The World Health Organization has issued an emergency alert for the Zika outbreak, warning that many people are vulnerable to the virus and are unlikely to be protected from it.

The WHO said the outbreak has affected 2.2 million people in the Americas and 2.1 million in Latin America.

It has been linked to microcephaly in newborns, severe birth defects, birth defects in adults and a spike in deaths.WHO Director-General Margaret Chan said Tuesday that the virus poses a “very real and imminent threat to public health.”

The agency said that in a two-week period from July 1 to Aug. 31, there were more than 50,000 confirmed cases of Zika in Puerto Rico, Puerto Rico and the U.S. Virgin Islands.

WHO also said that about 1,800 new cases of the virus were confirmed in Puerto Rican hospitals and 1,700 in Puerto Ricans.

The agency said it is continuing to monitor the virus in other countries, including Brazil, Argentina, Mexico and Colombia.

The new infections in Puerto Rica and the Dominican Republic are the most recent Zika cases to be confirmed in the U, as well as the first cases of infection in the continental U.K., WHO said.

The virus was first identified in Brazil in March, and has since spread across the region, including in the Caribbean and U.N. member states.

The CDC estimates that roughly 2 million people worldwide are at risk of contracting Zika.

That includes 3.2 billion people in Latin American and the Caribbean, and about 2.5 million people who live in the United States, according to WHO.WHO said there is little or no information on how many people have died from Zika, but the virus has been blamed for many cases of microcephi in babies.

The agency’s warning comes as scientists are investigating how Zika affects unborn babies and how long they may live.

WHO said it will publish a report on Zika in the coming days.