In the most extreme effort yet to slow the march of coronavirus in the U.S., the Centers for Disease Control and Prevention recommended that events of 50 people or more not be held for about two months.

For the next eight weeks, organizers should cancel or postpone in-person events of that size throughout the U.S., the agency said on its website Sunday. When feasible, organizers could modify events to be virtual.

The advisory doesn’t apply to the day-to-day operation of organizations such as schools, institutes of higher learning, or businesses – although many of those entities have taken steps of their own.

U.S. authorities are focusing on “flattening the curve” of the virus’s spread, to prevent health care and other facilities from becoming overwhelmed.

“This recommendation is made in an attempt to reduce introduction of the virus into new communities and to slow the spread of infection in communities already affected by the virus,” the CDC said.

Examples of the events that shouldn’t be held for now include conferences, festivals, parades, concerts, sporting events, weddings, and other types of assemblies.

“Events of any size should only be continued if they can be carried out with adherence to guidelines for protecting vulnerable populations, hand hygiene, and social distancing,” the CDC said.