Published on December 14, 2020

Explaining the Science of the Covid Vaccines

How do mRNA (Covid) vaccines work, and how are they different from the seasonal flu vaccine?

Doctor in white jacket looking at camera
Christopher Petrey, D.O. is an infectious disease doctor locate at Ephraim McDowell Specialty Center, 216 West Walnut Street in Danville, Kentucky.

The flu vaccine we receive annually is an inactivated vaccine made from multiple strains of dead influenza virus particles.  When your body recognizes the dead virus particles, which have antigens sticking to them, it automatically notices that something foreign is inside your body and it responds by making antibodies.  The antigens and antibodies fit together like a lock and key.  The antibodies your body creates stay with you for several months.  If you catch the flu virus, the antibodies immediately recognize the antigens and attach to them, inactivating the virus particles and either protecting you from getting the flu or lessening the symptoms and duration of illness.  When you receive the flu vaccine, it is typical that you may experience injection site pain, mild achiness and fatigue for 24 to 36 hours.  These symptoms occur as your body is making the antibodies.  It is not possible to get the flu from the flu vaccine.  Anyone who gets the flu would have already been exposed to the virus and was in the process of getting sick before getting the vaccine.

The Covid vaccines are mRNA (messenger RNA) vaccines and follow a different process to create the antibodies to fight the virus.  Once injected with the Covid vaccine, the mRNA particle “codes” or “creates” spike proteins that are specific to the surface of the SARS CoV 2 virus particles.  Your body will then recognize the spike protein as foreign and will attack it and form antibodies specific to it.  If you are exposed to Covid and it gets in your system, the high level of antibodies will immediately attack the spike protein on the Covid virus and inactivate it, thus protecting you from getting the infection or lessening the symptoms and duration of illness.  After getting the mRNA vaccine, your body will create a robust response as it makes the antibodies.  You can expect to experience injection site pain, body aches, fever and headaches for the first 24 to 48 hours.

Should I be concerned that the vaccine is a new technology and was rushed for approval too soon?

The vaccine was definitely rushed, due to the fact that nearly 300,000 people have already died from SARS CoV 2.  Rushing a vaccine is not uncommon when the entire world is pouring millions of dollars into research and development.

The science behind mRNA vaccines is NOT new and has actually been around for several years.  Previously, mRNA vaccine technology has been used in research for cancer treatments.  Each type of cancer, similar to a virus, has specific proteins (antigens) covering the outside.  The mRNA for the targeted protein is injected and the body makes the antibodies and then attacks the antigens on the cancer cells.  The future looks favorable for more mRNA vaccines to be developed.

Should I be concerned about long-term side effects?

No.  Most vaccine reactions occur within the first couple of months, and are very rare to begin with.  These vaccines have been given to patients participating in the trials since June and July, which would be ample time to notice serious side effects if they were going to occur.

How do clinical trials for drugs and vaccines work?

There are three phases to every clinical trial before any drug or vaccine is approved:

Phase 1:  The agent is first tested in a human subject to make sure it is safe.  A variety of different doses are typically given, to ensure the safety at each dose level.

Phase 2:  The “best dose” that was determined to be safe in Phase 1 is then given to a group of patients (usually between 100 and 300 people).  During this phase, researchers begin to understand the safety and effectiveness of the drug/vaccine being tested, and their studies focus on adjusting treatment doses.  Researchers are also monitoring common side effects and whether patients improve as a result of the drug/vaccine.  During Phase 2 trials, neither the researcher nor the patient knows whether the patient receives the actual drug/vaccine or a placebo.

Phase 3:  This is the largest phase of the trial with the most number of people enrolled.  During this phase, participants come from all walks of life with various pre-existing conditions selected.  Again, neither the researcher nor the patient knows whether the patient receives the actual drug/vaccine or a placebo.  Typically, if the drug works, you see people in the group who received the drug get better while people in the group who received the placebo tends to not get better and may actually catch the disease trying to be prevented.  This proves the effectiveness of the drug/vaccine.  Both Pfizer and Moderna have data from their Phase 3 trials showing that 95% of the people who got the vaccine did not get sick.  For the Moderna vaccine, the remaining 5% did not develop severe disease from Covid.

Christopher Petrey, D.O. is an infectious disease doctor located at Ephraim McDowell Specialty Center, 216 West Walnut Street in Danville, Kentucky. For more information call (859) 239-5860.