(CNN) Before vaccines, the San Francisco Department of Public Health needed three whiteboards to capture all the names of senior facilities that had Covid-19 outbreaks.
"We had been dealing with outbreaks the whole time. Everywhere, at a ton of facilities, big, small, rich, poor, it didn't matter," said Dr. Louise Aronson,a professor with the UCSF Division of Geriatrics.
But by February, when seniors were starting to get vaccinated in greater numbers, the department started to erase names from these outbreak lists.
"I think it was April when all the whiteboards were empty. I took a picture of it with my phone. It was so quick. The vaccines were transformational," Aronson told CNN.
"It was sort of a very visible miracle."
These "visible miracles" were playing out across the country this spring, according to a new report published Tuesday by the US Department of Health and Human Services.
Vaccinations prevented at least a quarter of a million Covid-19 infections among seniors and tens of thousands of deaths just between January and May of this year.
The report from researchers at HHS's Office of the Assistant Secretary for Planning and Evaluation found that vaccinations of Medicare beneficiaries were linked to a reduction in about 265,000 new Covid-19 infections, 107,000 hospitalizations, and 39,000 deaths in that time period.
Seniors have been hit hard by the pandemic. Nearly 80% of Covid-19 deaths have been among people 65 and older. These numbers show why public health leaders have been pushing so hard to get people vaccinated.
"The fact that you were able to stop that many deaths and that many cases and hospitalizations even that early on, just a few months into when people could get vaccinated, that really goes to show you that the vaccine works," Dr. Claudia Hoyen, who did not work on this study, told CNN. She is an infectious disease specialist and director of pediatric infection control at UH Rainbow Babies and Children's Hospital in Cleveland.
The US Centers for Disease Control and Prevention said people 65 and older who are fully vaccinated saw a 94% reduced risk of hospitalization.
Seniors are now the most vaccinated demographic in the US. More than 94% of seniors now have gotten at least one dose of the Covid-19 vaccine, according to the CDC. Even in Alabama where vaccine uptake is slow, seniors are the most vaccinated of any age group, according to the Alabama Public Health Department.
When all adults had high vaccination rates in an area, not just seniors, protection was even better.
The positive impact the vaccines had were seen across all racial and ethnic groups and across all 48 states where research was available. HHS estimates there was a reduction of 29,000 infections and nearly 4,600 deaths among Black Medicare beneficiaries and a similar number among Hispanic beneficiaries. For people who identify as Asian, it was a reduction of 7,600 infections and 1,400 deaths.
Vaccinations made the biggest difference averting deaths and hospitalizations among Alaska Native and American Indian communities, the report found, with an estimated 21% reduction in infections, compared to 18% among White populations, and a 25% reduction in the number of deaths compared to 22% among White people.
"This report reaffirms what we hear routinely from states: COVID-19 vaccines save lives, prevent hospitalizations, and reduce infection," HHS Secretary Xavier Becerra said in a statement. "The Biden-Harris Administration has prioritized getting vaccines quickly to pharmacies, nursing homes, doctors' offices and even provided increased reimbursement rates for at-home COVID-19 vaccinations, so that seniors and others can easily get vaccinated."
Due to waning immunity, the CDC now recommends that people 65 and older get a booster at least six months after their primary series if they got the Pfizer-BioNTech shots. About 8% of people 65 and older already have.
Vaccine advisers to the US Food and Drug Administration are scheduled to discuss booster doses for the Moderna and Johnson & Johnson vaccines later this month.
"I hope this makes a lot of seniors really excited about the news that they are now eligible for boosters if they're six months out," Hoyen said. "And as we're going into winter we want to be sure that everyone's immunity is up, so now would also be a good time for those seniors to go ahead and think about boosters and flu shots."