By Betty Yu

SAN FRANCISCO (CBS SF) — The FDA granted emergency use approval for Johnson & Johnson’s COVID-19 vaccine Saturday, making it the third vaccine in the nation’s war against the virus.

Experts say one of the advantages of the vaccine is that it works with just one dose instead of two.

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Johnson & Johnson said shipments to states including California could begin as early as Monday.

By the end of next month, the company expects to deliver 20 million doses to the U.S., and 100 million by summer.

“The bottom line is that the more vaccines that have high efficacy that we can get into play, the better there is,” said Dr. Anthony Fauci.

Johnson & Johnson’s vaccine showed 85% efficacy against severe illness, and 100% protection against COVID-19 deaths 28 days after getting the shot.

UCSF infectious disease expert Dr. Monica Gandhi says we’re already seeing effects of the vaccine in communities.

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“I think vaccination is playing a role in our decreasing cases and hospitalizations not only across the U.S., but in California, because California, we had a sluggish start, but we do have 25% of our population vaccinated at this point, we do see a sharpness to the decline,” said Dr. Gandhi.

Another benefit of the vaccine is that it can be stored in a regular refrigerator.

Its arrival is happening as several virus variants are spreading.

“I think if there’s going to be a problem with the variants, it’s going to be that we’re going to see a little burst of transmission and outbreaks here and there,” said UCSF epidemiologist Dr. George Rutherford. “And that’s when the Johnson & Johnson vaccine becomes really helpful, because you can go and vaccinate around those, try to limit the spread. Not only through contact tracing and isolation, but by going out to the next layer around and vaccinating around them.”

Meanwile, Pfizer and Moderna expect their shipments to double or possibly triple in the coming weeks.

“We’re not moving as fast as the UK and Israel, or United Arab Emirates, or other places, on the other hand, they keep on telling us, and I think this is true, that the doses are going to increase in March,” said Dr. Gandhi.

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Gov. Gavin Newsom said Friday that the state expects to receive some 380,000 Johnson & Johnson doses next week.