Abstract
India’s lockdown and subsequent restrictions against SARS-CoV-2, if lifted without any other mitigations in place, could risk a second wave of infection. A test-and-isolate strategy, using PCR diagnostic tests, could help to minimise the impact of this second wave. Meanwhile, population-level serological surveillance can provide valuable insights into the level of immunity in the population. Using a mathematical model, consistent with an Indian megacity, we examined how seroprevalence data could guide a test-and-isolate strategy, for fully lifting restrictions. For example, if seroprevalence is 20% of the population, we show that a testing strategy needs to identify symptomatic cases within 5–8 days of symptom onset, in order to prevent a resurgent wave from overwhelming hospital capacity in the city. This estimate is robust to uncertainty in the effectiveness of the lockdown, as well as in immune protection against reinfection. To set these results in their economic context, we estimate that the weekly cost of such a PCR-based testing programme would be less than 2.1% of the weekly economic loss due to the lockdown. Our results illustrate how PCR-based testing and serological surveillance can be combined to design evidence-based policies, for lifting lockdowns in Indian cities and elsewhere.
Highlights
The emergence of the novel virus SARS-CoV-2 has prompted stringent physical distancing measures around the world
In the event that the lockdown is effective in controlling transmission, its release results in a resurgent epidemic, that can be sufficiently severe to overwhelm the health system, i.e. with the number of persons needing hospitalization exceeding the existing hospital capacity
A less effective lockdown does not see any resurgent epidemic upon being lifted. We note that these overall dynamics are consistent with previous modelling findings in other s ettings[6]
Summary
The emergence of the novel virus SARS-CoV-2 has prompted stringent physical distancing measures around the world. Some proposed strategies include (i) a cycle of lockdowns and r eleases[6,8], to maintain any resurgent epidemic to within levels manageable by the health system, and (ii) the use of serological tests to identify those who have had exposure to the virus, and might be presumed safe to return to normal a ctivity[9] For the latter to be implemented, there needs to be high confidence in the serological test being used, that it has minimal risk of false positivity. The former strategy may face real challenges in such a complex society as in India, in view of the effect of such measures amongst the most d isadvantaged[10] Another strategy involves the use of systematic and intensive testing, to identify and quarantine cases of SARS-CoV-2 infection as early as possible. How should decisions about post-lockdown testing strategy be made in the face of such uncertainty?
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