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Pfizer BioNTech and Moderna COVID19 Vaccines

The Food and Drug Administration has issued an Emergency Use Authorization for the BioNTech/Pfizer’s BNT162b2 and Moderna’s mRNA-1273 vaccines. The BioNTech vaccine is administered intramuscularly (IM) as two 30 ug doses 21 days apart, while the Moderna product is given IM as two 100-ug doses 28 days apart. The Pfizer-BioNTech COVID-19 vaccine was approved for persons aged ≥16 years for the prevention of COVID-19, while the Moderna vaccine was approved for persons 18 years and older. Both vaccines showed good efficacy for individuals 65 and older.

Both vaccines consist of a nucleoside-modified mRNA encapsulated in a lipid nanoparticle. The modified mRNA in these vaccines codes for a trimeric version of the receptor binding domain of the spike glycoprotein of SARS-CoV-2. The chemical formulation of these vaccines has been almost fully disclosed. They incorporate a trinucleotide cap 1 analog ((m27,3!-O)Gppp(m2!-O) ApG), contain N1-methylpseudouridine instead of uridine, and encode an optimized (P2-mutated) full-length S glycoprotein encapsulated in lipid nanoparticles(LNPs) containing polyethylene glycol and cholesterol. The Pfizer BioNtech LNP also contains (4-hydroxybutyl)azanediyl) bis(hexane-6,1-diyl)bis(2-hexyldecanoate) and 1,2-distearoyl-sn-glycero- 3-phosphocholine, whereas Moderna’s LNP contains SM-102 (most likely heptadecan-9-yl 8-((2-hydroxyethyl) (6-oxo-6-(undecyloxy)hexyl)amino) octanoate) and 1,2-dimyristoyl-rac-glycero- 3-methoxypolyethylene glycol-2000 (PEG).

Clinical trial data indicated that both the BioNTech and Moderna vaccines were very effective in inducing immunity to SARS-CoV-2. Of the 20,033 people who received the Pfizer BioNTech vaccine, efficacy outcomes one week after second dose were 95%. In the 13,218 participants receiving two doses of Moderna’s vaccine, efficacy was 93.4% for people 18 to 64 years old and 86.4% for those ages 65 and up.

According to a recent study published in the New England Journal of Medicine, the Pfizer BioNTech vaccine does not begin providing protection until 12 days after the first shot and it takes a few weeks for the first dose to reach 52% effectiveness. One week after the second dose, effectiveness reaches 95%. Moderna has reported its protection rate reaches 51% two weeks after the first shot. Two weeks after the second shot, the effectiveness rate is 94%.

Adverse events following administration of the vaccines are submitted to the Vaccine Adverse Event Reporting System. For both products, adverse events have included fatigue, fever, headache, myalgia, arthralgia, pain/swelling at the injection site, lymphadenopathy, nausea, erythema, Bell’s palsy and appendicitis.

CDC reported on January 6 that 21 of the 1.9 million people who had received the Pfizer BioNTech vaccine during the first two weeks of vaccination experienced severe allergic reactions. Of the 21 cases studied, 17 of the people had a documented history of allergies or allergic reactions, and seven had a history of anaphylaxis. Nineteen of the 21 patients who developed anaphylaxis were women and the median age was 40. Almost all of the patients developed symptoms within 15 minutes of receiving the vaccine. Nineteen patients were treated with epinephrine. Four patients required hospitalization and 17 were treated in an emergency department. Twenty of the 21 patients have fully recovered. No deaths have been reported.

CDC has also reported there had been one case of anaphylaxis after administration of the Moderna vaccine. NIH is trying to determine which component of these vaccines is causing anaphylaxis. One suspected component is polyethylene glycol, which is widely used in medicines, cosmetics and other household products.

At this early stage, some important unanswered questions remain. First, data on hospitalizations and deaths are limited at this time, but a vaccine that effectively prevents symptomatic infection is expected to also prevent patients from becoming severely ill. Second, it remains unclear whether the vaccine can prevent people who show no or only very mild symptoms of COVID19 from spreading the coronavirus to others. In order to determine this, trial participants would have to be repeatedly tested for the virus. Third, trial participants will need to be followed for much longer to determine the duration of the antibody and how often people may need to be vaccinated.


FDA Briefing Document Pfizer-BioNTech COVID-19 Vaccine, Vaccines and Related Biological Products Advisory Committee Meeting December 10, 2020

FDA’s EUA Letter to Pfizer on December 11, 2020

Oliver S, Gargano J, Marin M, et al. The Advisory Committee on Immunization Practices’ Interim Recommendation for Use of Pfizer-BioNTech COVID-19 Vaccine — United States, December 2020. MMWR Morb Mortal Wkly Rep. ePub: 13 December 2020. DOI: icon

Messengers of Hope, Nature Biotechnology, published online December 29, 2021,

Polack FP et al. Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine. N Engl J Med 2020; 383:2603-2615.

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