Los Angeles County’s health director on Thursday stressed the importance of ramping up vaccination efforts, saying the Delta coronavirus variant being blamed for massive outbreaks in India has been detected in the county since in April.

The variant is already circulating in the U.S. and several of other countries, and it’s not yet clear whether it makes people sicker.

“But what does seem clear is that among unvaccinated people, Delta variants are spreading with great speed,” L.A. County Health Director Barbara Ferrer said.

Current COVID-19 vaccines have been shown to be effective against the Delta variant, but not as much for people who took only one shot of a two-dose vaccine.

Dr. Anthony Fauci, the nation’s leading infectious disease expert, said data from Britain’s public health agency shows that two doses of the Pfizer vaccine were 88% effective in preventing symptomatic disease caused by Delta. But one dose offers just 33% protection, the Washington Post reported.

“This increases our urgency to fully vaccinate as many people as possible,” Ferrer said.

The county’s public health lab has identified nine cases of the Delta variants, according to the health director.

“We started seeing small numbers of these cases among L.A. County residents in early April, and we’re not yet seeing an appreciable increase in the number of Delta or Kappa variants among the sample sequenced from our residents, and this is good news,” Ferrer said, attributing the small number to the county’s low virus transmission rates.

The most common variant of concern circulating in L.A. County is still the Alpha variant, which was first detected in the United Kingdom, according to the health department.

The Delta variant has also been exploding in Britain, raising fears for another virus wave in the country.

Experts told the Los Angeles Times that the U.S. is likely in better shape to ward off the variant among young people than the U.K. since vaccines are more available.

“Keeping this variant from spreading in our county requires continued effort to get immunizations to unvaccinated residents in our communities, and to urge residents to keep taking measures to protect themselves and others,” Ferrer said. “This is particularly important for those who are not vaccinated, who can end up unknowingly being incubators for Delta variants, and other variants of concern.”