Large-scale frequent testing and tracing to supplement control of Covid-19 and vaccination rollout constrained by supply.

Non-pharmaceutical interventions (NPI) were implemented all around the world in the fight against COVID-19: Social distancing, shelter-in-place, mask wearing, etc. to mitigate transmission, together with testing and contact-tracing to identify, isolate and treat the infected. The majority of countries have relied on the former measures, followed by a ramping up of their testing and tracing capabilities. We present here the cases of South Korea, Italy, Canada and the United States, as a look back to lessons that can be drawn for controlling the pandemic, specifically through the means of testing and tracing. By fitting a disease transmission model to daily case report data in each of the four countries, we first show that their combination of social-distancing and testing/tracing to date have had a significant impact on the evolution of their first wave of pandemic curves. We then consider the hypothetical scenario where the only NPI measures implemented past the first pandemic wave, consisted of isolating individuals due to repeated, country-scale testing and contact tracing, as a mean of lifting social distancing measures, without a resurgence of COVID-19. We give estimates on the average isolation rates needed to occur in each country. We find that testing and tracing each individual of a country, on average, every 4.5 days (South Korea), 5.7 days (Canada), 6 days (Italy) and 3.5 days (US), would have been sufficient to mitigate their second pandemic waves. We further show that to control infection resurgence during their second wave (Fall 2020), the countries would have needed higher rates, and we give explicit estimates for these new rates. We also considered a situation in Canada to see how a frequent large-scale asymptomatic testing and contact tracing can be used in combination with vaccination rollout to reduce the infection in the population. This offers an alternative approach towards preventing and controlling an outbreak when vaccine supply is limited, while testing capacity has been increasingly enhanced.