Understanding COVID-19 Vaccines

Understanding COVID-19 Vaccines 1200 1200 nodMD

Understanding COVID-19 Vaccines

The vaccine landscape for coronavirus disease 2019 (COVID-19), caused by the SARS-CoV-2 virus, has quickly evolved since the virus emerged in late 2019. While preventing cases of COVID-19 is an important step in combating this pandemic, preventing severe illness that results in intubation, prolonged disability, or even death are especially important.1 Thankfully, the first vaccines for COVID-19 have been recently authorized for use in the United States. On December 11, 2020, the United States Food and Drug Administration (FDA) issued its first emergency use authorization (EUA) for the Pfizer/BioNTech vaccine, BNT162b2 for the prevention of COVID-19. On December 18, 2020, the FDA issued its second EUA for the Moderna, mRNA-1273 vaccine for the prevention of COVID-19 as well.2 These innovative vaccines are the first-ever messenger RNA (mRNA) vaccines developed for humans.

What are mRNA vaccines?

Researchers have studied mRNA vaccines on many viruses such as influenza, Zika, rabies, and cytomegalovirus (CMV).3 The revolutionary speed that mRNA vaccines can be developed offers a significant advantage and potential turning point in combating this pandemic. The ability to inject mRNA into animals dates back to 1990.1 Traditional vaccines involve an injection of antigens such as purified proteins or polysaccharides, inactivated viruses, or attenuated (weakened) viruses.1 The mRNA vaccines contain genetic material (mRNA) to help create a spike protein that the SARS-CoV-2 virus attaches to in order to infect human cells.1 The vaccine is packaged with lipid nanoparticles to protect the mRNA from being degraded by the body when injected. When the vaccine is injected into a muscle, such as the deltoid muscle, the lipid nanoparticles containing the mRNA inside are taken into the cells of the muscle where ribosomes detect and decode the mRNA resulting in the production of the spike protein. Furthermore, the mRNA does not enter the nucleus, which contains the DNA of a cell and cannot be reproduced or integrated into the DNA.1 The production of the spike protein elicits an immune response where the presenting cells detect, ingest, and take the protein to regional lymph nodes where T cells and B cells produce antibodies.1 In the future, technology may allow for one vaccine to provide protection against multiple diseases.3 Cancer research has used mRNA to elicit an immune response to help target specific cancer cells as well.3

The Pfizer/BioNTech COVID-19 vaccine

The Pfizer/BioNTech vaccine is given in two doses, 21 days apart and authorized in individuals 16 years of age and older. About 43,538 participants underwent randomization with 21,720 receiving the Pfizer/BioNTech vaccine and 21,728 receiving placebo.1 Among the participants who had no evidence of existing or prior COVID-19 infection, there were eight cases of COVID-19 among those who received the Pfizer/BioNTech vaccine and 162 cases among those in the placebo group.1 Among 37,706 participants, the median age was 52 years. Furthermore, 83% were White, 9% were Black or African-American, and 28% were Hispanic or Latinx.2 Also, 35% were obese and 21% had at least one co-existing condition.2 The incidence of serious adverse events was similar in the vaccine and placebo groups, 0.6% and 0.5 % respectively.2 Among 21,621 people who received the Pfizer/BioNTech, only four related serious adverse events were reported: shoulder injury related to vaccine administration, lymphadenopathy (swollen lymph nodes in the armpit), ventricular arrhythmia, and right leg paresthesias (numbness, tingling, or prickling sensation).2 There were no deaths considered by the investigators related to either the vaccine or placebo.2

The Moderna COVID-19 vaccine

The mRNA vaccine is also given in two doses, 28 days apart but is authorized in individuals 18 years of age and older. The United States National Institute of Allergy and Infectious Diseases, and Biomedical Advanced Research and Development Authority sponsored the clinical trial, which was part of Operation Warp Speed.2 There were more than 30,000 participants enrolled. Of these, 25,645 received their second vaccination.2 The trial enrolled those over the age of 65 (7,000 participants), people with chronic illnesses (5,000 participants), and minorities (11,000 participants).2 The most common adverse reactions were pain at the injection site, fatigue, headache, joint pain, muscle pain, and chills. Severe adverse reactions occurred in 0.2% to 9.7% of participants, which were more frequent after the second dose and were less frequent in participants 65 years of age or older.4 Furthermore, lymphadenopathy was a solicited adverse reaction observed after any dose in 21.4% of vaccine recipients less than 65 years of age and in 12.4% of vaccine recipients 65 years of age or older compared to placebo recipients, which occurred in 7.5% in those less than 65 years of age and in 5.8% in those 65 years of age or older.4 A total of 30 severe COVID-19 cases were reported, which were all in the placebo group.4 Throughout the safety follow-up period to date, there were three reports of Bell’s palsy (facial paralysis) in the vaccine group but one in the placebo group.4


Both vaccines have reported around 95% efficacy, which is highly unexpected considering many vaccines for respiratory illnesses achieve around 60% to 80% efficacy.1 However, duration of immunity and the need for revaccination are still unknown at this time.1


Pfizer/BioNTech expects to be able to produce around 50 million vaccine doses in 2020 and 1.3 billion doses in 2021.1 Moderna expects to produce 20 million doses by the end of 2020, and 500 million to 1 billion doses in 2021.1 However, storage requirements can be a significant factor in the distribution of these vaccines. The Pfizer/BioNTech’s vaccine has to be stored and transported at -80 ° C requiring specialized freezers or dry ice containers that many sites are not equipped with.1 Furthermore, once the vaccine is thawed, it can only remain in the refrigerator for 24 hours. The Moderna vaccine is easier to store and can be placed in a standard freezer at – 20° C for up to 6 months or at room temperature for up to 12 hours.1


People with a history of severe allergic reaction (anaphylaxis) to any ingredient in the mRNA vaccines should not get vaccinated at this time. People with a history of anaphylaxis to other vaccines or injectable therapies may still be able to receive the mRNA vaccines but should talk with their healthcare provider first.5 However, the following groups of people are not contraindicated in getting the mRNA vaccines: family history of anaphylaxis, non-serious allergy to other vaccines or injectable therapy, allergy to any oral medication, and those with a history of food, pet, insect, venom, environmental, latex, or other allergies not related to injectable therapies.2


As of this writing, there is no data on the safety of mRNA vaccines in pregnant women. In December 2020, the American College of Obstetricians and Gynecologists (ACOG) recommended that the vaccines should not be withheld from pregnant individuals who meet criteria for vaccination. Furthermore, the Society of Maternal Fetal Medicine (SMFM) stated that the safety risk of mRNA vaccination for pregnant or lactating women appears to be low.2 However, a discussion with a health care provider can help make a more informed decision.

What about the new strain identified in the United Kingdom?

A new variant strain of SARS-CoV-2 has been recently discovered in the United Kingdom (UK), which has been predicted to be possibly more transmissible than other circulating strains of SARS-CoV-2. Currently, scientists are trying to learn more about this variant strain, especially to better understand whether currently authorized vaccines will still be effective.6 At this time, there is no evidence that this variant causes more severe illness or an increased risk of death.6


  1. Pichichero ME. Understanding Messenger RNA and Other SARS-CoV-2 Vaccines. Medscape. Published December 15, 2020. Accessed December 22, 2020. https://www.medscape.com/viewarticle/942654
  2. Vaccines in Development. Infectious Diseases Society of America. Updated December 13, 2020. Accessed December 22, 2020. https://www.idsociety.org/covid-19-real-time-learning-network/vaccines
  3. Understanding mRNA Vaccines. Centers for Disease Control and Prevention. Updated December 18, 2020. Accessed December 22, 2020. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/mrna.html
  4. U.S. Food and Drug Administration. Vaccines and Related Biological Products Advisory Committee Meeting: Moderna COVID-19 Vaccine. Published December 7, 2020. Accessed December 23, 2020. https://www.fda.gov/media/144434/download
  5. Mbaeyi S. Use of Pfizer-BioNTech COVID-19 Vaccine: Clinical Considerations. Center for Disease Control and Prevention. Published December 12, 2020. Accessed December 23, 2020. https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2020-12/slides-12-12/COVID-03-Mbaeyi.pdf
  6. Implications of Emerging SARS-CoV-2 Variant. Center for Disease Control and Prevention. Updated December 22, 2020. Accessed December 23, 2020. https://www.cdc.gov/coronavirus/2019-ncov/more/scientific-brief-emerging-variant.html