Dr Sujeet K Singh, the director of the Union health ministry’s National Centre for Disease Control (NCDC), who has been spearheading India’s Covid-19 surveillance strategy through the centre’s integrated disease surveillance programme network, spoke to Rhythma Kaul about the implications of Delhi’s sero surveillance findings; the strategy to deal with the disease outbreak in the wake of these results; and whether it means people have developed immunity against the disease, among other issues. Edited excerpts:
Delhi’s sero surveillance results are out. What does the data imply?
The implications can be interpreted both ways — the positive side to it is that the city has definitely crossed its peak as far as Covid is concerned, and that the fear of case explosion in the city that we were grappling with a month or so ago is gone. The exponential increase of cases in Delhi is not a worry anymore. The challenge, however, is that it cannot be said categorically that the outbreak has ended as there is still susceptible population — about 77% as per the sero surveillance data — and cases are still being reported. So we cannot afford to drop our guard or be complacent. We have to be vigilant at all times and follow all preventive measures to the T.
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Now that the Delhi sero surveillance data is out, what impact will it have on the containment measures?
It is important data to guide containment strategies from now on. Earlier, same measures were being used, but now we have the opportunity to devise a customised approach both for low prevalence and high prevalence districts. For example, in some eight districts where the disease prevalence was found to be quite high (above 20%), the focus now will be on identifying the population at risk and bringing it under surveillance. The high-risk population would be the people above 60 years of age, and those who are immuno-compromised because of any health conditions. These people need special focus, as this section has stayed protected by being largely indoors all these months. Those districts with low prevalence will need us to start aggressively testing, tracking and treating its population, as these districts have higher percentage of susceptible population that has not been exposed to the virus.
Will there be any follow up of this surveillance exercise?
This exercise cannot be a one-off and needs to be repeated periodically to know the exact burden from time to time. The figures that we have today are not current figures as most samples were collected between June 27 and July 5, and the infection must have happened around mid-June because it takes about two weeks for IgG antibodies to develop. To establish a trend this type of survey needs to be repeated and it will be repeated in coming months.
Will there be any follow-up studies done related to this sero-survey to know more about the quality of antibodies or duration of its presence in the body?
We will be following up on the results as there is lots more that we need to know. We will be monitoring a select population from the number of 20,000-odd people surveyed for this sero surveillance on a regular basis, especially those who have shown a high volume of antibodies (titre) in their sample. These people will be monitored at three months, six months and till the completion of a year, to see whether they still posses antibodies against the disease, and even if they do how has the volume changed over a period of time.
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What is the significance of knowing that these many people have developed antibodies; does it mean they have protection against the disease?
Since these many people have developed antibodies there will be some immunity against the disease; however, what is pertinent to determine is the level of immunity; whether there will be reinfection among recovered patients, or will there be longer immunity against it. We don’t have answers to these crucial questions yet; and evidence for or against it needs to be established through robust scientific studies.
What is one thing that you are most happy about from the survey results?
The biggest silver lining for me is that if we have such high population that was exposed in past but did not largely display serious symptoms or succumbed — then it as good as a vaccine.