China's top respiratory expert Zhong Nanshan recently talked about a new pattern of COVID-19 transmission in China: environment to human.

What is environment-to-human transmission? Is it a new COVID-19 transmission route? How can it be prevented? Let's find out in this episode of Answer Bank.

Environment-to-human transmission refers to the transfer of virus from virus-laden objects to humans upon contact.

In general, viruses can survive longer on surface of objects because they have a lower temperature than the human body.

So far, most cases of environment-to-human transmission in China have been found to be linked with imported products, such as frozen foods.

According to a study published in a leading medical journal The Lancet, titled "Stability of SARS-CoV-2 in different environmental conditions," the novel coronavirus has a lifespan of about three hours on paper and tissue paper, two days on wood, four days on glass and banknotes, and seven days on the surface of a surgical mask. However, the threshold for virus concentration before infection still remains unclear.

According to Chinese Center for Disease Control and Prevention's Chief Epidemiologist Wu Zunyou, environment-to-human transmission can only happen under the following three conditions:

1. The object is seriously contaminated by the virus.

2. The object's surface is able to keep the virus alive for a fairly long time.

3. The person coming in contact with virus-laden objects does not take adequate protection measures.

If one comes into contact with virus-laden objects but keeps a mask on and washes hands immediately after, the transmission can be avoided.

It must be remembered that environment-to-human transmission is not a new route of transmission. The main transmission route of COVID-19 is still human-to-human.

Wu said virus transmission from objects to human often occurs in the early stage of a pandemic. While it may be a trigger, its role in the spread of the disease is very limited.

In a nutshell, environment-to-human transmission can be avoided by taking protective measures, such as wearing a mask and washing hands.

Cameraman: Danzeng Jiancuo

Video editor: Ge Kai

Cover image: Li Yueyun