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New Delhi, Jul 21: The Centre has written to all states and union territories warning against the use of N-95 masks with valved respirators by people, saying these do not prevent the virus from spreading out and are "detrimental" to the measures adopted for its containment.

The Director General of Health Services (DGHS) in the Ministry of Health, in a letter to the Principal Secretaries of health and medical education of states, said it has been observed that there is "inappropriate use" of N-95 masks, particularly those with valved respirators, by the public other than designated health workers.

The DGHS referred to the advisory on the use of homemade protective cover for face and mouth available on the website of the Ministry of Health.

"It is to bring to your knowledge that the use of valved respirator N-95 masks is detrimental to the measures adopted for preventing the spread of coronavirus as it does not prevent the virus from escaping out of the mask. In view of the above, I request you to instruct all concerned to follow the use of face/mouth cover and prevent inappropriate use of N-95 masks," DGHS Rajiv Garg said in the letter.

The government had in April issued an advisory on the use of homemade protective cover for face and mouth, asking people to wear it, particularly when they step out of their residences.

The advisory stressed such face covers must be washed and cleaned each day, as instructed, and stated that any used cotton cloth can be used to make this face cover.

The colour of the fabric does not matter but one must ensure that the fabric is washed well in boiling water for five minutes and dried well before making the face cover. Adding salt to this water is recommended, it said.

It also listed the procedures of making such homemade masks, asking to ensure it fits the face well and there are no gaps on the sides.

It urges people to wash hands thoroughly before wearing the face cover, switching to another fresh one as the face cover becomes damp or humid, and never reusing it after single use without cleaning it.

"Never share the face cover with anyone. Every member in a family should have separate face cover," the advisory stated.

India's COVID-19 case tally crossed the 11-lakh mark on Monday, while the total number of recovered patients increased to over seven lakh, according to Union health ministry data.

The death toll due to the disease rose to 27,497 with 681 fatalities reported in one day.

The ministry data updated at 8 am on Monday showed that a record single-day jump of 40,425 COVID-19 cases had taken the total number of cases to 11,18,043.

Jun 13: Requiring the wearing of masks to prevent the spread of the novel coronavirus in areas at the epicenter of the global pandemic may have prevented tens of thousands of infections, a new study suggests.

Mask-wearing is even more important for preventing the virus' spread and the sometimes deadly COVID-19 illness it causes than social distancing and stay-at-home orders, researchers said, in the study published in PNAS: The Proceedings of the National Academy of Sciences of the USA.

Infection trends shifted dramatically when mask-wearing rules were implemented on April 6 in northern Italy and April 17 in New York City - at the time among the hardest hit areas of the world by the health crisis - the study found.

"This protective measure alone significantly reduced the number of infections, that is, by over 78,000 in Italy from April 6 to May 9 and over 66,000 in New York City from April 17 to May 9," researchers calculated.

When mask-wearing went into effect in New York, the daily new infection rate fell by about 3% per day, researchers said. In the rest of the country, daily new infections continued to increase.

Direct contact precautions - social distancing, quarantine and isolation, and hand sanitizing - were all in place before mask-wearing rules went into effect in Italy and New York City. But they only help minimize virus transmission by direct contact, while face covering helps prevent airborne transmission, the researchers say.

"The unique function of face covering to block atomization and inhalation of virus-bearing aerosols accounts for the significantly reduced infections," they said. That would indicate "that airborne transmission of COVID-19 represents the dominant route for infection."

The U.S. Center for Disease Control and Prevention on Friday urged organizers of large gatherings that involve "shouting, chanting or singing to strongly encourage the use of cloth face coverings to lower the risk of spreading the coronavirus."