People wearing masks are seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

People wearing masks are seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

A boy wearing a mask is seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

People wearing masks are seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

People wearing masks are seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

People wearing masks are seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

People wearing masks are seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

People wearing masks are seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

A man wearing a mask is seen outside a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

A man wearing a mask is seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)

A woman wearing a mask is seen in a shopping mall in San Mateo, California, the United States, May 19, 2021. California's public health officials said Monday the most populous state of the United States would not "implement the CDC guidelines that allow fully vaccinated people to go without a mask in most situations" before June 15. (Photo: Xinhua)