Study decodes Covid risk with proximity, duration of exposure to infected person

British researchers have discovered how the risk of Covid infection varies with proximity and duration of exposure to an infected personTo understand the likelihood of SARSCoV2 transmission after exposure researchers from the University of Oxford UK used data from the NHS Covid app with 7 million contacts in England and WalesTheir study published in the journal Nature revealed that more than proximity the duration of exposure to people with Covid may increase the likelihood of infectionLonger exposures at greater distances had a similar risk to shorter exposures at closer distancesThe probability of transmission confirmed by a reported positive test increased initially linearly with the duration of exposure 11 per cent per hour and continued increasing over several daysWhile most exposures were short transmissions typically resulted from exposures lasting one hour to several daysHouseholds accounted for about 6 per cent of contacts but 40 per cent of transmissionsWith sufficient preparation privacypreserving yet precise analyses of risk that would inform public health measures based on digital contact tracing could be performed within weeks of a new pathogen emerging said Luca Ferretti from Oxfords Department for MedicineThe study analysed 7 million Covid contacts from the app between April 2021 and February 2022 involving 23 million hours of exposure and 240000 reported positive testsContacts were assessed based on proximity duration and infectiousness scores as calculated by the app which were then used to estimate the transmission riskThe results showed immediate implications for contact tracingWe found that the cumulative duration of exposure to infected individuals is a key predictor of transmission in the Covid19 pandemic and needs to be accounted for in preparation for future epidemics of respiratory pathogens Ferretti saidSince duration of exposure to known cases can usually be recalled without the support of digital tools it could be immediately incorporated into manual contact tracing interviews the researchers saidThe researchers said if deployed at scale contact tracing apps for infectious diseases have potential not only as interventions to reduce transmission but also as tools to develop quantitative epidemiological understandingDoing this and translating it into improved interventions takes timeWe should strive to accelerate and improve this process as a key step toward preparedness for future epidemics the researchers said in the paperThey called for the development of tools and methods for quantitative risk measurement and to integrate them into the public health toolbox for the benefits they can bring now and in readiness for rapid deployment at the start of the next pandemic