The highly contagious delta variant is the fastest and fittest coronavirus strain that will “pick off” the most vulnerable people, the U.N. health agency said.

“Delta has the potential “to be more lethal because it’s more efficient in the way it transmits between humans,” the world health Organization (WHO)’s Dr. Mike Ryan said, according to CNBS.

The highly contagious delta variant is the fastest and fittest coronavirus strain yet, and it will “pick off” the most vulnerable people, especially in places with low Covid-19 vaccination rates, World Health Organization officials warned Monday.

Delta, first identified in India, has the potential “to be more lethal because it’s more efficient in the way it transmits between humans and it will eventually find those vulnerable individuals who will become severely ill, have to be hospitalized and potentially die,” Dr. Mike Ryan, executive director of the WHO’s health emergencies program, said during a news conference.

Ryan said world leaders and public health officials can help defend the most vulnerable through the donation and distribution of COVID vaccines.

“We can protect those vulnerable people, those front-line workers,” Ryan said.  

The WHO said Friday that delta is becoming the dominant variant of the disease worldwide.

The U.N. health agency declared delta a “variant of concern” last month. A variant can be labeled as “of concern” if it has been shown to be more contagious, more deadly or more resistant to current vaccines and treatments, according to the health organization.

Delta is now replacing alpha, the highly contagious variant that swept across Europe and later the U.S. earlier this year, Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, said in a recent interview.

Studies reportedly suggest it is around 60% more transmissible than alpha, which was more contagious than the original strain that emerged from Wuhan, China, in late 2019.

“We need to vaccinate now. Get everyone vaccinated now,” Offit said.

Delta has now spread to 92 countries, Maria Van Kerkhove, the WHO’s technical lead for COVID, said Monday.  It now makes up at least 10% of all new cases in the United States, according to the Centers for Disease Control and Prevention, and is on its way to becoming the dominant variant in the nation.

In Moscow, delta reportedly makes up almost 90 percent of all new COVID cases.

WHO officials have said there were reports that the delta variant also causes more severe symptoms, but that more research is needed to confirm those conclusions.  Still, there are signs the delta strain could provoke different symptoms than other variants.

The WHO has been urging wealthy nations, including the U.S. to donate doses. The Biden administration earlier Monday detailed where it will send 55 million vaccine doses, the majority of which will be distributed through COVAX, the WHO-backed immunization program.