Since they were introduced, COVID-19 vaccines have been the best way to protect yourself and others from the coronavirus. But there are a lot of questions about the doses that come after the initial vaccines, such as: What’s the difference between a booster shot and an immunocompromised dose? What’s a bivalent booster shot? Who should get a booster shot and when?

We answer all these questions and more below.

Booster shot vs. immunocompromised dose: Is there a difference?

Yes. There’s a difference between COVID-19 vaccine booster shots and immunocompromised doses. Though they both provide extra protection against COVID-19, they’re used for different reasons which we’ll get into in the following sections.

What is a COVID-19 booster shot?

The COVID-19 booster shot is used to increase the initial vaccine's level of effectiveness and extend the length of protection.

Receiving the initial COVID-19 vaccine series and the recommended boosters are the best way to protect yourself and others from getting sick. Even if you’ve had COVID-19 after being fully vaccinated, you should still get a booster after you’ve recovered. There’s also a chance that getting boosted can reduce your chance of getting long-COVID.

How are COVID-19 booster shots different from other vaccine doses?

The first COVID-19 booster shots that became available in the fall of 2021 are the same as the original vaccine – sometimes at smaller doses. These booster shots were monovalent and are only made with one strain of the coronavirus – the original Wuhan strain.

The Moderna and Pfizer booster shots approved in the fall of 2022 include additional components to offer more protection against newer strains of the coronavirus. These newer booster shots are “bivalent” boosters, which means they’re made with components from both the original Wuhan strain of the coronavirus and the Omicron strain. Specifically, the new bivalent boosters include components of BA.4 and BA.5, the subvariants of Omicron that account for the most COVID-19 cases.

The Novavax booster approved in the fall of 2022 is another dose of the original monovalent Novavax vaccine–it doesn't include components from newer subvariants. Despite this, it's being offered to people who are unable or uninterested in getting a booster of a mRNA vaccine.

Bivalent booster shots vs. monovalent booster shots

We know that the monovalent boosters continue to provide great protection against COVID-19. Data from the Centers for Disease Control and Prevention (CDC) shows that COVID-19 vaccines and booster shots greatly reduce the severity of symptoms if you get a breakthrough case of COVID-19.

In fact, during the Omicron spike, getting a monovalent booster dose significantly increased protection against COVID-19 – people who had got a booster shot were 23 times less likely to be hospitalized than people who weren’t vaccinated.

Since the bivalent boosters contain components of the Omicron subvariants, scientists believe that the new boosters will further reduce the number of people who get COVID-19 – and the number of people who have severe symptoms.

Does the need for additional booster shots mean that the COVID-19 vaccine isn't effective?

No. COVID-19 booster shots don’t mean there’s anything wrong with the COVID-19 vaccine. Rather, this is what normally happens with many vaccines – your immune response can decrease over time.

That’s why there are booster shots for illnesses such as chickenpox, tetanus, mumps and measles, to name a few – and why you should get a flu shot every year.

How long is the COVID-19 booster shot effective?

The CDC continues to look into how long booster shots protect against COVID-19. Research showed the original monovalent booster shots provided good protection for at least four months – even against the Omicron subvariants. At this point, scientists don’t yet know how long the protection from the bivalent boosters will last.

Who’s eligible for a COVID-19 vaccine booster shot?

Most fully vaccinated people over the age of 6 months old are eligible to receive a COVID-19 booster shot.

Who isn’t eligible for a booster at this time?

• People who aren’t fully vaccinated (you’re fully vaccinated against COVID-19 about two weeks after the final dose from your initial series)
• Children 6 months old to 4 years old who got the Pfizer vaccine after December 2022 – these children have already received the Pfizer bivalent vaccine as a third dose in their initial vaccination series
• Babies who are younger than 6 months old

When to get a COVID-19 booster shot based on your initial vaccine

You may wonder which booster to get and when. For the best protection, get a booster as soon as you're eligible. While an mRNA bivalent booster is the preferred option, there are times when the Novavax monovalent vaccine may be an option.

When to get an mRNA bivalent booster dose

Eligible people can get a bivalent booster once it’s been at least two months since their previous dose. People who currently have COVID-19 should wait until all their symptoms go away before getting a bivalent booster.

When to get a Novavax booster

People age 18+ can get a booster dose of the Novavax monovalent vaccine six months after completing their initial series. You may consider the Novavax booster if other booster vaccines are unavailable or if you have reactions to a component of an mRNA vaccine. You should not get the Novavax booster if you've already had a booster shot of another vaccine.

What is a COVID-19 immunocompromised dose?

For most people, receiving the prescribed doses of the COVID-19 vaccine (two for Moderna, Pfizer and Novavax; one for Johnson & Johnson) causes enough of an initial immune system response to protect them from falling ill with COVID-19.

But for people with weakened immune systems, the initial vaccine may not produce enough protective antibodies to prevent them from getting the disease. In these cases, people may need an additional dose of a COVID-19 vaccine for full protection.

Who is eligible for a COVID-19 vaccine immunocompromised dose?

People 5 years old and older who are moderately to severely immunocompromised may be eligible to receive an additional dose. Usually, an immunocompromised dose is given 28 days after your second dose, but your doctor may suggest different timing based on what they think you need.

You may be considered immunocompromised if you:

• Had an organ transplant
• Had stem cell transplants within the past two years
• Have severe primary immunodeficiency
• Are being treated for active cancer
• Have advanced or untreated HIV
• Are being treated with drugs that may suppress your immune system, such as high-dose corticosteroids

Which immunocompromised dose can I get?

The choice of immunocompromised dose depends on your age and the vaccine used in the initial vaccine.

The following is the typical timing of additional doses and booster shots for people who are immunocompromised. But your doctor may suggest different timing or additional doses, based on what they think is best for you.

Even after you get an immunocompromised dose, it’s still recommended you continue to take other steps to avoid getting COVID-19, including wearing a mask and avoiding large crowds.

If you’re eligible for a third dose and received your initial vaccines through HealthPartners, you likely have already received an email or text message from us and can schedule your next dose online. But you don’t have to be a HealthPartners patient to schedule your immunocompromised dose.

If you’re not sure if you’re eligible, call your clinic.

Are COVID-19 vaccine booster shots and immunocompromised doses safe?

COVID-19 vaccines are incredibly safe – they’ve protected millions of people against COVID-19, usually with few side effects. Immunocompromised doses and monovalent booster shots are made from the COVID-19 vaccine, making them equally safe. And as we mentioned, the new bivalent boosters build on the safety of the original vaccine and include additional components to make them more effective against Omicron.

What are the possible side effects of a COVID-19 vaccine booster shot or immunocompromised dose?

Do you remember the side effects that you had with your initial vaccine dose(s)? Chances are that your side effects will be very similar this time around.

For most people, the common side effects are usually fatigue and feeling pain around where they got the shot. Less commonly, people experience headache, muscle pain, chills, fever and nausea. These side effects usually only last a couple days.

Moving forward as things change

It may seem like things with COVID-19 keep changing, and it’s true. Boosters and additional doses demonstrate that we’re learning more about COVID-19 so we can control the spread of the coronavirus and keep communities healthy.

We know that the vaccines work. According to the CDC, unvaccinated people are more likely to get COVID-19 than vaccinated people. There’s also a huge difference in the severity of symptoms between vaccinated and unvaccinated people. If someone who is vaccinated gets breakthrough COVID-19, they usually have mild COVID-19 symptoms that can be treated at home.

Getting vaccinated is still the best thing you can do to prevent COVID-19. And, getting the appropriate boosters or immunocompromised dose can help extend your protection against the coronavirus.