Reprinted from the Spring 2021 Issue of The Ohio Family Physician
By: Sanford R. Kimmel, MD, FAAFP, FAAP, Emeritus Professor of Family Medicine at the University of Toledo College of Medicine
Composition of the COVID-19 Vaccines
Multiple vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and/or COVID-19 disease are in development, but two are now available in the United States under Emergency Use Authorization from the Food and Drug Administration. They are the BNT162b2 vaccine created by BioNtech and Pfizer, and the mRNA-1273 vaccine developed by Moderna and the Vaccine Research Center at the National Institute of Allergy and Infectious Diseases. Both use lipid-encapsulated modified messenger RNA (mod-mRNA) to encode for the full-length spike protein on the surface of the virus. Neither of these vaccines contains live or attenuated virus.
Efficacy of the Vaccines
Two injections, 21 days apart, of the BNT162b2 vaccine were given to 18,556 persons compared to 18,530 who received placebo. Eight cases of COVID-19 occurred at least seven days after the second dose in vaccine recipients without prior evidence of SARS-CoV-2 infection and 162 cases occurred in the placebo group with a calculated efficacy of 95%.1,2 Following the first dose of the Pfizer-BioNtech vaccine, but before the second dose, there were 39 cases of COVID-19 in the vaccine group versus 82 cases in the placebo group. There was one case of severe COVID-19 in the vaccine group and nine in the placebo group. Calculated vaccine efficacy was 52% with protection starting as early as 12 days after the first dose.1,2
Two injections, 28 days apart, of the Moderna vaccine were given to 14,134 persons negative for SARS-CoV-2 compared to 14,073 who received placebo. Eleven cases of COVID-19 occurred at least 14 days after the second dose in the vaccine group versus 185 cases in the placebo group for a vaccine efficacy of 94.1% .3,4 Vaccine efficacy was 95.6% in persons aged 18 to 64 years old versus 86.4% in persons 65 years or older.3,4 All 30 cases of severe COVID-19 were in the placebo group.3,4
Known Vaccine Adverse Events
Pain at the injection site was the most common local reaction to either vaccine occurring in 80% or more of recipients, but was less frequent in recipients older than 55 or 65 years old.2,3 Redness and swelling occurred less frequently, but was more common after the second dose of both vaccines.2,3 Fatigue, headache, myalgias, and arthralgias were also common with both vaccines, especially after the second dose.2,3 Fever and chills were more common in younger participants than older ones after the second dose.2,3 Cases of Bell’s palsy have been reported after both vaccines, but a causal relationship has not been determined.2,3 Severe allergic reactions (e.g., anaphylaxis) have been reported and are estimated at 11.1 cases per million doses for the Pfizer-BioNTech vaccine.5 No data is yet available for the Moderna vaccine. Contraindications to both vaccines include anyone with a history of severe or immediate allergic reactions to a prior dose of the vaccine or their components including polyethylene glycol (PEG) or polysorbate, which might cross-react with PEG.6 Persons with a history of other severe allergies should be observed for 30-minutes in an area where severe allergies can be treated.
Serious vaccine adverse events including administration errors should be reported to the Vaccine Adverse Events Reporting System (VAERS) or by calling 800.822.7967.2,3 The smart-phone tool, V-safe.2,3
Vaccine Storage and Administration
The Pfizer-BioNTech COVID-19 vaccine is stored at -70oC (-94oF). Each 5-dose vial is diluted with 1.8 ml of sterile 0.9% sodium chloride and mixed by gently inverting 10 times. Each 0.3 ml dose contains 30 mcg of mod-mRNA and is given intramuscularly (IM). The second dose is given in 21 days.2 The Moderna COVID-19 vaccine multiple-dose vials are stored frozen between -25oC to -15oC (-13oF to 5oF), but can be refrigerated between 2oC to 8oC (36oF to 46oF) for 30 days prior to first use. Before using, the suspension should be thawed in the refrigerator for 2.5 hours, stand at room temperature for 15 minutes, and then swirled gently prior to and after each withdrawal. It is dosed at 0.5 mL IM with the second dose given at 28 days.3 After opening the vials for both vaccines, they should be discarded after six hours.2,3 The vial stoppers of both vaccines do not contain latex.2,3 The Centers for Disease Control and Prevention now states that “if it is not feasible to adhere to the recommended interval, the second dose of Pfizer-BioNTech and Moderna COVID-19 vaccines may be scheduled for administration up to six weeks (42 days) after the first dose.”6
Vaccine Contraindications and Precautions
The vaccines are not considered interchangeable. The second dose of the vaccine should be the same as the first. If a different mRNA vaccine is given for the second dose, it should not be repeated.
There is limited data on the safety of COVID-19 vaccines in pregnant or lactating women. The use of the vaccine in this population should be based on the level of risk based on community transmission, occupational exposure, and personal risk factors.2,3
Some Unanswered Questions
The level and duration of protective immunity after natural infection or vaccination are not known. It is not known if widespread vaccination will result in herd immunity.7
References available on the OAFP website.
All data is reported as of January 23, 2021.