Since vaccines emerged as the primary tool to fight the COVID-19 pandemic, there has been uncertainly about how much protection the vaccines will provide and, just as importantly, for how long.

Some Mainers who were first in line now have been fully vaccinated for close to six months. Do they need to start thinking about getting a booster or a new vaccine anytime soon? Flu shots, after all, are offered once a year. Is that where things are headed with coronavirus?

Researchers are still studying this question, and many more, but the short answer at the moment is: No one knows for sure.

“It is still too scientifically early to know whether any series of vaccines will be needed in the fall or winter, or at all,” said Dr. Nirav Shah, director of the Maine Center for Disease Control and Prevention. “But I do believe it is prudent for folks to start thinking about what it could mean for them or their family.”

So, with the caveat that things could – and probably will – change, here is the latest thinking on the future of COVID-19 vaccines.

How do these vaccines work again?

The Pfizer and Moderna vaccines were developed using mRNA technology, which delivers a piece of genetic code from the coronavirus to host cells in the body. That code gives cells instructions for making copies of spike proteins, which stimulate an immune response that produces antibodies and develops memory cells to recognize and respond if the body is infected with the actual virus.

The Johnson & Johnson version is what’s known as a carrier vaccine, a more traditional type of vaccine that involves injecting an inactive adenovirus (a common virus) as a shell to carry genetic code on the spike proteins to cells in the body. The body’s immune system then creates antibodies and memory cells to protect against an actual infection.

What is a booster shot? How is that different from a new vaccine?

A booster shot is a shot of the same vaccine given some time after the first course to fortify protection against an original infection.

Tetanus shots, for instance, are recommended every 10 years. That’s a booster.

Flu shots, on the other hand, are not boosters. Each year, a new vaccine is developed to protect against what experts believe are the most dominant strains of any given season.

“Sometimes they get it right, sometimes they are off,” said Josh Michaud, associate director for Global Health Policy at the Kaiser Family Foundation. “The flu virus is particularly good at mutating and changing, but we’ve learned the coronavirus doesn’t behave the same way as the flu.”

Shah said that whether it’s a booster shot or a new vaccine, the end result is the same for patients: another shot.

So, will we need booster shots?

Maybe.

“The best guess is that we will need boosters, particularly for those that have immune issues,” Michaud said. “But the question is: How long before they are needed?”

The real-world studies, dating to clinical trials last year, are only about a year old. Research has emerged that suggests protection remains strong after a year, but more time is needed to see if that protection wanes. The National Institutes of Health has begun a clinical trial of fully vaccinated individuals to see whether a booster of the Moderna shot will increase their antibodies and prolong protection against getting infected with the virus.

Not everyone agrees.

“I don’t think we need boosters,” said Dr. Kawsar Talaat, an infectious disease expert and faculty member at the Johns Hopkins University Bloomberg School of Public Health. “The data from these vaccines is they provide excellent protection.”

“It’s not just creating antibodies, it’s about memory,” she added. “These vaccines create very strong immune memory.”

What does that mean?

According to Shah, the body’s immune system works in two major ways to fight off something that is foreign or unwelcome, like a virus. The first is to develop antibodies, which are proteins made by B cells within the body that “neutralize the invader,” Shah said. The second immune response comes from T cells, which actively attack the antigens by binding to and killing infected cells.

The major question, Shah said, is to what extent B cells in the body will remember a virus that has been in the body years ago.

For instance, if vaccines stimulate B cells to keep COVID-19 from causing serious illness, will those same B cells activate if coronavirus is introduced down the road?

All pathogens are different. For instance, if someone gets measles, or is vaccinated against measles, they are likely protected for life without needing another vaccine or booster.

So, will we need a new vaccine at some point?

Possibly, but the big question mark is variants.

By now, many coronavirus variants have been identified, some of which have proven to be more transmissible and more serious. However, the vaccines that have been approved in the United States – by Pfizer, Moderna and Johnson & Johnson – all appear to offer strong protection against those variants.

The unknown, of course, is whether a variant will develop that is vaccine resistant. The risk is not insignificant since much of the world remains unvaccinated.

Talaat said the best thing the U.S. can do is “stop worrying about boosters and worry about vaccines getting everywhere in the world.” The likelihood for boosters will be significantly lessened if the virus fizzles out across the globe and doesn’t have a chance to mutate further.

Shah said he understands if people might have more questions.

“They might say, ‘Wait, you said this vaccine was so good, now we have to get one in the fall, what’s up with that?’” he said.

But because the vaccines already have been developed, they are very “malleable scientifically,” Shah said. In other words, if a new vaccine needs to be developed to address a particular variant, that can happen quickly.

How will we know if additional vaccines are needed?

“People who are vaccinated will start getting infected,” Talaat said. “That’s why tracking breakthrough infections is important.”

Even more than that, experts will monitor people who are getting sick to determine what strains, or variants, are causing severe infections. That’s already happening in some places, like nursing homes, which are often among the first places that are susceptible to new outbreaks of vaccine-resistant variants.

Another way is to monitor antibody levels of those who have been vaccinated. If those antibody levels drop off after a certain amount of time, that could be a sign that a booster is needed, although antibodies are only half of the equation, as noted above.

Shah said that although monitoring breakthrough cases is important, the real-world efficacy studies already underway offer a more complete picture.

So far, he said, “It looks pretty darn good.”

If booster or new vaccines are needed, will they be rolled out in the same way?

Shah stressed that any decision about next steps is not his to make, saying that the Maine CDC and other stakeholders have started to plan.

“I’m obligated to say that the best way to avoid the need for this is for everyone to go and get vaccinated,” he said.

But if boosters or new vaccines are needed, Shah said the rollout is likely to look different.

“If we do need a second series … the urgency will not be the same,” he explained.

In all likelihood, individuals may be encouraged to get another shot at the same time they get a flu shot, which means more vaccinations would happen at pharmacies and doctor’s offices.

Still, if mass clinics are needed again, Shah said the state could easily mobilize.

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