The U.S. Centers for Disease Control on Monday shortened the recommended isolation and quarantine guidelines for Americans who contract or are exposed to Covid-19 from 10 to five days. The move drew swift criticism from many experts, who questioned the logic behind the decision.

“I don’t think there’s any big change in science that justifies a change in guidance,” said Lawrence Gostin, director of the World Health Organization’s Collaborating Center on National and Global Health Law. In his view, the guidance “has much more to do with societal function than to do with science.”

One of the biggest criticisms was that shortening the isolation and quarantine requirement should be augmented with a negative test requirement. Today, California did exactly that with its updated guidelines.

The guidance issued by the state’s public health director, Tomás Aragón, mostly aligns with the new CDC recommendations, but it contains “additional testing recommendations to exit isolation and quarantine and improved masking measures.”

The California framework says “local health jurisdictions may be more restrictive” and allows that residents who have received booster shots “do not have to stay home but should test on day five.”

The new Golden State guidelines add that all Covid-positive individuals can end isolation after day five if symptoms are not present (or are resolving) and if an antigen test collected on day five or later is negative. It also says unvaccinated individuals — or vaccinated but unboosted people — who are exposed to Covid “should stay home for at least five days and also get an antigen test on day five.”

The framework encourages upgrading mask quality, given the transmissibility and prevalence of Omicron. It says, “all persons should optimize mask fit and filtration, ideally through use of a surgical mask or respirator.”

Los Angeles County’s Director of Public Health indicated today that the county would be aligning with the state’s guidelines.