Stop the virus before it can strike, says S.Ananthanarayanan.

Renyi Zhang, Yixin Lib, Annie L. Zhang, Yuan Wang, and Mario J. Molina, from the Texas A&M University, University of Texas at Austin, CALTECH, Pasadena and University of California, San Diego describe in the journal, Proceedings of the Academy of Science, their finding that “airborne transmission via respiratory aerosols represents the dominant route for the spread of COVID-19.”

The journal, Science, had recently carried a report about the size of droplets that a person infected with Covid-19 sends out when she speaks or coughs. The report said the smaller droplets evaporated and released the virus as an aerosol, or a mist that stayed airborne for hours. The group writing in PNAS has analysed the measures taken, from time to time, in China, Italy, New York and the USA, and it finds that the use of masks is the crucial step and does the most to block the spread of the virus.

Our analysis of the trend and mitigation measures in Wuhan, China, Italy, and New York City, from 23rd January to 9th May 2020, reveals that the difference with and without mandated face covering represents the determinant in shaping the pandemic trends in the three epicenters. This protective measure alone significantly reduced the number of infections, that is, by over 78,000 in Italy from 6th April to 9th May and over 66,000 in New York City from 17th April to 9th May,” says the paper In PNAS.

The study is centred around the trend of confirmed infections and confirmed deaths from Covid-19 from 23rd Jan to 9th March 2020. The report recalls that the COVID-19 outbreak emerged during December 2019 in Wuhan, China and the numbers in China dominated the global trend during January and February 2020, as can be seen from the first graph. From February, however, the rise of newly confirmed cases and fatalities in China has almost flattened. In contrast, the numbers in other countries show a sharp increase from the beginning of March. The epicenter shifted from Wuhan to Italy in early March and to New York City (NYC) in early April. By April 30, the numbers of confirmed COVID-19 cases and deaths, respectively, reached over 200,000 and 27,000 in Italy and over 1,000,000 and 52,000 in the United States, compared to about 84,000 and 4,600 in China. We can see from the graph that the curves in Italy exhibit a slowing trend from mid-April, while the numbers in the world and the United States continue to increase.

The curve flattening in China can be attributed to extensive testing, quarantine, and contact tracing, and then aggressive measures of lockdown of all cities and rural areas in the whole country, isolation of residents having close contact with infected people, and mandated wearing of facemasks in public. How effective the mitigation measures were has not been rigorously evaluated, and making out which measure was more effective is challenging, the report says, since all measures were implemented at the same time in January 2020.

In Italy also, the measures of quarantine, isolation and city lockdown were implemented, right from 9th March. But we can see that the numbers kept rising, at least until mid-April. In most of the USA too, social distancing, quarantine and isolation was started in March and April, on 22nd March in New York City. But the continuous rise in infections makes it evident that the measures were not effective. The difference in Italy and the USA, in contrast with China, is that using facemasks was not ordered and was not common during the early stages of the pandemic. WHO issued the guideline only on 6 April. Facemasks were ordered in northern Italy on the same day and nation-wide on 4th May. It was ordered in New York on 17th April.

Unlike in China, where social distancing and masking were introduced simultaneously, the measures were introduced many weeks apart in Italy and New York. The change in the infection trend can thus be made out, to see the effect of masking. The third graph brings out the timing of the different measures, and their effects.

direct contract transmission – but do not seem to prevent infection through inhalation of virus-bearing aerosols, which can disperse, or through smaller droplets at shorter distances. While we can see the downward turn with the introduction of masks, the dotted lines show where the linear trend would have led – and statistical methods have estimated the number of infections prevented by masking.

“With social distancing, quarantine, and isolation in place worldwide and in the United States since the beginning of April, airborne transmission represents the only viable route for spreading the disease, when mandated face covering is not implemented. Similarly, airborne transmission also contributes dominantly to the linear increase in the infection prior to the onset of mandated face covering in Italy and NYC. Hence, the unique function of face covering to block atomization and inhalation of virus-bearing aerosols accounts for the significantly reduced infections in China, Italy, and NYC, indicating that airborne transmission of COVID-19 represents the dominant route for infection,” the report says.

Implications for India

The situation in India is different in the sense that there are concentrations, like slums, which we do not see in the west. For all that, there is alarming rise in numbers even 85 days after total lockdown. The report in PNAS cites a recent finding that “the highest viral load in the upper respiratory tract occurs at the symptom onset, suggesting the peak of infectiousness is on or before the symptom onset.” While India has a problem of crowding and numbers to handle, that major role of airborne transmission by asymptomatic carriers in spreading the infection is an indicator of the direction that we should take. There was marked decline the progress of the disease in Italy and New York, with the introduction of masking. Ensuring the discipline of masking, especially in places with concentration of people, seems to be the path that India should follow, to get that rising curve to flatten out.