacts.
The research compared the performance of quarantines of differing durations, testing with either PCR or lateral flow antigen (LFA) tests at the end of quarantine, and daily LFA testing without quarantine, against the current 14-day quarantine strategy.
Assuming moderate levels of adherence to quarantine and self-isolation, self-isolation alone can prevent 37 per cent (95% uncertainty interval [UI], 12%-56%) of onward transmission potential from secondary cases.
Fourteen-day post-exposure quarantine reduces transmission by 59 per cent (95% UI, 28%-79%), whereas quarantine with release after a negative PCR test seven days after exposure might avert a similar proportion (54%; 95% UI, 31%-81%; risk ratio [RR], 0.94; 95% UI, 0.62-1.24) to that of the 14-day period, as would quarantine with a negative LFA test seven days after exposure (50%; 95% UI, 28%-77%; RR, 0.88; 95% UI, 0.66-1.11) or daily testing without quarantine for five days after tracing (50%; 95% UI, 23%-81%; RR, 0.88; 95% UI, 0.60-1.43) if all tests are negative.
The study does not evaluate the number or cost of tests that would be required for this approach.
The authors say a stronger effect might be possible if individuals isolate more strictly after a positive test and if contacts can be notified faster.
Joint lead author, Assistant Professor Sam Clifford, from the London School of Hygiene & Tropical Medicine, said: “Our findings suggest that incorporating testing of contacts into a trace-isolate system could potentially help to reduce quarantine times, and this in turn may improve adherence by making it easier to complete the full isolation period."