  The quarantine of identified close contacts has been vital to reducing
transmission rates and averting secondary infection risk before symptom onset
and by asymptomatic cases. The effectiveness of this contact tracing strategy
to mitigate transmission is sensitive to the adherence to quarantines, which
may be lower for longer quarantine periods or in vaccinated populations (where
perceptions of risk are reduced). This study develops a simulation model to
evaluate contact tracing strategies based on the sequential testing of
identified contacts after exposure as an alternative to quarantines, in which
contacts are isolated only after confirmation by a positive test. The analysis
considers different number and types of tests (PCR and lateral flow antigen
tests (LFA)) to identify the cost-effective testing policies that minimize the
expected infecting days post-exposure considering different levels of testing
capacity. This analysis suggests that even a limited number of tests can be
effective at reducing secondary infection risk: two LFA tests (with optimal
timing) avert infectiousness at a level that is comparable to 14-day quarantine
with 80-90% adherence, or equivalently, 7-9 day quarantine with full adherence
(depending on the sensitivity of the LFA test). Adding a third test (PCR or
LFA) reaches the efficiency of a 14-day quarantine with 90-100% adherence.
These results are robust to the exposure dates of the contact, test sensitivity
of LFA and alternative models of viral load evolution, which suggests that
simple testing rules can be effective for improving contact tracing in settings
where strict quarantine adherence is difficult to implement.
