Can the transmission of the SARS-CoV-2 coronavirus be stopped without total containment via mini-containment cycles?
Text updated on 2020-07-13
To avoid total confinement, one strategy would be to go out, work and socialize for 4 days and then confine and telework for 10 days. This strategy is based on the fact that the peak of contagion for most patients begins 3-4 days after being infected and lasts 4-5 days. Researchers have evaluated this strategy and conclude that it is as effective as total containment in minimizing the risk of contagion.
To limit the spread of the COVID-19 epidemic, most countries have implemented containment periods, forcing the population to stay in their homes or in a specific place. The containment strategy limited the spread of the coronavirus by reducing the average reproduction rate (R) of CoV-2-SARS, i.e., the average number of people infected by a person carrying the coronavirus. When the R drops below 1, it means that on average one contagious person infects less than one person, thus gradually eliminating the epidemic.
Confinement cannot last more than a few months for psychological and socio-economic reasons. After the end of containment, outbreaks of contamination may reappear and the R-value may increase in some areas. Today, our knowledge of the disease makes it COVID-19 possible to consider alternative solutions to reduce the transmission of the SARS-CoV-2 coronavirus without going through total containment.
The particularity of the SARS-CoV-2 coronavirus is that it is contagious before the onset of symptoms of COVID-19. Based on the temporal characteristics of the incubation and contagion period, mini-containment cycles can be proposed: 4 days without containment then 10 days of containment which will limit the possibility of one person infecting others.
The "4 days out - 10 days in" cycles prevent people infected during the 4 days without containment from spreading the disease since they are confined during the days of their contagious period.
One study estimates that this "4 days out - 10 days in" strategy is as effective as total confinement: by reducing the number of contacts between people by 70%, the reproduction rate R falls below 1. This study did not analyse the effect of shorter confinement cycles.
One advantage of this approach is to safeguard 40% of the economy, but also to continue to have a social life and to avoid the cognitive and psychological problems induced by isolation in total confinement. The implementation of alternating teams in professional environments - with two teams performing their 4 days work over alternating weeks - allows for continuity in economic activity, without diminishing the effectiveness of the strategy.
This containment strategy is based on the results of a multi-parameter-dependent model with the following assumptions:
- A latency period (time between the moment of contamination and the beginning of the contagious period) of 3 days, which is consistent with the current data. See the question How long is a person contagious?.
- a peak of contagiousness that begins approximately 3 days after exposure to coronavirus and lasts 3-5 days, which is consistent with the current data. See the question How long is a person contagious?.
- a reproduction rate, R, of less than 3 during work periods, which seems correct given that the average R at the beginning of the epidemic before the implementation of the barrier measures was, on average, 3
- a decrease of at least 80% in the probability of contagion during periods of containment, which seems to be in line with current data
- an incubation period (time between contamination and the onset of symptoms) of less than 10 days, which is the case for 90% of patients
Total containment can have serious long-term economic, social, and psychological consequences. In order to continue to fight effectively against the spread of the disease, the strategy of alternating cycles of 4 days outside and 10 days confined is a promising alternative. Even if this strategy is not implemented on a large scale, applying it on an individual basis is effective since it at least reduces one's own probability of infecting others. Of course, do not do this if you are vulnerable, as this strategy does not protect you from contamination: remain vigilant!
Model estimating epidemic growth according to different applications of the "4 days out and 10 days confined" strategy. The number of contacts between people is reduced by 70%, allowing to maintain a reproduction rate, R, lower than 1.Karin, O., Bar-On, Y. M., Milo, T., Katzir, I., Mayo, A., Korem, Y., ... & Milo, R. (2020). Adaptive cyclic exit strategies from lockdown to suppress COVID-19 and allow economic activity. medRxiv.
The contagion begins 2.3 days before the onset of symptoms, which themselves begin 5 days after infection on average, giving a latency period of 2.7 days.He, X., Lau, E. H., Wu, P., Deng, X., Wang, J., Hao, X., ... & Mo, X. (2020). Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature medicine, 26(5), 672-675.
One model estimates a latency period of 3.7 days for SARS-CoV-2 coronavirus infection.Li, R., Pei, S., Chen, B., Song, Y., Zhang, T., Yang, W., & Shaman, J. (2020). Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV-2). Science, 368(6490), 489-493.
It has been observed that patients begin to isolate on average 2.9 days after the onset of the first symptoms. Although patients remain contagious when they are isolated, they do not infect anyone else. Therefore, it is estimated that the contagious period from the time they become contagious is about 2 average days of pre-symptomatic contagion until they are isolated and then 2.9 days after the onset of symptoms, making a total contagious period of 4.9 days.Liu, T., Hu, J., Kang, M., Lin, L., Zhong, H., Xiao, J., ... & Deng, A. (2020). Transmission dynamics of 2019 novel coronavirus (2019-nCoV).
In this study, it was observed that patients begin to isolate themselves on average 4.6 days after the onset of the first symptoms, a period where they are 6.6 days at risk of infecting someone by adding the average 2 days of pre-symptomatic contagion.Bi, Q., Wu, Y., Mei, S., Ye, C., Zou, X., Zhang, Z., ... & Gao, W. (2020). Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study. The Lancet Infectious Diseases.
Modelling analysis shows that a "4 days out and 8 days confined" strategy is effective in stopping the spread of the SARS-CoV-2 epidemic.Cornes, F. E., Frank, G. A., & Dorso, C. O. (2020). Cyclical lock-down and the economic activity along the pandemic of COVID-19. arXiv preprint arXiv:2006.06409.
A meta-analysis (13 studies in China) estimates R0 between 2.8 (median) and 3.3 (mean).Liu, Y., Gayle, A. A., Wilder-Smith, A., Rocklev, J. (2020). The reproductive number of COVID-19 is higher compared to SARS coronavirus. Journal of travel medicine.
An analysis of contacts between people is compatible with a decrease in the contagion and R by 85-90% after confinement.Zhang, J., Litvinova, M., Liang, Y., Wang, Y., Wang, W., Zhao, S., ... & Ajelli, M. (2020). Changes in contact patterns shape the dynamics of the COVID-19 outbreak in China. Science.
An econometric analysis estimates that containment policies reduce the contagion rate (R) by 82%.Hsiang, S., Allen, D., Annan-Phan, S., Bell, K., Bolliger, I., Chong, T., ... & Lau, P. (2020). The effect of large-scale anti-contagion policies on the COVID-19 pandemic. Nature, 1-9.
Based on 181 cases in China, it is observed that in 90% of cases the onset of symptoms occurs within 10 days of infection. After the onset of symptoms, patients can theoretically isolate themselves to avoid infecting others.Lauer, S. A., Grantz, K. H., Bi, Q., Jones, F. K., Zheng, Q., Meredith, H. R., ... & Lessler, J. (2020). The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: estimation and application. Annals of internal medicine, 172(9), 577-582.