No, the vaccine will not give you COVID-19

Some participants in COVID-19 vaccine trials have experienced fevers and swelling as side effects of the immunization. Todd Brown, a registered pharmacist and professor at Northeastern, explains that these side effects are normal and prove that the vaccine is doing its job. Photo by Ruby Wallau/Northeastern University

There are a lot of myths floating around about the COVID-19 vaccine, but Todd Brown, a registered pharmacist and clinical instructor in the department of pharmacy and health systems sciences at Northeastern, can disprove at least one of them: The vaccine, he says, will not give you COVID-19. 

The two COVID-19 vaccines that are expected to be approved for emergency use authorization later this month do not use any part of the SARS-CoV-2 virus to create immunity, making it impossible for the vaccine alone to give someone COVID-19, Brown explains.   

Both of these vaccines, which are being produced by pharmaceutical companies Pfizer and Moderna, are mRNA vaccines. They create immunity by enabling cells to produce proteins that mimic parts of the SARS-CoV-2 molecule, triggering the immune response without introducing the virus. 

In fact, it would be impossible for most vaccines to give you the diseases they are intended to prevent, Brown explains.

Todd Brown, a registered pharmacist and clinical instructor in the department of pharmacy and health systems sciences at Northeastern, explains the side effects of the COVID-19 vaccine. Photo by Ruby Wallau/Northeastern University

Most vaccines create immunity when either an inactive version of the pathogen or isolated components of a pathogen are introduced to the body. In either case, enough of the pathogen is present to stimulate an immune response, but not enough to cause disease. 

“A lot of people think the flu shot gives them the flu, but if the virus is inactive, like it is in a flu shot, it can’t give you the infection,” Brown says.

People often confuse the side effects of a vaccine—which can mimic those of an infection—with an actual infection. But those side effects are really just our immune systems revving up, Brown says.   

Like many other vaccines, the COVID-19 vaccine can cause side effects, such as fever and swelling at the injection site. Brown says these are normal reactions to any vaccine and not indicative of an infection. 

“People might be relieved to know that those side effects are actually signs for how we know the vaccine is working,” he says.

Vaccines are supposed to activate the immune system and teach it which foreign pathogens to attack. “They give our bodies roadmaps for fighting disease,” Brown says. Swelling and fevers are part of that natural immune response. 

For example, some COVID-19 vaccine trial participants have experienced egg-like welts on their arms after receiving an injection. That’s because some of the vaccine lingers at the injection site, which is usually in the upper arm, Brown explains. “There’s a little war going on between the vaccine and the body. That process increases the flow of blood to that area, and that causes the swelling.” 

Some participants in the COVID-19 trials also experienced fevers in response to the vaccine, another natural mechanism used to fight bacteria and viruses. An increased body temperature helps immune cells travel to the site of infection faster. Getting a low-grade fever after receiving a vaccine means your immune system is activated and ready to fight an infection if needed, Brown explains.  

Adverse side effects such as these are common with vaccines that are highly effective—Pfizer’s and Moderna’s vaccines prevent COVID-19 in more than 90% of people. 

The same phenomenon occurs in other highly effective vaccines, such as the shingles vaccine. It’s common for people to get a sore arm, a low-grade fever, and generally feel unwell after receiving this shot, Brown explains. 

There is a possibility that people who get the COVID-19 vaccine still develop the disease, according to the Centers for Disease Control and Prevention. It usually takes a few weeks for the body to build immunity to a vaccination, so it’s possible to become infected with the coronavirus right before or right after receiving the COVID-19 vaccine. But this coincidence, Brown says, should not be misinterpreted as causation. 

In most cases, he says, if people experience side effects from the vaccine, they should know that not only are these not symptoms of COVID-19, but they’re actually signs that the vaccine is doing its job. 

For media inquiries, please contact Marirose Sartoretto at or 617-373-5718.