Even after the rollout of the first coronavirus vaccine, much about COVID-19 vaccines is unknown. Dr. Leonard Krilov, an infectious disease specialist and chief of pediatrics at NYU Langone Hospital-Long Island, explains to Newsday how New Yorkers aren't out of the woods yet. Credit: Debbie Egan-Chin

When vaccinations against the coronavirus began Monday with the first of multiple vaccines in the works, some called it the beginning of the end of the pandemic.

But there are many unknowns about the vaccines, including how long they provide protection and whether they stop a person from spreading the virus. Experts warn that even with vaccines, it will be many months before lifestyles return to something approaching normal — and that’s only if a large majority of the public gets vaccinated, a big "if," because polls show widespread hesitancy to taking a vaccine.

"To be able to say we’re really through this, I think we have at least a year ahead of us," said Dr. Leonard Krilov, an infectious disease specialist and chief of pediatrics at NYU Langone Hospital-Long Island in Mineola.

The U.S. Food and Drug Administration on Dec. 11 gave emergency use authorization for a vaccine from Pfizer and BioNTech, and on Friday the FDA did so for a vaccine from Moderna and the National Institutes of Health. An independent advisory committee of experts endorsed both. Other vaccine candidates are in the pipeline.

Polls over the summer found that only about half of Americans would get a coronavirus vaccine. But attitudes have been changing, surveys show. A poll released Tuesday by the Kaiser Family Foundation found that 71% of Americans would definitely or probably get a vaccine if it’s free and scientists determine it to be safe — up from 63% in September.

That 71% is still at the lower edge of what experts say is necessary to achieve herd immunity. That’s when so many people are immune to a virus that it becomes unlikely that a person will infect someone else.

"It runs out of fuel and there are not enough people to continue to spread it, and [then] it will die down," said Dr. Bruce Farber, chief of infectious diseases at North Shore University Hospital in Manhasset and Long Island Jewish Medical Center in New Hyde Park.

For example, said Dr. Alan Bulbin, director of infectious diseases at St. Francis Hospital in Flower Hill, "If 80% of the population is immune, that means four out of five people who come into contact with the virus, through somebody out there who is potentially infectious, they’re not going to get [sick]. And then they’re potentially not going to spread it to somebody who isn’t immune."

The level needed to achieve herd immunity for COVID-19 is unknown, and projections vary.

"We’ve only known about coronavirus since December," said Danielle Ompad, an associate professor of epidemiology at New York University in Manhattan. "The studies needed to estimate herd immunity are still being conducted."

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said it likely would be 75% to 85%.

The number won’t be known for certain until a few months after herd immunity is achieved, because only then will it be clear if the virus’ spread was largely stopped, Krilov said.

Until then, masks, social distancing and other preventative measures will remain critical, Farber said.

"Months after we reach and continue to have herd immunity is when the virus really will start going away," he said.

Even then, it likely won’t be completely eradicated, Ompad said. Smallpox is the only infectious disease that was eradicated, she said, and even if coronavirus transmission stops among humans, it still may be present among animals, meaning it could end up in people again. Some scientists theorize that bats were the origin of the coronavirus in humans.

One reason masks and social distancing are still necessary for people who are vaccinated is that it is unknown if some vaccinated people have contracted the virus.

"It’s unclear right now whether the vaccine prevents infection or it just prevents illness," Ompad said.

Farber, who reviewed Pfizer-BioNTech vaccine data as one of the seven members of the state’s clinical advisory task force, said people in the clinical trials who got symptoms of COVID-19 were tested for the coronavirus. But those without symptoms were not tested, so it’s possible that some people who were vaccinated and didn’t get sick contracted the virus and were contagious, he said.

Even so, he said, "The vaccine was so effective in preventing people from getting any signs or symptoms that I think that means it’s very unlikely that [vaccinated] people have asymptomatic COVID and are spreading it around."

Although the Pfizer-BioNTech and Moderna vaccines were more effective in clinical trials than many scientists had predicted, they didn’t keep everyone from getting sick. Pfizer-BioNTech’s vaccine had a 95% effectiveness, and Moderna’s had just over 94%, meaning that the rest got ill.

Yet no one who received the Moderna vaccine got seriously sick, and only one person who took the Pfizer-BioNTech vaccine got seriously ill, and that person didn’t require hospitalization and recovered quickly, Farber said. That demonstrates that even when the vaccines didn’t completely prevent illness, they ameliorated the symptoms, he said.

At least three people have had severe allergic reactions after taking the Pfizer-BioNTech vaccine, including a health worker in Alaska and two health care employees in Britain.

Onisis Stefas, chief pharmacy officer for New Hyde Park-based Northwell Health, said other vaccines also cause allergic reactions. "Anything that you ingest in your body or even use topically, you can get a reaction to," he said.

For those who are immune from getting sick with COVID-19, it’s not clear how long protection will last. That will only be known with time, as those who are vaccinated are followed, Bulbin said.

"When you see such striking numbers upfront, the scientific optimism would suggest this is going to be long-lasting," Bulbin said. "How this plays out, we’ll see."

With Cecilia Dowd, AP

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