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Last updated January 28, 2021. 6 minute read

How does the COVID-19 vaccine work?

The COVID-19 vaccine works by training your immune system to recognize a specific part of the virus, so when you come into contact with it in the real world, your immune system is primed and ready to fight back.

Dr Chimene Richa Md Written by Chimene Richa, MD
Reviewed by Mike Bohl, MD, MPH

Measles, tetanus, and flu shots—all of the vaccines you’ve heard about work essentially the same way. 

Vaccines safely expose your immune system to a germ in a way that doesn’t cause a full-blown infection. For instance, some vaccines will use a small piece of the virus they’re working against, while others use inactive or weakened versions of the virus. 

The ultimate goal is to let your immune system see the virus, mount an immune response against it, and create long-lasting antibodies. Your immune system then stores these antibodies like memories for future use. So if you are ever exposed to the real virus, your body already has the tools it needs to fight it off—no time wasted! Your immune system launches into battle, ramping up an army of antibodies to attack the virus. Let’s take a closer look at how this whole process actually works. 


  • The COVID-19 vaccine works by training your immune system to recognize a specific part of the virus, so when you come into contact with it in the real world, your immune system is primed and ready to fight back.
  • The coronavirus has an outer crown (corona means crown in Latin) of spike proteins that it uses to enter your cells.
  • COVID-19 vaccines provide your body’s protein-making factories with the blueprints to build the viral spike proteins so you can make antibodies against them.
  • You cannot get COVID-19 from the vaccine because it doesn’t contain the active virus. If you’re experiencing side effects that’s a sign your immune system is working against those spike proteins.

How does the COVID-19 vaccine work?

Coronavirus disease 2019 (COVID-19) vaccines work by exposing your immune system to some part of the virus in a safe way. This is done by targeting a specific part of the virus particle, which we noted earlier is called a spike protein. These crown-like spike proteins are what enable the virus to enter your system. 

The virus that causes COVID-19, called the SARS-CoV-2 virus, has an outer crown (or “corona”) of protein spikes. 

These protein spikes are one of the first things that your body detects when it encounters the virus. After your body recognizes them as foreign proteins, it triggers an immune response. This process can take a while, which gives the virus time to reproduce and spread throughout your body.

You might be wondering why you can’t get sick if you’re exposed to the virus’s spike proteins. Because the vaccine exposes your cells to just the proteins and not the rest of the virus, it can’t make you sick. So how does the vaccine accomplish this? In a very clever way, actually.

The COVID-19 vaccine contains the genetic material that codes for those spike proteins. Just like an architect needs the blueprints to build a house, the virus particles need genetic material to create spike proteins. 

Rather than trying to cram the proteins themselves into the vaccine, scientists used blueprints of genetic material instead so the architects in your cells can recreate the spike proteins. The viral genetic material (mRNA or DNA, depending on the brand of vaccine) doesn’t stick around and degrades quickly, so you don’t have viral blueprints floating around forever. Because only the protein spike code is in the vaccine, the virus can’t build itself in your cells (CDC, 2020).

What happens after the COVID-19 vaccine enters my body?

After you get the vaccine, your cells start to produce viral spike proteins. The immune system sees these proteins and recognizes them as foreign proteins that should not be there. It then mounts an immune response and creates antibodies against the spike proteins. This way if you ever come in contact with the real virus, your immune system is ready to attack.

All of the COVID-19 vaccines currently available require two doses to effectively rev up your immune system. Since the vaccines activate an immune response, it’s common to experience side effects like soreness at the injection site, headaches, and fatigue. These symptoms do not mean you have full-blown COVID-19, rather are a sign your immune system is working hard against those spike proteins. Since the second dose can give you more of a response than the first one, some people notice more side effects after the second vaccine. 

After you receive both doses, it can take 1–2 weeks (depending on which vaccine you get) until you’re fully protected against COVID-19. The vaccines are also very effective, with the Moderna vaccine 94.5% effective and the Pfizer/BioNTech version 95% effective (FDA, 2020a; FDA, 2020b).

Scientists still don’t know whether you can carry COVID-19 and give it to someone else (without getting sick yourself) after getting the vaccine. Even after you have been vaccinated, you should continue with all COVID-19 protocols, such as wearing a face mask, practicing social distancing, avoiding large gatherings, and washing your hands frequently. 

Debunking myths about how the COVID-19 vaccine works

Myth: The COVID-19 vaccine changes your DNA

Vaccines, like those developed by Pfizer-BioNTech and Moderna, use what’s called mRNA to pass along the spike protein blueprints. Your DNA is stored in the nucleus of your cells where mRNA cannot enter. Therefore, it does not interact or change your DNA in any way. The only purpose of using the viral genetic material is to trigger your body into making the viral spike proteins. After this, the virus protein mRNA is broken down naturally by your cells naturally (CDC, 2021). Your immune system then makes antibodies to fight the spike proteins and protect you against future COVID-19 infections.

Myth: The vaccine makes you sick with COVID-19

None of the COVID-19 vaccines in use today contain live COVID-19 viruses, so they cannot make you sick. They only provide the information that your cells need to create viral spike proteins, encouraging your immune system to produce antibodies. You need the entire virus particle reproducing itself throughout your body to get sick with COVID-19. 

You may experience side effects of the injection, like injection site soreness, headaches, and fatigue. These are signs that your immune system is working against those spike proteins and not an indication of COVID-19 illness. It takes weeks for your body to develop full protection against COVID-19. Therefore, it is possible to get sick with COVID-19 shortly after getting the vaccine if you were exposed to the virus before your body has had time to build up immunity.

Myth: The COVID-19 vaccine implants a microchip tracker

This is most definitely false. A misquoted internet discussion with Bill Gates on Reddit, a popular internet forum, started these rumors. Gates mentioned that having “digital certificates” for health records may be an option in the future—but there was no mention of “microchip implants.” In a statement given by the Bill and Melinda Gates Foundation to Reuters, “The reference to ‘digital certificates’ relates to efforts to create an open-source digital platform with the goal of expanding access to safe, home-based testing” (BMGF, n.d.; Reuters, 2020).

Myth: The COVID-19 vaccine is made from previously unknown and untested technology

Researchers have been studying mRNA vaccines since the 1990s. Clinical trials of mRNA vaccines and DNA vaccines for HIV, rabies, Zika virus, and influenza have been in the works for years—so it is not as if scientists created this technology specifically for the COVID-19 virus (Pardi, 2018; Montgomery, 1997). In response to the global pandemic, governments provided money, and social media helped recruit volunteers, allowing researchers to compress the vaccine development timeline. The vaccine data was then reviewed by the U.S. Food and Drug Administration (FDA), which determined that the vaccines were safe and effective enough to grant Emergency Use Authorizations (EUAs) so that the vaccines could be distributed nationwide (FDA, 2021c).