Key takeaways:
The updated fall 2025-2026 COVID-19 vaccine booster won’t make you test positive for COVID-19.
Expected side effects of the vaccine include fever, chills, muscle pain, headaches, fatigue, and arm pain. These don’t mean you have COVID.
You still may get a COVID infection and test positive. But the updated vaccine will decrease the chances of severe illness, hospitalization, and death.
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There’s a new COVID-19 vaccine for fall 2025-2026. But it’s not a booster. This year’s COVID vaccine has been reformulated, so it’s not simply a repeat of last year’s shot. The 2025-2026 COVID vaccine is based on the monovalent JN.1 lineage (specifically the LP.8.1 strain) to match currently circulating viruses. 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? The short answer is: no. COVID tests detect the virus itself, not the immune response triggered by vaccination. So, if you test positive after getting the shot, it means you were exposed to the virus — and not that the vaccine itself caused it. Here’s why.
COVID vaccines 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.
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 2025-2026 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 2025-2026 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.
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 by now, 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
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 aren’t symptoms of the COVID vaccine. They may be signs of COVID infection. If you develop those symptoms, talk with a healthcare professional.
How long does immunity last with the new fall COVID vaccine?
This is an important question now that we’re in the 2025‑26 season and have a newly updated shot. The short answer is: Protection against infection can decline over time, but protection against severe illness, hospitalization, and death stays strong.
The 2025-2026 data isn’t available yet. But, in general, studies show that after vaccination, the immune system produces a strong response that helps prevent serious disease for months. Protection against mild or asymptomatic infection may drop somewhat over several months, especially if new variants are circulating. But, even then, vaccines still reduce the chance of getting very sick.
The newest fall vaccine targets the variants currently spreading in communities, which helps keep immunity relevant. How long protection lasts depends on factors such as:
How well the vaccine matches circulating variants
Your immune system
Whether you’ve had prior COVID infection
More research is ongoing, but the key takeaway is clear: The updated vaccine helps you stay protected from severe COVID outcomes, even if breakthrough infections are still possible.
Can you get COVID after being vaccinated in 2025?
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.
Frequently asked questions
On a rapid antigen test, a positive result usually shows two lines:
One next to the “C” (control)
One next to the “T” (test)
The lines don’t have to be perfect: Even a faint second line counts as positive. PCR tests don’t show visible lines. Instead, they report a “detected” or “positive” result from a lab.
Most people test positive for about 5 to 10 days after their symptoms start. Rapid tests tend to turn negative sooner than PCR tests, which can stay positive for weeks even after you’re no longer contagious. That’s because PCR tests detect tiny pieces of viral RNA that can linger after the infection clears.
No, COVID vaccines don’t cause long COVID. Long COVID happens after an infection with the actual virus, not after vaccination. In fact, studies show that being vaccinated lowers your risk of developing long COVID if you do get infected later.
On a rapid antigen test, a positive result usually shows two lines:
One next to the “C” (control)
One next to the “T” (test)
The lines don’t have to be perfect: Even a faint second line counts as positive. PCR tests don’t show visible lines. Instead, they report a “detected” or “positive” result from a lab.
Most people test positive for about 5 to 10 days after their symptoms start. Rapid tests tend to turn negative sooner than PCR tests, which can stay positive for weeks even after you’re no longer contagious. That’s because PCR tests detect tiny pieces of viral RNA that can linger after the infection clears.
No, COVID vaccines don’t cause long COVID. Long COVID happens after an infection with the actual virus, not after vaccination. In fact, studies show that being vaccinated lowers your risk of developing long COVID if you do get infected later.
The bottom line
Getting the updated COVID vaccine won’t cause you to test positive on PCR or rapid antigen tests. After getting any of the shots, you might have symptoms like body aches, swollen lymph nodes, and headache. These are common side effects of the vaccines that can last a couple of days. If your symptoms last longer, or you’ve been exposed to someone with COVID infection, it’s a good idea to get tested.
Why trust our experts?
References
Centers for Disease Control and Prevention. (2025). Getting your COVID-19 vaccine.
European Centre for Disease Prevention and Control. (2025). Does COVID-19 vaccination reduce the risk and duration of post COVID-19 condition?
Link-Gelles, R., et al. (2022). Effectiveness of 2, 3, and 4 COVID-19 mRNA vaccine doses among immunocompetent adults during periods when SARS-CoV-2 Omicron BA.1 and BA.2/BA.2.12.1 sublineages predominated — VISION Network, 10 states, December 2021–June 2022. Morbidity and Mortality Weekly Report.
Novavax. (2025). Novavax's Nuvaxovid 2025-2026 formula COVID-19 vaccine approved in the U.S.
U.S. Food & Drug Administration. (2024). Antibody (serology) testing for COVID-19: Information for patients and consumers.
U.S. Food & Drug Administration. (2025). COVID-19 vaccines (2025-2026 Formula) for use in the United States beginning in fall 2025.
