Sonya Narla, DOSonya Narla, DO, is a board-certified family medicine physician, educator, bioethicist, and writer who practices primary care for all age groups.
Key takeaways:
- The COVID-19 vaccine won’t make you test positive for COVID, though you may test positive for antibodies.
- Fever, chills, muscle pain, headaches, fatigue, and arm pain are expected side effects of the vaccine and do not mean you have COVID-19.
- It’s unclear how long vaccine-induced immunity lasts, but current studies suggest at least 3 months (and up to 6 months with the Pfizer vaccine).
It’s hard to believe a full year has passed since the COVID-19 pandemic changed the world. And at long last there seems to be some hope in sight with three different vaccines and increasing availability of the vaccines.
One common concern among patients is if getting the COVID-19 vaccine could make you test positive for the virus, which could prevent you from traveling, returning to work, attending social functions, and more. A related point of confusion is the difference between COVID-19 symptoms and COVID-19 vaccine side effects. Read on for answers.
The short answer is no.
The two types of tests used to detect active COVID-19 infection are the polymerase chain reaction (PCR) test and the rapid antigen test. These are both viral tests, meaning they test for active infection to see if you currently have COVID-19. The COVID-19 vaccines do not actually contain the COVID-19 virus and cannot cause active infection — so you won’t test positive for COVID-19 from the vaccine.
The mRNA vaccines (Pfizer and Moderna) instruct our cells to produce a specific protein (a harmless piece called the “spike protein”), against which our bodies begin to build antibodies. To put it simply, the vaccine teaches your body how to fight the virus without you having to be infected with COVID-19.
The Johnson & Johnson vaccine works similarly. But instead of using mRNA to instruct the cell to create the spike protein, the J&J vaccine uses an inactivated adenovirus (so not a coronavirus) to deliver instructions to cells on how to fight COVID-19. The inactivated virus cannot infect you since it is not “alive” and is simply being used to deliver information.
It’s also worth pointing out that neither the mRNA vaccines nor viral vector vaccines alter your DNA.
Can you test positive on a COVID-19 antibody test if you’ve been vaccinated?
It is possible that the vaccine could cause you to test positive on some antibody tests. That’s the point of the vaccine: to develop antibodies to COVID-19.
Generally, a COVID-19 antibody test is used to detect past COVID-19 infection. A positive COVID antibody test suggests that you may have had a past infection (or exposure to the virus protein through a vaccine) and may have some degree of protection.
But it’s not always that simple: Some people who get COVID-19 may not develop antibodies afterwards and may not test positive for antibodies.
At this time, experts do not recommend getting a COVID antibody test after your vaccine to “see if it worked” because the commercially available antibody tests do not always check for the same antibodies associated with the vaccine.
Will I display symptoms of coronavirus after getting vaccinated?
After vaccination, you may develop certain symptoms like fever, chills, fatigue, headache, body aches, swollen lymph nodes, and arm pain. These are common signs of your body starting to mount its immune response and prepare protection against COVID-19. Of course, some of those symptoms are similar to symptoms of COVID-19, but less severe.
It’s always possible that you could contract COVID-19 infection before your body has fully mounted its immune response, especially if you were exposed shortly before receiving the vaccine or prior to 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 are not improving be sure to speak with your provider. Importantly, loss of taste and smell are not symptoms of the COVID-19 vaccine and may be signs of COVID-19 infection. If you develop those symptoms, speak with your provider.
Has anyone gotten COVID-19 after being fully vaccinated?
Yes, but it is relatively rare. COVID-19 vaccines are not 100% effective at preventing COVID-19, so it makes sense that people have gotten COVID-19 even after being fully vaccinated. It’s a good reminder that fully vaccinated people are not invincible and still need to take many of the same precautions as before.
That said, studies show the vaccines are very good at preventing severe cases of COVID and hospitalizations. So while you can still get COVID-19, you’re less likely to become very sick with it after vaccination.
How long does immunity last after vaccination?
This is the big question. Unfortunately, we don’t know that exact information yet. According to the Centers for Disease Control and Prevention (CDC), experts are still working to determine how long immunity lasts after vaccination. This takes time and careful, controlled monitoring. The new variants also add another unknown piece to the puzzle and are being studied now as well.
Even though we don’t have answers just yet, the clinical trials indicate that vaccine-induced immunity should last 3 months minimum. Recently, Pfizer released an official update confirming their vaccine had high efficacy (91.3%) for up to 6 months following the second vaccine and no serious safety concerns in clinical trial participants.
The New England Journal of Medicine also recently published a study that suggests the Moderna vaccine has efficacy for up to 6 months, similar to the Pfizer vaccine. However, Moderna has yet to issue an official update.
As time goes on and the trial participants in all vaccine trials are monitored for a longer period, we expect the efficacy time frames for the vaccines to increase.
The bottom line
You cannot contract COVID-19 from any of the current COVID-19 vaccines and will not test positive on a viral test.
It is possible to have some short-term side effects from the vaccines like fever, chills, muscle pain, arm pain, fatigue, and headaches that may seem similar to COVID-19. Those side effects are simply a sign of your immune system gearing up to produce antibodies and typically only last 24 to 72 hours.
If you have symptoms that last longer, or experience loss of taste or smell, shortness of breath, cough, or other symptoms, it is important to discuss these further with your provider. It is still possible to contract COVID-19 prior to or around receiving your vaccine.
Read more:
- Getting the COVID-19 Vaccine? Here’s What to Expect
- Why Are COVID-19 Side Effects Worse After the Second Shot?
- Did the COVID-19 Vaccine Work if I Didn’t Feel Any Side Effects?
- Mexican Workers on Border Get Vaccines to Aid Them.
- When Will It Get Too Hot for the Body to Survive?
Talk to the vaccine skeptic in your life about these myths.