LOS ANGELES (KTLA) — With millions of people in Los Angeles County now fully vaccinated against COVID-19, public health officials said Thursday evidence is becoming clearer that the shots provide exceptional protection against sickness and death from the virus.

NewsNation affiliate KTLA reports data on “breakthrough cases,” or people who test positive for coronavirus despite being vaccinated, shows that only 0.00036% of fully vaccinated people went on to die from the virus, Barbara Ferrer, the county’s public health director, said in a news briefing.

Of the nearly 3.3 million fully vaccinated people included in the data, 12 contracted COVID-19 and died, and four of them had severely weakened immune systems, Ferrer said.

“We do already know that people with weak immune systems may not generate adequate protection in response to the vaccine,” she said. “So this finding is a signal to us that people whose immune systems are suppressed may need to continue to take additional steps to protect themselves in seasons and in situations where COVID and other respiratory viruses are spreading more easily.”

A total of 933 people, or about .03%, tested positive for the virus after being fully vaccinated. And 71 of them, or .002%, were hospitalized for those infections, according to the data.

“These numbers show that the vaccine is working extraordinarily well to prevent infection, illness and death in almost everyone vaccinated,” Ferrer said.

She added that the positive tests include those who are asymptomatic with no known exposure, and who are required to test for work or to receive medical care. There’s also likely to be people who received a false positive test result.

Ferrer cited another study done at a hospital in Houston, Texas, that showed 170 of about 23,000 fully vaccinated people were hospitalized with COVID, while 1,700 of about 64,000 unvaccinated people were hospitalized. That’s 0.7% versus 2.7% and yields a vaccine effectiveness rate of about 99%, she said.

“This means that in the real world, in the United States, being fully vaccinated kept nearly 99% of people who would have been hospitalized for COVID out of the hospital,” Ferrer said.

In L.A. County, more than 5 million people have received at least one dose, and 47% of residents 16 and older are fully vaccinated. And since the county began vaccinating their age group last Thursday, 6% of 12- to 15-year-olds have gotten a shot.

While vaccine distribution has slowed, Ferrer expressed “great hope in getting to where we want to be with our younger age groups.” She also said there’s been an uptick in the vaccination rate among some racial groups hardest hit by the pandemic, but disparity remains.

There’s been a relative increase of 136% among 16- and 17-year-olds, 37% among 18- to 29-year-olds, and 27% among 30- to 49-year-olds, who Ferrer said “form the core of L.A. County’s labor force.”

Among Latinx adults the relative increase was 34%, 26% among black adults, and in the low 20s for Native Americans and Asian adults, but the increase was 18% among white adults.

Still, it hasn’t been enough to close the gap among richer, whiter communities and poorer, darker ones, Ferrer said.

“Over these next few weeks as we prepare for our full reopening, we do need to double down on our efforts to reduce any barriers to vaccination in hard-hit communities,” she said.

The health director says infections, hospitalizations and deaths continue to see “very small” declines, something she called “welcome news.” The county reported 19 additional deaths and 245 new cases Thursday.

“One reason why transmission is so low in L.A. County is because the vaccines are powerful and effective,” Ferrer said.

But variants continue to pose a threat to the unvaccinated, and the UK variant has overtaken the homegrown California one in the county. Among positive tests sampled last week, 53% were the UK variant, none were the California variant, and six were the Brazil variant, Ferrer said.

“Recent research findings provide added evidence that our currently available vaccines appear to be highly effective against the variants of concern that are circulating here now,” she added.