Gov. Kathy Hochul is encouraging all vaccinated New Yorkers to get COVID-19 booster shots -- after the Food and Drug Administration authorized the additional doses Friday morning.

"The vaccine is safe, free and the best way to prevent the spread of this deadly virus in our communities as we head into the colder months,” Hochul said in a statement. “If you want to protect yourself and loved ones from COVID-19, get the vaccine. If you are vaccinated already, get the booster."

A CDC advisory panel voted unanimously Friday afternoon in favor of giving third shots to Pfizer and Moderna recipients older than 18. But it issued two recommendations, which differ by age group.

Stronger language was used in the recommendation for everyone older than 50 as well as anyone over 18 living in a long-term care facility. They "should" get a booster shot.

All others over 18 received a lighter recommendation -- they "may" get the shot if they feel at high-risk.

The difference centers around the fact that most people under 50 are still almost fully protected against severe COVID with their original two doses of the Pfizer and Moderna vaccines. All adult recipients of the single-shot Johnson & Johnson vaccine are still advised to get a booster shot after two months.

CDC director Dr. Rochelle Walensky accepted the new guidance by late Friday afternoon, finalizing the expansion of booster shots. The change makes the shots available at federally-run pharmacy sites.

And it will likely clear up confusion surrounding boosters for New York residents living outside of the five boroughs, after New York City officials trailblazed and expanded access earlier in the week.

Here’s what all New Yorkers should know about the rules and science around boosters.

How New York City Stepped Ahead

Before today, federal rules permitted boosters only to vulnerable groups, including those older than 65 as well as people living and working in high-risk settings.

On Monday, New York City used the latter rule to make boosters available for all vaccinated adults, circumventing state rules that mimicked federal policy. Under the old criteria, city health officials argued, all New York City residents could qualify for boosters given community transmission rates and each borough’s high-density population.

“I view all New Yorkers because of the density of our city of being at higher risk,” said Dr. Mitchell Katz, the head of the city’s public hospital system during the City Hall announcement.

Under Monday's guidance from the city’s health commissioner Dr. Dave Chokshi, all vaccine providers in the city were instructed to let patients determine their own level of risk and that no one should be turned away while seeking boosters.

“We want you to get a booster now,” Mayor Bill de Blasio later said. “And the city is making clear, we're prepared to serve everyone. It is important. It's timely.”

The Pharmacy Conundrum

This was where things became tricky, and the city’s loophole bred some confusion. Many people could successfully get a booster, while others were turned away. Federally-supported pharmacies were technically prohibited from giving the boosters, while city-run sites and private providers could.

Even in New York City, news reports documented hurdles for some in getting boosters as pharmacy chains continued to adhere to the strict federal guidelines and asked individuals to provide proof of their risk category. Not long after, the state’s Department of Health site took a page from New York City by inserting language that encouraged those who “feel at risk” to seek a booster shot. The updated language said, “Individuals who have questions about their risk are encouraged to consult with their primary health care providers.”

With the formal authorization from FDA and CDC, federal, state and city health officials will finally all be on the same page once the New York State Department of Health issues its interpretation of the federal guidelines.

Do I Really Need That Third Shot?

Evidence suggests that antibodies against the coronavirus ultimately wane, meaning everyone might become more prone to infection over time. That pattern is most pronounced in older and immunocompromised adults who have weaker immune systems in general, and it also leaves them more susceptible to severe illness.

But experts have been divided on whether boosters are necessary for healthy, younger adults because the original course of vaccine still lowers the chances of severe disease in this group by more than 90%. The original dosing still provides a profound public health impact, which was part of the original reason for delaying the federal authorization to all adults earlier this autumn.

Dr. Denis Nash, an epidemiology professor at the City University of New York, told Gothamist that from a public health standpoint, increasing first doses “has to be the main focus and goal of public health.” As of Friday, nearly 88% of New York City adults had received at least one dose, but citywide coverage for all ages is only 74%. That means more than 2.1 million New Yorkers -- mostly kids -- remain unvaccinated.

But given the anticipated CDC decision, those in favor of broadening access to boosters appear to be on the cusp of winning the policy fight. Dr. Anthony Fauci, the top COVID-19 adviser to President Biden, has in recent days publicly urged all vaccinated adults to get boosters. During a health policy summit, he described boosters as essential going forward. “A booster is part of what the original regimen should be,” he said, according to ABC News.

In New York City and other parts of the country, health officials have also expressed concerns about a potential COVID-19 surge during the colder months and holidays, when more people are expected to gather indoors.

On Wednesday, de Blasio and health officials urged all New Yorkers, regardless of vaccination status, to get tested before traveling and gathering with others for the holidays.

Appearing on The Brian Lehrer Show on Friday, Dr. Daniel Griffin, an infectious disease specialist at Columbia University, stressed the importance of getting tested before and after large family gatherings.

“My motto is never miss an opportunity to test,” Griffin said. “Vaccinated people are less likely to spread, but they can.”

This story has been updated with the CDC Director's decision to expand booster access.