COVID-19 mRNA Vaccines: How do they work?

There has been a lot of confusion about the two most available COVID-19 mRNA vaccines that are manufactured by Pfizer and Moderna.  Here are answers to some of the most frequent questions I’ve gotten in clinic:

  1. How do vaccines work?

Vaccines work by stimulating your immune system to recognize disease-causing organisms like viruses.  By recognizing and killing the organisms early, your immune system can help you avoid getting sick or can decrease the severity of symptoms and illness if you do get sick.

Vaccines were pioneered by Edward Jenner, a British physician, in 1796.  Dr. Jenner  used cowpox virus, a weak variant of the smallpox virus, to immunize people against the smallpox virus.  People who were injected with the cowpox vaccine were immune to smallpox.

Modern vaccines such as the flu vaccine are similar to Jenner’s cowpox immunization.  Attenuated viruses (viruses that are altered so they cannot infect you) or inactivated viruses (killed viruses) are injected to teach your immune system to identify and attack viruses before they can make you sick.

  1. What is mRNA?

To understand mRNA, we must first understand DNA.  Put simply, DNA is our genetic code.  It is a long complicated set of genes that code for everything in our bodies including proteins that our cells may need.  When our cells need a protein, they read a section of DNA and produce a small message to give to our cellular machinery.  That message is read by the cellular machinery and the protein is produced.  The message created by reading DNA is called messenger RNA or mRNA.  mRNA does not change, alter or affect the DNA at all.

Using mRNA for prevention and treatment of disease is not new; in fact, it has been researched over the past thirty years in the field of cancer treatment.  The primary difficulty with mRNA is that it is very fragile; this is why the current mRNA vaccines in use have to be frozen.  Once thawed, the vaccine must be used rapidly before the mRNA in the vaccine breaks down or degrades.  Prior to now, this fragility has limited mRNA’s use in immunizations and cancer treatment.   Only in the past two years have scientists have been able to stabilize the mRNA enough to make it clinically useful.

When COVID-19 hit, pharmaceutical companies that have been researching mRNA for cancer treatment switched their research to developing mRNA vaccines for COVID-19.  That is why the vaccines were able to be so quickly developed, studied and approved for emergency use.  Full authorization for the vaccines was given by the FDA in August of 2021.

  1. How does the mRNA vaccine work?

The mRNA vaccine contains a small snippet of mRNA that codes for the COVID-19 “spike protein”.  The spike protein is the protein on the surface of the COVID-19 virus that allows the virus to attach to and infect your cells.  On its own, separate from the rest of the COVID-19 virus particle, the “spike protein” is not infectious.  When the mRNA is injected into your arm, your cellular machinery reads the mRNA and produces the protein that it encodes.  Your body then produces an immune reaction to the spike protein and learns to block the virus from infecting your cells.

It is important to understand that mRNA vaccines are focused- they have our bodies produce just one protein for our immune system to learn and defend against.  Other types of vaccines, like the flu vaccine or varicella (chickenpox) contain multiple components for our immune system to mount a defense against.  The current mRNA vaccines produce just one protein for our immune system to learn and attack.  The likelihood of unusual reactions is lower with such a tailored type of vaccine.

  1. How effective are mRNA vaccines?

The Pfizer and Moderna mRNA vaccines showed an effectiveness of approximately 95%.  That means that the mRNA vaccines prevented 95% of people from becoming infected with COVID-19.  The success rate is spectacular.  These vaccines also show high protection against the Delta variant of COVID.

In the Moderna trial 30,000 people were enrolled and in the Pfizer trial 43,000 people were enrolled.  For perspective, these clinical trials were very large.

  1. What symptoms do people develop from the vaccines?

Most people have mild reactions of arm soreness, fatigue, muscles aches, and occasionally low grade fever. This can last up to 48-72 hours.

  1. What are the risks of the vaccine?

There were very few significant adverse reactions to the vaccines.  In the Pfizer trial  four people developed a neurological condition called Bell’s palsy, a limited partial facial weakness that usually resolves spontaneously over several months.  Severe allergic reactions have been extremely rare, approximately three to five episodes per million doses.

Short and long term effects of the vaccine are being rigorously tracked, monitored and studied by the CDC and other organizations.  Over 22 million (and counting!) vaccinated people in the U.S. are voluntarily participating in an easy-to-use smartphone based vaccine monitoring program called V-SAFE through the CDC.  You can participate as well- information will be given to you at your vaccination appointment.  You can find more information about V-SAFE here:

  1. After I have my two COVID-19 vaccine shots, do I still have to take precautions?

Yes!  The vaccine immunity does not happen immediately.  Studies showed that it took approximately 2 weeks after the first Pfizer and Modena vaccine for antibody effectiveness to reach 50%.  After the second shot, it took an additional 2 weeks after to reach 95% efficacy.

We know that it is possible to have COVID-19 without symptoms, but still be able to spread the virus to others.  The vaccine cannot prevent all cases of COVID- about 10% of all vaccinated people may get COVID.  It is also possible for immunized people to have asymptomatic COVID-19 infection and be able to spread it to others, but if an immunized person does get COVID, the risk of death or ICU admission is greatly reduced.  It is very important to continue to follow all COVID-19 precautions, including continuing to wear a mask in public, maintaining 6 ft. distance from others, and washing your hands frequently even if you have been vaccinated.

  1. Do I need a booster shot?

Current recommendations for vaccinated individuals who are immunocompromised or on immune modulating medications is to receive a booster shot at least 28 days after their second Moderna or Pfizer vaccine.  See for more details on how immunosuppression may affect vaccine response.

Overall, the mRNA vaccines show excellent effectiveness against COVID-19 with few known adverse reactions.  In contrast, COVID-19 itself can cause severe illness and death, especially in the 65+ population and in people between the ages of 35-65.   The Delta variant of COVID is more infectious than the initial “alpha” COVID virus and more virus is made in the body with Delta.  We are also just beginning to understand “Long-COVID”, where patients who have had COVID-19 infection, including mild disease, continue to have longer-lasting symptoms and medical issues including heart, lung and neurologic symptoms. Getting vaccinated against COVID-19 greatly decreases the possibility of these types of outcomes. I encourage you to highly consider this information when deciding whether to get the COVID-19 vaccine.

For more vaccine information go to or for Buncombe County.

If you would like information on integrative approaches for COVID-19 prevention or how integrative medicine can help with Long-COVID symptoms, please contact the office at 828-333-3339.