As migrants pour in to their villages from urban Covid hotspots, they pose a growing challenge to states fighting to keep the viral load down: how to quarantine them, in large numbers, for at least 14 days and how to maintain social distancing during that quarantine given that most of them are asymptomatic.

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Defining the challenge, AIIMS Director Randeep Guleria, member of the high-level Covid committee, said: “We must remember that these migrants can be asymptomatic but are carrying the infection. That is why isolation is most important. Only that will prevent the spread, rather than just testing symptomatic patients. Also, the number of migrants is huge. Testing.will run into lakhs.”

The numbers are a challenge. An analysis of the train network opened for the migrants shows that of the 1000 Shramik Special trains that have run since May 1 to May 15, until over two-thirds of them, or 668, originated from Red zones and as many as 508 of them moved passengers to Green or Orange zones.

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In other words, an estimated 8 lakh migrants, assuming each train carried the designated 1,200 passengers, moved from Red zone “hotspots” (classified based on case load, doubling rate, extent of testing) to districts.

Most Shramik trains from Red zones, isolating migrants new challenge that have either been Covid-free for the past 28 days (Green) or are in Orange zones, which are classified as neither Green nor Red.

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Just 71 trains originated from locations designated as Green zones. Of these, 30 terminated in Green zones, 17 in Red zones and the rest in Orange zones.

Of the destination stations, most fall in states like Bihar, Uttar Pradesh, Jharkhand, Odisha, Madhya Pradesh and West Bengal. As many as 295 are in Green Zones, 223 are in hotspots while 482 are in Orange zones.

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“As people travel home from hotspots, chances of migrants turning positive are higher,” said Guleria, who heads the mentoring team for Bihar, one of the primary destination states for migrants. “The strategy has to be to prevent that spread of infection in rural communities. So it is important that they are quarantined for 14 days and those who are symptomatic are tested; those tested, are isolated and treated in Covid care centres, so that the chain of transmission is broken. And only those who remain asymptomatic should be allowed to go into the community,” Guleria said.

His remarks assume significance given that more than 350 trains moved from origin districts that have more than a 500-case difference from the train’s destination district. Uttar Pradesh had 206 trains coming in from districts that have more than 500 cases than the destination district. Bihar is receiving the most trains, 55 of 184, that are travelling from red to Green.

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Many of the migrants are on the younger side and may have a milder form of infection or remain asymptomatic, said K Srinath Reddy, president of Public Health Foundation of India and member of the Covid high-level committee.

“But the important thing is to prevent transmission from them to others. It means they have to be isolated not only non-infected outsiders but also kept in relative isolation from each other, so that the viral load become less for each person. Otherwise, if they keep exchanging the virus, viral load will not come down,” Reddy said.

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The Indian Express reported how a high positivity rate is being seen among migrant workers returning to Bihar. Said the state’s Principal Health Secretary: “Our challenge is to save our home population from getting infected from migrants coming to Bihar since the last week of April”.

The Health Ministry also announced last week a surveillance survey to test returning migrants.

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Classification of zones has been mired in controversy with states like West Bengal objecting to the definitions set by the Centre.

Among the source stations, mostly in Gujarat, Maharashtra, Karnataka, Telangana, Kerala, Andhra Pradesh, Tamil Nadu and Punjab, 668 are in hotspots, 71 are in Green and 261 are in Orange zones.

The most number of trains have originated from Gujarat. Data shows that Surat, which saw multiple incidents of unrest and violence involving stranded migrant workers, sent out around 128 trains so far and plans to send another 20 immediately taking the total tally to around 148 – the most for any one source station in India, mostly to Uttar Pradesh, and other states. Gujarat, incidentally, has sent the most number of the 1000 trains so far.