Downsizing of COVID-19 contact tracing in highly immune populations

Abstract

Contact tracing is a key component of successful management of COVID-19. Contacts of infected individuals are asked to quarantine, which can significantly slow down (or prevent) community spread. Contact tracing is particularly effective when infections are detected quickly, when contacts are traced with high probability, when the initial number of cases is low, and when social distancing and border restrictions are in place. However, the magnitude of the individual contribution of these factors in reducing epidemic spread and the impact of population immunity (due to either previous infection or vaccination), in determining contact tracing outputs is not fully understood. We present a delayed differential equation model to investigate how the immunity status and the relaxation of social distancing requirements affect contact tracing practices. We investigate how the minimal contact tracing efficiency required to keep an outbreak under control depends on the contact rate and on the proportion of immune individuals. Additionally, we consider how delays in outbreak detection and increased case importation rates affect the number of contacts to be traced daily. We show that in communities that have reached a certain immunity status, a lower contact tracing efficiency is required to avoid a major outbreak, and delayed outbreak detection and relaxation of border restrictions do not lead to a significantly higher risk of overwhelming contact tracing. We find that investing in testing programs, rather than increasing the contact tracing capacity, has a larger impact in determining whether an outbreak will be controllable. This is because early detection activates contact tracing, which will slow, and eventually reverse exponential growth, while the contact tracing capacity is a threshold that will easily become overwhelmed if exponential growth is not curbed. Finally, we evaluate quarantine effectiveness in relation to the immunity status of the population and for different viral variants. We show that quarantine effectiveness decreases with increasing proportion of immune individuals, and increases in the presence of more transmissible variants. These results suggest that a cost-effective approach is to establish different quarantine rules for immune and nonimmune individuals, where rules should depend on viral transmissibility after vaccination or infection. Altogether, our study provides quantitative information for contact tracing downsizing in vaccinated populations or in populations that have already experienced large community outbreaks, to guide COVID-19 exit strategies.

Is SARS-CoV-2 elimination or mitigation best? Regional and disease characteristics determine the recommended strategy

“…Therefore, new mathematical tools are urgently needed to quantitatively optimize the trade-off between elimination and mitigation. We also emphasize that for proper quantitative comparison of response strategies, future modelling should explicitly consider a distinction between community cases and travel-related cases, and include statistics that are relevant for the characterisation of community outbreaks occurring when an elimination strategy is implemented, such as the efficiency of border testing and quarantine policies and the probability of a traveller initiating a community outbreak [128, 47, 101, 107, 106], the expected size of such an outbreak [88, 38, 44], the probability that a community outbreak has been eliminated, such that strict NPIs might be relaxed [86, 14, 79], vaccination strategies [69, 89] and elimination exit strategies [47, 70, 115] for regions with low infection prevalence.…”

“…The World Health Organization defines an outbreak as over when two incubation periods have passed with no further cases reported (i.e., 28 days for COVID-19 [86]), however, a more precise approach could be to relax measures when there is a high probability that the number of cases in the community is zero [86]), and to consider how quickly the reported cases were isolated. Contact tracing efficiency and population compliance will affect when community NPI relaxation can feasibly occur [70, 17]. Thus, faster reopening may occur in regions characterised by social cohesiveness, such as rural areas where ‘everyone knows everyone’, and where infected people and their contacts are easier to identify and reach [121, 64].…”

Edukasi Kesehatan: Covid-19 Dan Penelusuran Kontak

“…Penelusuran kontak yang dikombinasikan dengan karantina, adalah komponen kunci keberhasilan pengelolaan pandemi COVID-19 (Martignoni et al, 2022) ; (Vogt et al, 2022). Kontak yang teridentifikasi dilacak dan dikarantina, dan pelacakan cepat secara signifikan memperlambat, atau bahkan mencegah, penyebaran epidemi, dengan mengkarantina individu yang terinfeksi (Martignoni et al, 2022). Karantina, pelacakan kontak, screening, dan isolasi adalah tindakan pencegahan COVID-19 yang efektif, terutama jika diintegrasikan bersama (Girum et al, 2020).…”

Is SARS-CoV-2 elimination or mitigation best? Regional and disease characteristics determine the recommended strategy

“…Shaded cases correspond to hospitalized cases. The width of a person corresponds to the average duration of an active case and the relationship between incidence, prevalence and hospital occupancy is investigated in the electronic supplementary material, section A (figure adapted from [ 14 ]). …”

“…When high transmissibility does not allow for periods with no community cases between outbreaks, and when the risk of severe disease is relatively low, elimination is no longer feasible, and mitigation is preferred. Estimates used for producing the figure and their derivation are provided in the supplementary information, section B (adapted from [ 14 ]). …”