The sero surveillance map explains why COVID-19 cases are dipping but we can’t let up on vigilance and testing
Just like everything else, disease-mapping is a crucial component in the fight against COVID-19 as it helps to formulate mitigation strategies and recalibrate them according to evolving situations. And as the virus chases us, it helps us strategise on ways to outrun it and chase it instead. It is in this respect that Delhi’s first sero surveillance, or tracking the antibodies of its residents, has given us a fair idea about the extent to which the disease has spread in the city. So much so that Delhi Health Minister Satyendar Jain, himself recovered from COVID-19, has announced that such surveillance will be held every month to assess preparedness to combat the disease and reset response mechanisms given the mutating strains of the virus. Many would say that with one in about four Delhiites affected and with about 23.5 per cent of the total samples tested found to have antibodies or past history of infection, the spread is big enough and rapid. But given Delhi’s population is two crore, this means that nearly 47 lakh people may have contracted the infection already and probably even recovered without knowing, considering that antibodies appear in the blood after three weeks of the infection. So though far away from herd, there is at least some immunity. The high positivity rate varied zonally, highest in the New Delhi area, and lowest in the southwest. The mortality rate continues to be the same as in April end, at 0.07 per cent, so there is a possibility that the virus is yet to let up as over 70 per cent of the population has still not been affected. On the positive side, the high sero-prevalence among a densely-packed population means the city may have crested or is cresting the peak, that we may have scraped through within limits and the case explosion may not be as high as expected. While experts want this pattern to hold, the flattening responsibility is on us. And that can be possible only when we are not complacent about strict vigilance, preventive behaviour and what is now being called compliance with a COVID-appropriate code. So far, the enforcement of rules has largely been top-down, officially sanctioned and all-enveloping. But that cannot be unending and as we unlock layers of permissive behaviour, a lot of discipline has to come from people and communities themselves. Of course, this mapping will undoubtedly help in devising containment strategies for low and high density areas and ease off the blanket approach in some places, which have been sealed in for over 90 days. Sealing plans can now be customised according to the intensity of disease prevalence and transmission possibility. There could be more surveillance in such identified spots. But it is the low prevalence or virgin zones that the virus is waiting to consume at the slightest drop of guard. Besides, most of the high risk group, the elderly, children, those with co-morbidities and immuno-suppressed, have largely been indoors and some degree of restlessness is now affecting them, too. So testing must be ramped up in seemingly green zones and a watch kept on isolated cases springing up in unexpected places. In fact, these new cases should be hunted down with aggressive contact testing, isolation and treatment. Given the contiguous existence of Delhi and the National Capital Region (NCR), a sero surveillance must be done across all zones periodically to arrest the spiral, force the curve down and hold it there. In fact, the COVID response module for Delhi-NCR needs to be seamless and coordinated if we do not want resurgence of any kind.
Of course, there are many questions about the lastability of antibodies and immunity. Worldwide research is on to analyse re-infection among recovered patients, with some studies showing rapid antibody depletion in about two months and some predicting that re-occurrence is rare before six months. And while these predictions need to be backed up by scientific evidence and the promised vaccine has some time coming, given its untested protective worth against the Indian strain, we still have to fall back on basics — social distancing, hand hygiene and mask-wearing. And not slacken up on preparedness. If anything that the estimates of the city’s caseload crossing five lakh by the end of July have done, it is to perk up the healthcare infrastructure and step up testing and early treatment, which have led to a drop in cases. Delhi now has more than 15,000 beds in hospitals for COVID care and has increased its critical care infrastructure. As more than 80 per cent of COVID patients do not require hospitalisation, the home quarantine allowance has helped people come out for testing than hide symptoms for fear of being carried away to an institutional facility. Testing still has to be more aggressive though given our population and more private labs need to be certified for conducting them. Yes, the rapid antigen tests are quick but not accurate and show up negative even when a swab test confirms positivity. So swab tests are the way to go forward and though it may not be possible to cover every antigen-tested patient, at least testing should cover a wider arc of the population. For Delhi has mostly asymptomatic cases, a silent threat that is waiting to explode. The city needs to keep a plan ready for a year at least.