CNN  — 

The new coronavirus spreads mainly via airborne transmission and wearing a mask is the most effective way to stop person-to person spread, according to a new study.

A team of researchers in Texas and California compared Covid-19 infection rate trends in Italy and New York both before and after face masks were made mandatory. Both locations started to see infection rates flatten only after mandatory face mask measures were put in place, according to the study published Thursday in the Proceedings of the National Academy of Sciences

The researchers calculated that wearing face masks prevented more than 78,000 infections in Italy between April 6 and May 9, and more than 66,000 infections in New York City between April 17 and May 9.

“Wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with simultaneous social distancing, quarantine, and contact tracing, represents the most likely fighting opportunity to stop the COVID-19 pandemic, prior to the development of a vaccine” they wrote.

The researchers gauged the effectiveness of different strategies for stopping the spread of infection and to determine how the virus is mainly spread. Viruses can spread by direct contact when a person coughs or sneezes on another person; indirect contact, when a person coughs or sneezes on an object that is then touched by another person; or in the air via large droplets that fall quickly to the ground and tiny droplets, called aerosols, that can travel several feet and hang in the air for a while.

To determine how the main transmission method of the virus, the researchers analyzed trends in the infection rates in three epicenters of the pandemic – Wuhan, China, Italy, and New York City. They looked at mitigation measures that were being used at those locations, like extensive testing, quarantining, contact tracing, social distancing and mandatory use of face masks.

The researchers then compared the timing of when those measures were put in place. In China, all of the measures were put