Viewers have told NewsCenter 5 that it can be difficult to keep up with the frequent developments regarding the COVID-19 vaccine.With that in mind, NewsCenter 5 has decided to break down the latest information on each of the three vaccines available in the United States: Pfizer-BioNTech, Moderna and Johnson & Johnson (Janssen).Most people who have received a COVID-19 vaccine in Massachusetts got the Pfizer vaccine. More than 2.5 million people in the Bay State got the Pfizer shot, a figure that accounts for about 56% of all vaccines administered in the state.Currently, Pfizer’s COVID-19 vaccine is the only one available that has received full approval from the U.S. Food and Drug Administration and is the only one that can be administered to children as young as 12 years old.In addition, Pfizer’s COVID-19 booster shot has been approved by the FDA and the U.S. Centers for Disease Control and Prevention for the following at-risk groups of people who received both doses of the Pfizer vaccine at least six months ago:People age 65 and olderPeople age 18 to 64 who have an underlying medical conditionPeople age 18 to 64 whose occupation or residence put them at higher risk of exposure to the coronavirus “People can go out and get that, especially if they’re over 65 or if they’re an adult with chronic conditions,” said Dr. Todd Ellerin, the director of infectious diseases for South Shore Health.Nearly 1.7 million Massachusetts residents have received the Moderna COVID-19 vaccine, which accounts for nearly 37% of vaccines administered in the state.Like Pfizer’s vaccine, the Moderna vaccine requires two doses for full vaccination and uses mRNA technology.Immunocompromised people who received both doses of Moderna’s COVID-19 vaccine are currently eligible to receive a booster, according to the CDC.Everyone else who received a Moderna vaccine must wait for the FDA to review the Cambridge-based company’s application, which was filed Sept. 1, before they can receive a booster.”We have to learn whether the dosage is going to be the same dosage as the primary series or whether it’s going to be a half-dose, as Moderna has been saying,” Ellerin said. “Again, we have to wait for that data to be reviewed by the FDA and the CDC, and then it likely will get the green light, just as Pfizer’s did.”When it comes to Johnson & Johnson, more than 309,000 people received that COVID-19 vaccine in Massachusetts, making up the smallest percentage of administered vaccines in the state at 6.7%. The Johnson & Johnson COVID-19 vaccine is the only single-dose vaccine available in the U.S., receiving emergency-use authorization from the FDA about 10 weeks later than the Pfizer and Moderna vaccines.The J&J vaccine is also developed differently, using viral vector technology that has been successful since the 1970s.The company recently reported that a two-dose regimen of its vaccine given 56 days apart significantly boosts protection against COVID-19 and antibody levels surge even higher when the second shot is administered eight months after the first. Johnson & Johnson said it has submitted data to the FDA, but until it is reviewed within the next two months, no J&J booster shot will be available.”It’s coming, but it’s likely going to follow Moderna next,” Ellerin said. “Overall, I think we’re really going in a positive direction before winter comes.”The CDC does not recommend one brand of COVID-19 vaccine over another, stating that all three are safe and effective at preventing serious symptoms and death.