Booster shots are the best protection against omicron


Booster shots are the best protection against omicron. Photo by Cyrus McCrimmon, for UCHealth.

Katie Kerwin McCrimmon, UCHealth

Booster shots are the best protection against omicron and people who receive boosters are nearly 50 times less likely to be hospitalized if they get COVID-19, according to the newest research.

So, who is eligible for booster shots now? Where can you get them? Do mix-and-match boosters work better than sticking with the same type of COVID-19 vaccine than you initially received? For the latest guidance from the CDC on booster shots, click here.

As the omicron variant continues to spread around the world and public health experts predict that omicron’s impact soon will be felt throughout the U.S., we consulted with UCHealth vaccine expert, Dr. Thomas Campbell, to answer your newest questions about COVID-19 booster shots.

Campbell ran clinical trials for COVID-19 vaccines at UCHealth University of Colorado Hospital on the Anschutz Medical Campus. He is also a professor of medicine and infectious diseases at the University of Colorado School of Medicine.

Campbell’s key message is this: if you are eligible, get your booster shot now.

Who should get COVID-19 booster shots. An older woman gets her vaccine at UCHealth Universtiy of Colorado Hospital in Aurora.
Health experts in the U.S. now are encouraging everyone ages 16 and older who is eligible for a booster shot to get it as soon as possible. Photo by Cyrus McCrimmon for UCHealth.

“Booster shots are the best tool that we have to fight omicron right now,” Campbell said.

While health experts like Campbell still are awaiting detailed research about how well vaccines match up against omicron, it’s already clear that booster shots should significantly bolster immunities.

Who is eligible for booster shots and how can you get them?

As of December 9, health experts with the U.S. Centers for Disease Control and Prevention (CDC) now are encouraging everyone ages 16 and older who qualifies for a booster dose to get one as soon as possible. Learn more about the CDC’s specific recommendations. Learn about how to get free vaccines and booster doses at UCHealth vaccine clinics. On Jan. 5, 2022, the CDC recommended that anyone age 12 and older who received the Pfizer vaccine is eligible for a booster shot five months after receiving the second dose of Pfizer.

What is the research that shows that people who have boosters are almost 50 times less likely to be hospitalized than unvaccinated individuals?

Those data come from Colorado public health officials and are based on analyses of COVID-19 infections and hospitalizations in Colorado between September and November.

“It’s becoming clearer and clearer how important booster doses are,” said Scott Bookman, Colorado’s COVID-19 incident commander.

To underscore the critical role of boosters, Bookman shared the following data.

People who have received booster doses are:

  • 47.5 times less likely to be hospitalized with COVID-19 than people who haven’t been vaccinated at all.
  • 7 times less likely to become infected with COVID-19 than those have not received any vaccinations.
  • 4 times less likely to become infected with COVID-19 than people who have received two doses of the Pfizer or Moderna vaccines or one dose of the Johnson & Johnson vaccine.

State officials are joining Campbell and national health experts in calling for people to immediately get boosted.

“The case is clear. There is no doubt how important these booster shots are,” Bookman said.

Learn more about that research.

Why should younger people get booster doses?

dr. Thomas Campbell
Dr. Thomas Campbell.

“The main reason for young people to get booster doses is to protect themselves. They will also protect their parents, grandparents and other people their age who might be more susceptible to severe cases of COVID-19 based on their medical conditions,” Campbell said.

“By getting young people boosted, we will help thwart the spread of the delta and omicron variants. Younger people are less likely to get hospitalized or die from COVID-19, but some do. So that’s an important reason for 16 and 17-year-olds to get boosters.”

Campbell wants people to know that hospitals remain full of critically ill patients of all ages, most of whom are unvaccinated.

He recently cared for a critically ill person in his early 20s.

“He’s been on a ventilator for weeks. He’s not immunocompromised. He has no medical conditions aside from obesity, which describes 30% of our population. He’s in a critical state. Some young people get gravely sick from COVID-19,” Campbell said. “It doesn’t happen as often (with younger people) but there’s still a risk.”

“By getting boosted, you will protect yourself and help thwart the spread of the delta and omicron variants,” Campbell said.

What do researchers know so far about how well booster shots will help people fight omicron?

The overall gist of new research is this. Vaccine effectiveness with the standard two doses is lower against omicron than it has been with delta and previous strains. But boosters are helping bolster people’s ability to fight omicron. Early reports from South Africa, where omicron was first detected, show that vaccinated people or those who previously recovered from COVID-19 may get milder illnesses if they get infected with the omicron variant.

A study from South Africa, where the omicron variant was first detected, showed that a booster dose increased vaccine protection against symptomatic infection of COVID-19 from about 35% to 75%.

Campbell said it’s an excellent sign that people who have received booster shots are faring better when they are contracting omicron.

In preliminary studies, Pfizer scientists also found that booster doses increase the body’s ability to fight omicron.

“The Pfizer researchers say antibody levels after the third dose will be high enough to protect against omicron,” Campbell said.

“Delta hit Israel before the U.S. and they started boosting their population before we did,” Campbell said. “The Pfizer vaccine (the primary vaccine used in Israel) works very well to prevent hospitalization. This study compares people who received two vaccine doses with individuals who received three (or a booster shot).”

Campbell’s takeaway from the study: “Everyone who is eligible should get a booster.”

Moderna also announced that a third dose of its vaccine was highly protective against omicron.

Moderna’s scientists found that their 50-microgram booster — which is half the regular Moderna — increased a person’s antibodies by roughly 37-fold. A full dose of 100 micrograms was even more powerful, raising antibody levels about 83-fold compared with pre-boost levels, Moderna leaders said on a conference call.

Another new study from the University of Oxford in the United Kingdom that has not yet been peer-reviewed found that antibody levels fell dramatically when patients who had received only two vaccine doses had omicron introduced to their blood samples.

But the researchers expected that people who received booster doses would fare much better.

“Real-world effectiveness data has shown us that vaccines continue to protect against severe disease with previous variants of concern,” said Oxford University professor, Teresa Lambe, who is one of the study authors. “The best way to protect us going forward in this pandemic is by getting vaccines in arms.”

How does a booster shot help increase immunities?

“Omicron has more mutations in the spike protein (the part of the SARS-CoV2 virus that attacks people) than delta does,” Campbell said.

“That lower protection can be overcome by getting higher levels of antibodies. That’s why we boost,” he said.

Boosters work by reawakening the body’s army of infection-fighting T and B cells so they are poised to attack new viruses.

What is your prediction for what omicron will do? How much time do I have to get my vaccines or booster shots?

Get your first vaccine doses if you haven’t gotten them already or your booster shot if you are eligible as soon as possible.

The most recent data from the Centers for Disease Control and Prevention (CDC) show that omicron is already responsible for 2% of all new COVID-19 cases nationwide and 13% of new cases in New York and New Jersey. As expected, omicron is spreading fast.

Ideally, Campbell is encouraging people to get booster shots before omicron overwhelms the U.S.

Campbell and health experts with the CDC are predicting that omicron could be widespread in the U.S. within weeks. It’s now spreading throughout Europe and in areas of the northeast U.S.

“What happens in Europe will be very predictive of what will happen in the U.S. If in the next two weeks, we see omicron become predominant in Europe, then by mid-January, it likely also will be predominant in the U.S.,” Campbell said.

“We are fortunate in a way that Europe is between us and other parts of the world. It helps us prepare for what is coming,” Campbell said.

As variants like omicron and delta continue to develop, will we have to get fourth doses of COVID-19 vaccines?

At the moment, Campbell said there is no data to suggest that fourth doses will be necessary. But time will tell.

“We don’t know. We’re still too close in time to the point when everyone has gotten boosters. We just started giving booster doses in the U.S. in late September and early October.  It took six months for antibody levels to decline. If they decline again, it won’t happen sooner than six months from now,” Campbell said.

Do mix-and-match or “heterologous” vaccines work?

Yes. Especially for people who received the Johnson & Johnson (J&J) vaccine, it’s very wise to switch to either Pfizer or Moderna for a second dose, Campbell said.

“If you had a J&J vaccine, you will get 10 times higher antibodies with a Moderna booster and a little less than that with a Pfizer vaccine,” Campbell said.

For those who received Pfizer or Moderna, the choice is less clear (and not worth worrying too much about). Just get the booster dose that you can get most easily and quickly.

“If you had Moderna, you get the highest antibody level by getting a Moderna booster,” Campbell said. “If you had Pfizer, you get the highest antibody levels by getting a Moderna booster, but the difference (between getting a Pfizer booster) is very small and might not be clinically meaningful.”

Learn more about mix-and-match boosters. Read a recent study about mix-and-match boosters.

Everyone age 5 and up should get vaccinated and those older than 16 who are eligible should get boosted for protection from omicron variant

As omicron infections continue to increase around the world, health experts in the U.S. are recommending COVID-19 vaccines for everyone ages 5 and older and booster doses for people ages 16 and older who had their initial vaccines.

Research shows that COVID-19 vaccines are remarkably effective in preventing hospitalizations and deaths, but the effectiveness of vaccines wanes over time. Booster doses two months after a J & J vaccine or six months or longer after two initial doses of Pfizer or Moderna vaccines can jumpstart vaccine efficacy.

Mike and Nannette Wien pose after getting their COVID-19 booster shots at UCHealth University of Colorado Hospital
Mike and Nannette Wien pose after getting their booster shots at UCHealth University of Colorado Hospital. Mike recently won the Boston Marathon in his age group. He’s eager to encourage everyone to stay healthy and get vaccinated. Photo by Cyrus McCrimmon for UCHealth.

Health experts agree that the best way to end the pandemic as soon as possible is for all eligible unvaccinated people to get their first doses of vaccines as soon as possible. (Learn more about getting COVID-19 vaccines and booster doses.)

Booster shots will help bump up immunities for those who had their vaccines several months ago.

“We know booster shots play an important role in the fight against COVID-19, and we’re still in the midst of a pandemic,” said Dr. Michelle Barron, senior medical director of infection prevention at UCHealth. “Vaccine efficacy may diminish over time with the potential risk for increased susceptibility to breakthrough infections.”

COVID-19 infections and hospitalizations in Colorado remain very high, prompting Barron and others health experts to urge people to get initial vaccines immediately and booster doses as soon as people if they are eligible. Coloradans should continue to be very cautious and wear masks in crowded indoor spaces.

Here are answers to many basic questions about booster shots.

What is a booster shot?

A booster shot is an additional dose of a vaccine after a person has received an earlier dose (or two in the case of COVID-19 mRNA vaccines). An extra dose “boosts” your immune system, sparking better protection against an illness.

How can I get a booster vaccine?

UCHealth patients can log in the online health portal, My Health Connection and can schedule booster doses online. Learn more about COVID-19 vaccines.

Why do we need boosters?

It’s normal for some vaccines to wane or become slightly less effective over time. Research both by the COVID-19 vaccine makers and independent scientists is showing that the mRNA COVID-19 vaccines made by Pfizer and Moderna are waning several months after recipients get their first doses. Also, the delta variant is extremely contagious and it has caused hundreds of thousands of new infections. The omicron variant is also expected to cause more infections in the new year.

What is the specific CDC advice about who should get a booster shot?

The newest guidance from CDC health experts encourages anyone age 16 and older who had their first two doses of Pfizer or Moderna or a single dose of the Johnson & Johnson vaccine at least two months ago to get a booster dose.

Joan Hooker, 89, received her vaccine on Sunday at her church, Shorter Community AME in Denver. Who should get booster shots now?
Older adults were the first to get COVID-19 vaccines a year ago and also the first to get booster doses. Now, everyone who is 16 and over and eligible for a booster should get one. Here, Joan Hooker, 90, received her first COVID-19 vaccine dose early in 2021 at her church, Shorter Community AME in Denver. Photo by Cyrus McCrimmon for UCHealth.

When should I get a booster?

If you received a J & J vaccine, you should get a booster shot two months or longer after your vaccine. If you received Pfizer or Moderna vaccines, you should get a third dose at least five months after you received Pfizer and six months after you received Moderna for the second time.

Is the booster dose for Moderna different than the initial Moderna dose?

Yes. Research shows that half a dose of Moderna works well as a booster dose. So, the Moderna booster doses will now be 50 micrograms compared with 100-microgram initial doses.

Have the Pfizer and J & J booster dose amounts changed?

No. People who receive Pfizer or J & J will continue receive the same doses that they previously did.

What’s the difference between a booster dose and a third shot for immunocompromised people?

A third shot is now the standard initial dose for immunocompromised people. These are people who have specific conditions that make it hard for them to build up antibodies to fight infections.

Immunocompromised people should get a third shot about one month after their first two doses of mRNA vaccines like Pfizer and Moderna.

Booster shots, on the other hand, are for everyone else.

Do I have to have a doctor’s order to get a booster shot?

No. Just make an appointment to get a booster dose if you are eligible. No doctor’s order is required. And both vaccines and booster doses are free. Learn more about vaccine locations in Colorado.

How much do booster doses cost?

Booster doses are free, just like the initial COVID-19 vaccine doses.

Can I get a flu shot at the same time I get my booster shot?

woman feeling sick and drinking tea - flu cases could be bad in 2021 and 2022
If you haven’t gotten your flu shot yet, do so right away. Both flu and various strains of the virus that causes COVID-19 are circulating now. Photo: Getty Images.

It’s safe to get flu and COVID-19 vaccines or booster shots at the same time. But, some vaccine clinics only offer COVID-19 vaccines. You may need to schedule a flu shot separately. Please check with your doctor.

If you haven’t gotten your flu shot yet, you should do soon as soon as possible. Flu is here and the omicron variant may cause a new wave of COVID-19 infections, causing a possible “twindemic.” 

Is it true that the Moderna vaccine is staying effective longer than the Pfizer vaccine?

Yes. Research like this study in the New England Journal of Medicine has shown that both the Pfizer and Moderna vaccines are highly effective and very safe. It’s also common for some vaccines to diminish in their effectiveness over time. The Pfizer vaccine seems to be waning (or becoming somewhat less effective) more quickly than the Moderna vaccine.

According to data from the CDC, vaccine effectiveness in preventing hospitalizations for COVID-19 was highest for people who received Moderna vaccines — 93% — compared with efficacy rates of 88% for people who had received Pfizer vaccines and 71% for those who had received the Johnson & Johnson vaccine.

What should people who received the single-dose Johnson & Johnson vaccine do?

About 15 million people in the U.S. received J & J vaccines, far fewer those who have received Moderna and Pfizer vaccines. J & J recipients should get a second vaccine dose two or more months after they got their J & J vaccine. People who received J & J will get better protection if they opt for a Moderna or Pfizer booster dose.

What if I am vaccinated and got a breakthrough case of COVID-19? How long should I wait to get a booster dose?

You should wait until you have recovered from COVID-19, no longer have symptoms including a fever and no longer are in isolation: about 10 days for most people and about 20 days if you are immunocompromised.

In general, people should get their booster doses as soon as they are healthy and qualify for the booster, says Barron, the UCHealth infectious disease specialist.

“It is thought that people potentially should wait up to 90 days after their infection to get a shot. But, no one has studied the ideal time frame,” Barron said. “We recommended that if you have fully recovered from COVID-19, you feel well and are no longer in isolation, you should get your COVID-19 booster shot whenever it’s convenient for you.”

I had a breakthrough case of COVID-19 and needed monoclonal antibodies? How long should I wait to get my booster shot after having received monoclonal antibodies?

People who have received monoclonal antibodies should wait 90 days before getting their booster dose.

Are there enough vaccines available in the U.S. for people to get both their initial doses of vaccines and their booster doses?

Yes. CDC health experts say that vaccines are plentiful. So, supply is not a problem. Get your initial vaccines immediately if you have not already. And, if you are 16 or older and eligible for a booster dose, get it as soon as possible.

Who is considered immunocompromised?

  • Cancer patients.
  • Organ and stem cell transplant patients.
  • People with immunodeficiencies.
  • People living with HIV.
  • Patients who are being treated with immunosuppressive medications such as chemotherapy, TNF blockers to stop inflammation tied to rheumatoid arthritis, certain biologic agents like rituximab and high-dose corticosteroids.

Are boosters recommended because of breakthrough cases, COVID-19 infections in fully-vaccinated people?

  • Increases in the number of breakthrough cases of COVID-19 have caused health experts to recommend booster shots for some people.
  • But, most people getting sick with COVID-19 now are unvaccinated. And, an overwhelming majority of hospitalized COVID-19 patients have not been vaccinated.
  • Some immunocompromised people have been getting COVID-19 even if they are fully vaccinated. That’s because their bodies are unable to create the same number of antibodies as healthy people, and thus, they cannot mount the same defense against COVID-19.
  • In particular, people with cancer, rheumatoid arthritis, lupus and patients who have had organ or bone marrow transplants and those who are taking immunosuppressive medications have not been able to build up the same level of antibodies to COVID-19 as people without underlying health conditions.

How long are coronavirus vaccines effective?

Both the Moderna and the Pfizer vaccines — which account for more than 95% of U.S. vaccinations so far — remain highly effective for at least six months after people receive their second dose. The efficacy data is based on studies of how clinical trial participants have fared over time. The efficacy has declined slightly over the summer and fall, both because of the delta variant and the waning effect.

What are the side effects of the third dose?

So far side effects for boosters are similar to those that people experienced when they got their first two doses.

Individuals may experience a sore arm, headache, muscle aches, a low-grade fever or feel tired. These side effects typically last fewer than three days. Experts from Pfizer told FDA and CDC officials during recent testimony that many people receiving booster doses have experienced fewer side effects after third doses than they did with their second dose.

Who should skip booster doses?

Young, fully-vaccinated, healthy people probably don’t need booster doses because the vaccines are working very well to protect them from severe infections, hospitalizations and death from COVID-19, according to CDC experts.

Because the vaccines are holding up so well for young, healthy people, some infectious disease experts were hesitant to recommend booster doses for all adults.

In addition, in very rare cases, young men who have been vaccinated have experienced heart issues known as myocarditis. Due to this very rare vaccine side effect, some younger men, ages 18 to 30, may decide to skip booster doses.

Are people in other countries getting booster doses?

Yes. Israel has led the way. In Israel, older adults began getting booster doses in the early summer and now, anyone who is 12 or older can get a booster dose. Other countries like the United Kingdom and Germany also are offering booster doses.

Is there a test to determine how strong your immunity is against COVID-19?

Yes, there are antibody tests. But, doctors do not recommend antibody testing outside of clinical trials. The best way to stay healthy is to get your primary COVID-19 vaccines as soon as possible, then to get a booster dose if you qualify or fall into one of the recommended groups.

If I had COVID-19 already, do I still need vaccines?

Yes. Studies like this one are finding that vaccines are even more protective than natural antibodies. And, people can get COVID-19 after having previously had it. So, it’s best to get fully vaccinated.

Are antibodies from vaccines or previous infections the only mechanisms in our body that are fighting COVID-19 infections?

No. Researchers are finding that antibodies from vaccines team up with natural “memory” cells in our bodies. These are known as “B” and “T” cells.  CDC researchers estimate that antibodies play a majority role in fighting COVID-19 infections, but “B” and “T” cells are also crucial.

I have Multiple Sclerosis (MS). I need to get infusions every six months. My medication is called Rituxan. Do I need to wait for a couple of months after getting my infusion to get my booster shot?

No. COVID-19 infections can be dangerous for people with conditions like MS.

“While Rituxan can decrease the efficacy of the vaccine, with rates of COVID-19 still high, most clinicians recommend not waiting to get the booster shot if you are eligible,” Barron said. “The protection may not be as good as if you wait, but then you are left unprotected for the time frame until you can get it and you are at risk of infection. So the short answer is: If you qualify for a booster, you should just get it regardless of when the Rituxan dose was given.”