Here are some of the latest health and medical news developments, compiled by the editors of HealthDay:
WHO Backpedals on Claim That Spread of Coronavirus by People Without Symptoms is Rare
A claim that transmission of the COVID-19-causing coronavirus by people without symptoms is "very rare" was quickly reversed by the World Health Organization.
That assertion was made Monday at a media briefing by WHO official Dr. Maria Van Kerkhove. On Tuesday, she said the statement was based on just two or three studies and that it was a "misunderstanding" to say that transmission by people without symptoms is rare, The New York Times reported.
"I was just responding to a question, I wasn't stating a policy of WHO or anything like that," Van Kerkhove said.
The WHO was criticized for causing confusion about such an important public health issue.
"All of the best evidence suggests that people without symptoms can and do readily spread SARS-CoV-2, the virus that causes Covid-19," according to a statement released Tuesday by scientists at the Harvard Global Health Institute, The Times reported.
"Communicating preliminary data about key aspects of the coronavirus without much context can have tremendous negative impact on how the public and policy makers respond to the pandemic," the statement warned.
A study published in April suggested that people who have the new coronavirus are most infectious about two days before symptoms appear, and estimated that 44% of new infections are a result of transmission from people without symptoms, The Times reported.
Calif. Health Official Who Ordered Mandatory Use of Masks Resigns After Threats, Protests
The chief medical officer of Orange County, California resigned Monday due to threats and protests at her home after she issued an order requiring people to wear face coverings in public as many stores and restaurants reopen.
Dr. Nichole Quick issued the order on May 23. Previously, masks were only required for employees who had contact with the public, CBS News reported.
"(Face coverings) can help prevent the transmission of COVID-19. There is evidence to support that and I feel strongly we need a face-covering order in place as we continue to send people out into more social interactions," Quick said.
Severe backlash after the order was issued led to increased security for Quick, CBS News reported.
She didn't make a public comment after her resignation on Monday night.
Quick apparently resigned because the backlash "was too much for her. She has three young children and she's been severely criticized by people who came out demanding her resignation, demonstrations in front of her home," according to Supervisor Doug Chaffee, CBS News reported.
New Coronavirus Introduced to California Several Different Times: Study
The new coronavirus appears to have arrived in California several different times, new genetic research suggests.
"We found out that there have been multiple introductions into California of different lineages of the virus," study leader Dr. Charles Chiu, professor of laboratory medicine at the University of California, San Francisco, told CNN.
In the first few weeks after the new coronavirus first appeared in the United States, it wasn't spreading freely across California, but was introduced in a number of separate incidents, according to the study published in the journal Science.
"It shows that there were several different sparks landing in Northern California, many of which fizzled out probably due to a combination of public health measures and luck," evolutionary biologist Michael Worobey, who was not involved in the study, told CNN.
For the study, Chiu and colleagues analyzed the genomes of the new coronavirus that infected 36 people in nine California counties.
One finding was that an outbreak that infected more than 700 people on the Diamond Princess cruise ship in February most likely originated with one passenger who carried a strain that circulated widely in Washington state and elsewhere, Chiu told CNN.
Another outbreak in Solano County was limited to three people -- a patient and two healthcare workers who cared for her. Contact tracing and quick isolation of the new cases prevented further spread, according to Chiu.
Even though it's a small study, it helps show how a few cases can turn into a pandemic, and how rapid response can stop the spread, Chiu told CNN.