Will You Test Positive for COVID-19 After Getting the Updated Fall COVID Vaccine ‘Booster’?

There’s a new COVID-19 vaccine for fall 2024-2025. But it’s not a booster. That’s because this new vaccine doesn’t have anything to do with previous versions that targeted the original COVID virus. 

Instead, the 2024-2025 COVID vaccine targets the new KP.2 and JN.1 variants. Just like the flu shot is different every year, the new COVID shot is different from the previous generation of COVID shots.  

The rollout of this updated COVID vaccine comes with many questions. Among them, will the COVID vaccine cause a positive COVID test? People are getting the updated vaccine at a time when cases of COVID are rising. So, if you have a positive COVID test after you get the updated vaccine, did the vaccine cause the positive test? The short answer is “no.” The COVID vaccine doesn’t cause a positive COVID test. Here’s why.

Why getting the updated COVID vaccine won’t cause you to test positive for COVID 

COVID vaccines don’t contain the virus that causes COVID, so they can’t cause an active infection. Because of that, a COVID vaccine won’t make you test positive for COVID infection. The rapid tests used to detect the virus that causes COVID don’t test for immunity. They detect active COVID infection, by testing for viral particles. 

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Because of the way the COVID vaccines work, they don’t use any live virus. Instead, the mRNA vaccines (Pfizer and Moderna) tell the body’s cells to make a specific protein (a harmless piece called the “spike protein”), so that the body can build antibodies against it. To put it simply, the vaccine teaches your body how to fight the virus without you having to be infected with the virus that causes COVID. The updated fall 2024-2025 Pfizer and Moderna vaccines use this same process.  

The Novavax vaccine takes a more conventional approach to creating immunity than the mRNA vaccines. It contains a protein from the virus that stimulates the body to make antibodies against it. The updated fall 2024-2025 Novavax vaccine also protects against new variants of the COVID virus. And just like the mRNA vaccines, there’s no way of getting COVID from the Novavax vaccine.

Can you test positive on a COVID antibody test if you’ve been vaccinated?

The vaccine can make you test positive on some antibody tests. That’s the point — to develop antibodies to the virus that causes COVID. A COVID antibody test is different from a rapid test. It tests for whether you have immunity to the virus that causes COVID — not whether you currently have a COVID infection.

If you have a positive COVID antibody test, you have some degree of protection against the virus that causes COVID. This is for one of two reasons: 

• You’ve had a past COVID infection.

• You’ve been vaccinated against COVID.

But it’s not always that simple. Some people who get COVID illness or the vaccine may not develop antibodies afterward, so they may not test positive for antibodies. 

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At this time, experts don’t recommend getting a COVID antibody test after the vaccine to “see if it worked.” That’s because the commercially available antibody tests don’t always check for the same antibodies associated with the vaccine. Also, a positive antibody test doesn’t guarantee a certain level of immunity.

COVID antibody tests were common early on in the pandemic, but they’ve fallen out of favor more recently. This is because these tests only tell you if you’ve been infected by COVID or vaccinated against it at some point in your life. And since so many people have either had a COVID infection or have been vaccinated against it at this point, these tests are no longer as helpful.

Will you have symptoms of COVID infection after getting vaccinated?

After vaccination, you may develop symptoms, such as:

• Fever

• Chills

• Fatigue

• Headache

• Body aches

• Swollen lymph nodes

• Arm pain

These are common signs that your body is creating an immune response and preparing protection against the virus that causes COVID. Of course, some of those are similar to symptoms of COVID infection. But they’re less severe. 

It’s always possible to get a COVID infection before your body has fully mounted its immune response to the vaccine. This is especially true if you were exposed shortly before getting the vaccine or before becoming fully vaccinated. 

So how do you tell the difference between side effects and illness? Vaccine side effects typically go away after 24 to 72 hours. So, if they’re not easing up, talk with a healthcare professional. Importantly, loss of taste and smell and sore throat are not symptoms of the COVID vaccine and may be signs of COVID infection. If you develop those symptoms, talk with your primary care provider. 

How long does immunity last with the new fall COVID vaccine?

This has become an important question as public health officials try to understand vaccine and booster schedules. Unfortunately, the answer is not straightforward. 

A review of studies found that vaccine immunity against COVID dropped 20% to 30% at 6 months. But vaccines remained protective against severe disease. In fact, the vaccine proved to be 56% effective at preventing severe disease as long as 1 to 2 years after getting the shot.

Here’s one thing to keep in mind: Those studies were before the Omicron wave, and COVID variants have changed a lot since then. The updated COVID vaccines target the variants that are currently spreading in our communities. Currently, those are the JN.1 and KP.2 variants.

Researchers can’t be sure how long protection against COVID from the newest wave of vaccines might last. How long vaccine immunity lasts depends on how well the vaccines are matched to the variants that are currently spreading through the community, as well as how good those variants are at evading the new vaccines.

More time and data will help scientists understand more about how long the newer COVID vaccines provide protection. So far, though, it’s clear that vaccines protect people against severe illness, hospitalization, and death.

Can you get COVID after being vaccinated in 2024?

Yes, it’s possible to get COVID after being vaccinated. COVID vaccines help prevent you from getting COVID after you’ve been exposed to it, but they’re not perfect. After getting vaccinated, some people might avoid getting COVID altogether. Other people who have been vaccinated, might still get COVID. 

What’s important to know, though, is that if you get COVID after being vaccinated, you won’t get as sick from it as you would have if you didn’t get the vaccine. What this means is that your symptoms might be less noticeable, or you might have lower chances of hospitalization or death from COVID.

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Written by:

Sonya K. Narla, DO

Sonya K. Narla, DO, is a board-certified family medicine physician, educator, bioethicist, and writer. She practices primary care for all age groups in Phoenix, AZ.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Farzon A. Nahvi, MD

Dr. Nahvi is an emergency medicine physician and author of “Code Gray: Death, Life, and Uncertainty in the ER.” He works clinically at Concord Hospital in Concord, New Hampshire, and is a clinical assistant professor of emergency medicine at the Geisel School of Medicine at Dartmouth. Prior to this, he worked as an ER physician and clinical assistant professor of emergency medicine at the Mount Sinai Health System, NYU Langone Health, NYC Health + Hospitals/Bellevue, and the Manhattan VA. He is a graduate of Cornell University and NYU School of Medicine.

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