4 people who got COVID-19 booster shots share what it felt like to get an extra vaccine dose

• The US has authorized third doses of Pfizer's COVID-19 vaccine to adults over 65, and others at high risk of developing severe disease.
• Already, more than two million Americans know what it feels like to get a booster shot.
• The side effects, they say, are much like after a second shot, with some arm pain and fatigue.

The federal government is starting to recommend third shots of COVID-19 vaccines to large numbers of vulnerable people living in the US.

Already in August, the US Food and Drug Administration authorized, and the Centers for Disease Control and Prevention recommended, a boost for all immunocompromised people who were vaccinated at least a month prior.

This week, the FDA expanded its booster authorization to a much broader population, and the CDC is now recommending certain adults who've had Pfizer's vaccine get a third shot at least six months after their initial one.

But the truth is that many people have already taken it upon themselves to get boosted, whether they are in priority groups or not. They say their side effects are, by and large, a lot like the ones they had after a second dose of Pfizer or Moderna.

Most are sticking to the same brand, and reporting milder side effects

More than 2.3 million Americans have gotten booster doses already, according to CDC data, a number that most certainly includes people who are not immunocompromised.

"It's not happening randomly," Dr. Ashish Jha, dean of the Brown School of Public Health, told a group of journalists recently, explaining how he had recently been at a dinner where roughly a quarter of attendees had boosted themselves. "It is wealthier people, it is more highly educated people who are going out and getting boosters on their own."

More than 21,900 people have reported their third dose side effects using the CDC's v-safe text messaging system.

Nearly all of them (more than 98%) remain loyal to the same brand when they go back for a third shot (Pfizer recipients boost with Pfizer, Moderna recipients with Moderna.) Some are boosting their single shot of J&J with a second shot of the same, while others are topping it up with a jab of mRNA vaccine from Pfizer or Moderna.

In general, reactions to third doses of the two mRNA vaccines appear quite similar to second doses, though third dose side effects may be slightly milder.

'Out of commission for a day'

Steve Walz, head of international relations at Israel's Sheba Medical Center, spoke to Insider after his third dose of Pfizer. "The only thing that bothered me was I was extremely tired for 24 hours," Walz, who is in his 60s, said. "That's it. I didn't have any of those shakes, fevers, or all the other reactions that most people have. I guess I'm fortunate."

Younger adults told Insider similar stories.

Alec Lynch, who's 21 and on medication that affects his immune system, said he was "just out of commission for a day," laying in bed after he got a third shot of Pfizer in August. Lynch described feeling "tired and achy" and "kind of gross" but without a fever.

32-year-old Andy Sparks who boosted his single shot J&J vaccine with a shot of Moderna said his arm hurt "way worse" after the Moderna boost than with the initial J&J.

Katie Bent, 30, boosted her J&J with Pfizer and said after that second shot she was so tired she slept for 15 hours, whereas with the J&J she was just "a little tired and sore afterwards."

(She cautioned, however, that she's generally "a fairly sleep deprived person," so it's unclear whether that fatigue was all a result of the shot.)

She said it felt like "when you've been sick for a while, and then the fever breaks and you know that you're on the mend."

Arm pain and swelling

By far the most common side effect felt after a third COVID-19 dose is arm pain at the injection site.

Fatigue and other muscle aches (myalgia) are also common in the week after a third mRNA injection.

Data that Pfizer presented to the CDC this week also suggested that more people may have swollen lymph nodes after a third dose of the vaccine than with a first or second, but that is temporary, and only happened about 5% of the time in their trials.

Health officials are not sold on the widespread need for boosters yet

The new CDC recommendations of who should get a Pfizer booster shot include people who:

• are 65 or older
• live in a long term care facility (like a nursing home)
• are 50-64 years old with underlying medical conditions that put them at greater risk of severe COVID-19

The CDC is also suggesting that other adults who've had Pfizer, if they wish, may receive a third shot at least six months after their initial vaccination course if they:

• are 18-49 years old with underlying medical conditions
• or are 18-49 years old and are at increased risk of COVID-19 exposure and transmission "because of occupational or institutional setting" (e.g. healthcare workers, prisoners, and other frontline workers)

The CDC stresses adults under the age of 50 should make their decision about a booster "based on their individual benefits and risks."

Independent advisors to the CDC were torn about recommending booster shots to younger adults who are at higher risk of catching COVID-19 at work, like healthcare workers, frontline workers, and prison guards.

They said that giving out boosters isn't going to end the pandemic. Getting more people vaccinated would help more.

The areas of the country that are hardest hit by the virus, with more hospitalizations and more deaths, are the places where large numbers of people remain without a single shot.