Do You Need a Covid-19 Booster Shot? Here’s What to Know

Updated: Aug. 30, 2021

Covid-19 booster shots are coming. How are they the same—and different—from the first vaccinations?

When can you get a Covid booster shot?

In August, the White House announced that Covid-19 booster shots should start the week of September 20. Healthy people should be eligible for booster shots on a rolling basis, starting eight months after their first vaccines.

While the move still needs approval from the Food and Drug Administration (FDA) and a go-ahead from the Centers for Disease Control and Prevention Advisory Committee on Immunization Practices, many expect boosters to be available on President Biden’s timeline.

Why is this happening, and why now? Here’s everything you need to know, according to doctors.

Boosters aren’t the same as third doses

It’s worth explaining the difference between a booster shot and the third vaccine dose that the FDA recently approved for immunocompromised people.

That third dose, explains William Schaffner, MD, former board member of the Infectious Diseases Society of America, “is for people whose immune systems did not respond optimally to the two [original] doses.”

It’s well recognized that transplant patients and other immunocompromised individuals don’t mount as robust a response to the primary vaccine when compared to healthy people, explains Dial Hewlett, MD, medical director of the division of disease control at the Westchester County Department of Health in White Plains, New York.

That puts them at higher risk of having a breakthrough Covid-19 infection.

This third dose is not a booster. An immunocompromised person starting their vaccine series today would get the third dose at least 28 days after the second dose of Pfizer or Moderna.

By contrast, a booster is an additional dose for healthy people. Think of it as “continuing education” for the immune system.

“It wakes the immune system up again and boosts it to another level,” says John Zaia, MD, director of the Center for Gene Therapy at City of Hope in Duarte, California.

If your head is spinning, you’re not alone. “It’s easy to get confused because we’re talking about the same dose of vaccines, but there’s an important difference in timing and who it’s used for,” says Vincent Hsu, executive director of infection control at AdventHealth.

Boosters are for healthy people

Although healthy people typically mount a strong immune response to the initial vaccine or vaccines, it’s normal for that antibody response from a vaccine to slowly diminish over time, says Dr. Schaffner, a professor of infectious diseases at Vanderbilt University in Nashville.

This is true of other vaccines as well. Consider the boosters recommended for tetanus and chickenpox, among others.

Covid-19 and Covid-19 vaccines are so new that scientists are still trying to determine exactly how long immunity from the vaccine lasts.

H. Dirk Sostman, MD, president of the Houston Methodist Academic Institute, says there’s data showing for either natural infection or post-vaccination that your antibody levels go down and reach kind of a low steady state in about six to eight months.

Health officials had discussed the possibility of a Covid-19 booster months ago, but were collecting more data before making a recommendation.

Repeated covid vaccine vials on blue backgroundYulia Reznikov/Getty Images

The original vaccine still works

It’s normal for the effect of vaccines to decline over time. And because the vaccines were so effective at the beginning, they’re still working.

As immunity wanes, vaccinated people do have a higher chance of breakthrough infections, but these are still relatively rare. Vaccinated people who get sick are much less likely to end up in the hospital or die from Covid-19.

Most of the people who are now getting very sick with Covid-19 have not been vaccinated.

The Delta variant plays a part

All three vaccines available in the U.S. are less effective against Delta than against the original variant, but they’re still effective. That’s just another reason boosters may be a good idea.

“We are seeing some data from Israel suggesting that getting a booster, which is not yet authorized, may further protect the population against the Delta variant,” says Dr. Hsu.

“There’s no doubt that the Delta variant has thrown a wrench into this. If not for Delta, we may not have required boosters so soon.”

More variants are on the horizon, including Lambda, which was first identified in Peru and has now traveled to the U.K., says Dr. Schaffner.

The same people will get priority

All the boosters will be given to individuals eight months after the original series. The same people prioritized for the shots the first go-around will also be first in line for boosters.

“If the booster is approved, sometime toward the end of September, the first people who became eligible for the vaccine—nursing home residents and healthcare providers—would get the booster,” says Dr. Schaffner.

Some people are already getting boosters “off label.” You need a doctor’s prescription to do this.

(Here’s what you need to know about how to get the Covid-19 vaccine.)

Boosters should be available at the same places

After the chaotic roll-out of the Covid-19 vaccines, systems and protocols are now in place to deliver boosters more smoothly. Details haven’t been worked out, but you’ll likely be able to get them at the same places: pharmacies, immunization centers, and doctors’ offices.

“I think people feel it’s so easy to get a vaccine now, boosters won’t be a problem, but we’ll have to wait and see,” says Dr. Zaia.

One thing we do know: Take your vaccination card so it can be updated.

The side effects will be similar

“So far what we’ve heard from the CDC is that those people [who] have gotten their third dose of a vaccination, and could include a booster off label, the side effects are similar to those experienced with the first 2 doses,” says Dr. Hsu. “The most common effects we see are fatigue, headaches, fever.”

Most people will also have a sore arm. There’s still a chance of allergic reactions or other more serious side effects, but these are rare.

Some experts speculate that certain people may have more severe reactions just because their immune systems are already primed to react, adds Dr. Hsu.

(Read how 8 people experienced their Covid-19 vaccines.)

Boosters probably won’t be “mix and match”

“Right now, the FDA and CDC recommend that you get the same product that you received for the first and second doses,” says Dr. Hsu.

It’s not clear yet if the Pfizer and Moderna shots are interchangeable. It’s even less clear with the Johnson & Johnson vaccine. (This week, Johnson & Johnson released preliminary data showing that a second dose of its shot significantly increased antibody production.)

A trial underway in the U.K. suggests that mixing the vaccines may actually produce a stronger immune response.

Boosters may be given with the annual flu shot

This could happen and it could happen as early as September, says Gregg Sylvester, chief medical officer of Seqirus, the second largest influenza vaccine manufacturer in the world.

The CDC now says that Covid-19 vaccination at the same time as another vaccination is possible, including on the same day.

“This idea of giving a Covid vaccine in one arm and influenza in the other is absolutely appropriate [in approved populations],” says Dr. Sylvester. No one knows how severe this year’s flu season will be, but it makes sense to act to prevent a twindemic.

A study (not yet peer-reviewed) that looked at giving the influenza vaccine simultaneously as the Novavax Covid-19 vaccine (not available in the U.S.) found similar side effects and no differences in effectiveness. Other studies are ongoing.

There’s also interest in seeing if you can combine the two vaccines into one formulation, says Dr. Hewlett.

(Here’s how to know if your symptoms are Covid-19 or the flu.)

The first vaccines are still important

If you are unvaccinated, it’s definitely not too late to start the series, and there’s plenty of supply.

“Getting the primary vaccine is critically important against severe disease and even mild infections,” says Dr. Hsu. “We do know that breakthrough infections do occur, but the frequency still is relatively low, especially when compared with infections in unvaccinated people.”