At a time when the lengths that humanity is going to throw the novel coronavirus out of our lives seems to be matched only by the strides that the virus itself is making with trickier variants and deadlier surges, new guidelines issued by authorities point to the need for guarding more strictly against how the virus seems to be spreading. This month, advisories by the US CDC and experts in India have given an updated picture of transmission of the virus and suggested strategies for dodging the infection.
So, What Is New?
Not so much new, but a reiteration of aerosol spread of the virus was made by the Principal Scientific Adviser to the Prime Minister, K VijayRaghavan, who urged people to consciously adhere to ventilation strategies shared by his office to prevent the virus from causing infections at their homes and other spaces within which they may move.
“Saliva and nasal discharge in the form of droplets and aerosols carry the virus from one person to another," the advisory said, adding that, “(i)n closed un-ventilated indoor spaces, droplets and aerosols become quickly concentrated and greatly increase the risk of transmission to people in the area".
The advisory by Prof. VijayRaghavan follows an update that the the US Centres for Disease Control and Prevention (CDC) made to its Covid-19 transmission guidelines on May 7 in which it suggested that aerosol transmission was the top mode of spread of the infection. Interestingly, however, the US public health watchdog has effected a series of flip-flops on the question of transmission of the novel coronavirus and the latest amendment reflects what members of the global scientific community had been suggesting for long.
In the updated advisory, CDC says that among the three key means by which people are exposed to virus-bearing respiratory fluids is the “(i)nhalation of air carrying very small fine droplets and aerosol particles that contain infectious virus". The remaining modes were “(d)eposition of virus carried in exhaled droplets and particles onto exposed mucous membranes [for example, the eyes, nose etc]." and touching of eyes or mouth with hands that have been contaminated with respiratory fluids carrying the virus.
But it is CDC’s acknowledgement of aerosol spread that stood out, especially after it first added back in September last year, and then removed within days, advice that it was “possible” that the novel coronavirus spreads via airborne transmission.
The CDC maintained though that droplets spread is not to be underestimated, saying that “(r)isk of transmission is… greatest close to an infectious source where the concentration of these exhaled droplets and particles is greatest". But it did underline the risk inherent in aerosol spread, noting that “(t)he largest droplets settle out of the air rapidly, within seconds to minutes. The smallest very fine droplets, and aerosol particles formed when these fine droplets rapidly dry, are small enough that they can remain suspended in the air for minutes to hours".
Distance Keeps Loved Ones Closer
The updated CDC guidelines, too, notes the factor of distance in aerosol transmission and, while stating that “although infections through inhalation at distances greater than six feet from an infectious source are less likely than at closer distances, the phenomenon has been repeatedly documented under certain preventable circumstances". It adds that such transmission in closed spaces can involve concentrations of virus particles exhaled over an extended period of more than 15 minutes and up to hours and is “sufficient to transmit infections to people more than 6 feet away…"
This brings us straight to the question of distancing to check the spread of the novel coronavirus. While the CDC wordings seem to stick to the 6-feet distance rule, the Indian advisory says “(a)erosols can be carried in the air up to 10 metres". In that respect, the guidance by the Principal Scientific Adviser’s office presents a different view from the one mentioned in other government advisories, including the Clinical Management Protocol for Adults released on May 24, which states that the virus spreads mainly between people “within 1 metre" of each other although it warns against aerosol spread and poor ventilation, as does the World Health Organisation (WHO)’s most recent advisory, updated in April.
Need Of The Hour: To Clear The Air
What the guidelines by the Principal Scientific Adviser stress on is the need for proper ventilation across spaces that can be a site for people to collect, be it the home, office or public transportation. The advisory notes that “(j)ust as smells can be diluted by ventilation, the dangerous concentration of the virus can be reduced by ensuring that outdoor air flows in".
For homes, it says care must be taken to “let outdoor air flow in to displace indoor air. This directional air flow and improved ventilation can lower the potential for infection from accumulated viral load in closed spaces".
For hutments, it warns that lack of a window or cross ventilation can enable excessive viral load to gather and urges gram panchayats to ensure that “jaali/air outlets with exhaust fans are installed… in homes where there is no cross-ventilation".
For offices with indoor cooling, it talks of keeping windows and doors ajar and adding an exhaust fan for improving air circulation. Spaces that have central cooling should go for “improved central air filtration or increased filtration efficiency" it says, adding that roof ventilators and HEPA/regular filters are recommended in offices, auditoriums, shopping malls, etc.
Buses and trains should also keep windows open where possible and exhaust systems could be introduced to improve airflow in air-conditioned vehicles, which feature HEPA/regular filters.
Apart from ventilation, the advisory urges the need for double-masking, saying that masks should be worn while stepping outside of home and also at home when outsiders are visiting. For double masking, it recommends that one should wear a surgical mask and then a tight-fitting cloth mask over it. Those who do not have a surgical mask, can wear two cotton masks together, the advisory says, adding that even a double layer cotton homemade mask is better than none while an N95 mask offers maximum protection.
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