By Betty Yu

SAN FRANCISCO (CBS SF) — Johnson & Johnson says its vaccine will either prevent you from getting COVID, or if you have it, it would be a much milder case. The company plans to get emergency authorization in the U.S. within a week, and supply 100 million doses by June.

It’s first one-shot COVID vaccine and is offering the world a potentially new weapon against the mutating virus. Data shows that the vaccine is 72% effective against moderate and severe COVID-19 in the U.S.

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It’s 85% efficient in preventing serious symptoms in global trials.

“In this moment what are we trying to get to, we are trying to get to herd immunity, we are not trying to get to perfection,” said UCSF Infectious Disease Expert Dr. Monica Gandhi.

Dr. Gandhi says if she had a choice, she would be okay with getting one-dose of the Johnson & Johnson shot.

“There is an efficacy advantage to Moderna and Pfizer, but the one dose, two-dose thing, may end up pushing Johnson & Johnson over with an advantage to get it into people quickly,” she added.

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Dr. Gandhi also said trials are already underway to determine the efficacy of two-doses of the Johnson & Johnson vaccine.

There are concerns over its 57% efficacy rate in South Africa. It’s highly-contagious variant is now in the U.S.

“This is a wake up call,” said Dr. Anthony Fauci. “That we will continue to see the evolution of mutants… So that means that we as a government, the companies, all of us that are in this together, will have to be nimble to be able to just adjust readily to make versions of the vaccine.”

Dr. Fauci said children under 16 could get vaccinated by early summer. Vaccines are not yet approved for children.

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“From my perspective, having seen the serious consequences of disease on both children and adults, for me thinking about that choice, it’s really thinking that it’s a safer way to develop immunity,” said Stanford University School of Medicine Professor of Pediatrics Dr. Grace Lee.