As the coronavirus continues to spread across the country, health officials are encouraging Americans to get booster shots—and some organizations are mandating boosters for their staff and customers.

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Officials, organizations push boosters for booster shots

According to CDC Director Rochelle Walensky, omicron currently makes up 3% of all coronavirus cases in the United States, but this percentage is expected to swiftly grow over the next few weeks—especially as people gather with their families and friends for the holidays.

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Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said booster doses are likely needed to protect against infection from the omicron variant. Early data suggests that two doses of a Covid-19 vaccine are less effective against omicron compared to previous variants.

"The message remains clear," Fauci said. "If you are unvaccinated, get vaccinated, and particularly in the arena of omicron, if you are fully vaccinated, get boosted."

Separately, in a White House briefing, Walensky also encouraged eligible Americans to get vaccinated and boosted. "Vaccination, boosting, and masking are especially critical for those who are most vulnerable," she said.

In addition, several businesses, employers, and organizations have also started mandating Covid-19 booster shots, Axios reports. For example, several universities, including Georgetown University, New York University, and two private colleges in Minnesota, have announced booster requirements for their students and staff. The Metropolitan Opera is also requiring eligible adult employees and audience members to be boosted to enter, and the NFL is requiring its coaches and staff to receive a booster shot by Dec. 27.

Currently, the definition of "fully vaccinated" does not include a booster dose, but some public health experts, including Fauci, said the definition should eventually change to include an additional dose.

"[I]t is going to be a matter of when, not if" the definition of fully vaccinated changes, Fauci said.

What to expect from a booster dose

Individuals who receive a booster shot can expect the side effects to be like those experienced after the initial vaccine doses, according to health experts.

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Data from Pfizer shows that side effects after a booster shot of its Covid-19 vaccine were nearly identical to the side effects after a second dose. These side effects include fatigue, headaches, and muscle pain. However, fewer study participants reported fevers after a booster dose (8.7%) compared with after a second dose (16.4%).

People who received a Moderna booster reported fewer side effects overall compared with after the second dose, which may be because Moderna reduced the dosage of its booster, NPR reports.

However, individuals may be more likely to experience side effects after a booster if they mix and match vaccines instead of using the same brand for all three doses. For instance, a study published in The Lancet found that more people who received a mix of the AstraZeneca and Pfizer-BioNTech vaccines reported side effects than people who received a booster of the same brand.

"What may be happening is that the road map your body had for the first one is a little different with a changed vaccine," said Charlotte Baker, a professor of epidemiology at Virginia Tech. "The new vaccine has to teach it a few more things, so you may get new side effects. The vaccines all are trying to do the same thing, but each has their own way of doing it. And teaching your body new things—that's good."

On the other hand, some people may not experience any side effects after receiving a booster shot—but experts say that this doesn't mean the shot isn't working. If you get side effects, "at least you know [the booster] is working," Baker said. "But if you don't, I wouldn't say it's not working. Your body response might not do anything outwardly."

Overall, many experts highlight the importance of getting a booster shot to protect against coronavirus infection, especially in the face of the spreading omicron variant.

"Getting the booster has been proven to significantly reduce your risk of contracting SARS-CoV-2 compared to only getting a primary vaccine series," said Abraar Karan, an infectious disease physician at Stanford University. "Because of omicron especially, we would urge that people get boosted, avoid crowded areas and try to wear high-grade masks if they have to be in a crowded public area." (Kaur/Logan, Los Angeles Times, 12/15; Owens, Axios, 12/16; Eldred, ”Goats and Soda," NPR, 12/10)