By Stephanie Nebehay and Andrea Shalal

GENEVA/WASHINGTON (Reuters) – The World Health Organization on Friday said that medical masks should be prioritised for health workers, but it opened the door to greater public use of homemade masks or other mouth coverings as a way to reduce the spread of the coronavirus.

A senior WHO official told reporters there was some possibility of airborne transmission of the virus that has now infected over 1 million people and killed 50,000 people worldwide since emerging in China last December.

But the main driver of the pandemic was still believed to be sick people with symptoms who were coughing and sneezing and contaminating surfaces or other people.

“We must preserve medical surgical respirator masks for our frontline workers. But the idea of using respiratory coverings or mouth coverings to prevent coughing or sneezing projecting disease into the environment and towards others … that in itself is not a bad idea,” Dr. Mike Ryan, the WHO’s top emergencies expert, told a news conference.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Disease who is top U.S. infectious disease official, said on Friday that Americans should cover their face if they have to go in public, but they should still stay isolated as much as possible.

Ryan acknowledged a “very important and healthy debate” on the wearing of masks.

He said that if used, they should be part of a comprehensive strategy and would not negate the need for handwashing and social distancing.

“So we can certainly see circumstances in which the use of masks, both homemade or cloth masks, at community level may help in an overall comprehensive response to this disease,” he said.

Ryan, citing data from Italy, said that there did not appear to be a link between people taking drugs against hypertension known as ace inhibitors and getting the disease or developing severe disease.

Click in a separate browser for a GRAPHIC on global tracking of the spread of the coronavirus.

Exhausted staff in some overwhelmed health care systems could be a factor in mortality rates, Ryan said, adding: “We need to reduce the tsunamis of patients coming through the door to give doctors, nurses and other carers the opportunity to save more lives.”

Dr. Maria van Kerkhove, a WHO epidemiologist, cautioned against comparing mortality rates between countries, noting that some may be missing mild infections as they focus on patients in severe condition.

“What we really need to be focusing on right now is what is the age profile of people who are in ICU (intensive care units),” she said.

“We are seeing more and more individuals who are of the younger age group – in their 30s, in their 40s, in their 50s – who are in ICU and who are dying,” she said, citing Italy and China.

Generally older people or those with underlying medical conditions will have more advanced disease and a higher risk of death, van Kerkhove said.

“But we have some time to go before we can really understand what mortality looks like across different countries so I would urge you to take those mortality rates with caution when comparing across countries,” she said.

(Reporting by Stephanie Nebehay in Geneva and Andrea Shalal in Washington, Editing by Rosalba O’Brien and Grant McCool)