Everything We Know About COVID Booster Shots, Side Effects

Johnson & Johnson released a new update on the potential for a booster shot of its single-dose coronavirus vaccine Tuesday, but as booster shots continue to be debated nationwide, what's next for all three COVID vaccines currently being administered in the U.S.?

Pfizer, Moderna and J&J have each conducted studies surrounding booster doses of their vaccines.

The World Health Organization has strongly objected to rich nations giving a third round of shots when poor countries don’t have enough vaccine for their first. Still, the Biden administration has said it plans to dispense COVID-19 booster shots to most Americans.

In a new weekly series, "COVID Q&A," NBC10 Boston asked three top Boston doctors on Tuesday for their thoughts on COVID vaccine boosters, including whether they're safe, potential side effects, and what the rollout could look like here in Massachusetts.

Here's what we learned:

Do I need a COVID booster shot?

"What we're really seeing with the J&J results is that although one dose is effective, two doses is better," said Dr. Daniel Kuritzkes, chief of Brigham and Women’s Hospital's infectious diseases division. "There was always a question about whether a single dose would be efficient. With a second dose, they got better protection than what was reported after a single dose. That has always been planned as a study."

"Once you've finished a vaccine series, when do you need to remind the immune system about what it previously saw? There's still some controversy about who needs a booster, when should they get boosted and how much of an impact will boosting have as opposed to making sure everyone else who's not vaccinated gets one."

"Ultimately, probably everyone will benefit from a booster dose of mRNA vaccines," added Dr. Shira Doron of Tufts Medical Center.

An FDA advisory committee rejected a plan Friday that would have permitted third doses of the Pfizer vaccine for all Americans 16 and older, voicing reservations over insufficient data and the risk of myocarditis. But the committee subsequently voted unanimously to approve boosters for the medically vulnerable and anyone 65 and over.

Doron said she agrees with the FDA that it's "too early" to recommend boosters as a blanket for all age groups and all age-eligible individuals at this time. Especially since the best way to get the pandemic under control is to focus on people who have not been vaccinated.

"We really need to put our resources into that," she said.

Will the booster shot have side effects? Are there any risks?

Boston Medical Center's Dr. Davidson Hamer said while boosters are important for maintaining and providing long-term immunity, more data is still needed on the efficacy of long-term protection and protection against severe disease for all the vaccines.

But he stressed that booster shots are safe, effective, and are unlikely to result in side effects like the initial doses.

"We've now vaccinated hundreds of millions with messenger RNA vaccines. We have a lot of safety data collected," Hamer said. "Giving a booster for most vaccines is unlikely to result in new side effects being identified... I don't anticipate any safety issues coming out as we start giving boosters."

"I completely agree," added Kuritzkes. "People need to understand there is going to be discussion. There are differences of opinion in certain aspects of how the data gets interpreted. But it shouldn't be taken in any way that there is any doubt about the efficacy and safety of these vaccines. It's all about when do we know people absolutely need to be boosted and how can we best use the vaccines we have to maximize protection for everybody, and what are the best strategies. That's where there is debate. It's not about efficacy. Simply because a booster is needed now or in the future in no way undermines the vaccine as an extraordinary tool in preventing COVID-19."

What will the booster shot rollout look like in Massachusetts?

What the rollout of the vaccine boosters will look like here in Massachusetts and across the country is not yet known.

"We are waiting for official FDA approval and then the CDC advisory council's recommendations on really what that rollout should look like," Doron said. "They haven't defined that. It's up to the CDC's council to get into the nitty gritty. Those over 65 and with underlying medical conditions should be thinking about the fact that they could benefit from a booster and wait for guidance from the CDC and the rollout from the state."

"They should reach out to their doctor after those recommendations are issued to find out if they qualify," she added.

Will I need a booster shot for the Moderna or Johnson & Johnson vaccines?

The other challenge, Hamer said, is that right now the FDA and CDC are only looking at Pfizer's booster vaccine.

"If you've had Moderna or the Jansen/Johnson & Johnson, all this discussion doesn't apply yet," he said. "So it's going to be a little bit confusing on how to move forward, at least for the time being. I think that will change."

Doron said she hopes the CDC addresses that question in their hearings this week. The CDC is scheduled to begin a two-day series of meetings on third doses Wednesday and Thursday.

"I think they will," she said. "If you received Moderna or J&J, wait for additional guidance."

When can eligible people get their third dose?

There has been some talk about booster shots being available by next month, and Kuritzkes said that timeline sounds reasonable.

"I would expect we'd see a series of rolling recommendations following a parallel timeframe in which the original vaccines got approved," he said. "That's more of a regulatory issue. They can only act on the data they have before them. It'll probably be another month, I would guess."

If I got the Moderna or J&J vaccine, can I get a booster shot of Pfizer?

One question that remains unanswered is whether people who received a first dose of Johnson & Johnson can get a Pfizer or Moderna booster, or vice versa.

"That's a question that's been looked at to some extent in the U.K.," Hamer said. "AstraZeneca was followed by Pfizer and has shown fairly robust immune response. The vaccine works in slightly different ways. We need more evidence, although the initial evidence shows that approach is safe."