The 2 FDA-approved COVID-19 vaccines are similarly effective but also very different in a number of ways that will affect distribution.
The US Food and Drug Administration has approved for emergency use 2 vaccines against the coronavirus disease 2019 (COVID-19), one from Pfizer-BioNTech (December 11, 2020) and the other from Moderna (December 18, 2020).
The vaccines are very similar in terms of efficacy and both require a priming dose followed by a booster a few weeks later. But there are vast differences in aspects like cold chain storage and even minimum purchase amount required that are already impacting who likely will receive which vaccine.
The short slide show below summarizes a comparison of features published on the web site STAT.
Efficacy. Essentially equivalent, based on early stages after vaccination.
Pfizer: 95%efficacy at preventing symptomatic COVID-19 infection, measured beginning 7 days after second dose.
Moderna: 94.1% efficacy at preventing symptomatic COVID-19 infection, measured beginning at 14 days after second dose.
Efficacy. What we don’t know.
Does either vaccine prevent asymptomaticSARS-CoV-1 infection?
Can vaccinated individuals transmit virus if infected but asymptomatic?
Doses/amount of vaccine per dose. Both require 2 injections – priming and booster.
Pfizer: 21 days between shots, 30 µg each.
Moderna: 28 days between shots, 100 µg each.
Side-effect profile. Both are reactogenic.
ACIP advises hospitals to stagger administration among departments to minimize staffing issues. Most common: injection site pain, fatigue, headache, myalgias, arthralgias; fever has been reported. More common: after second dose and in younger vs older adults.
Safety in pregnancy/lactation. Neither vaccine has been studied in these groups.
Moderna: Completed animal studies and saw no concerning evidence of harm.
Pfizer: Interim data from animal studies show no concerning signs.
Authorizations for both state data are insufficient to gauge safety in these groups.
Storage requirements. Both vaccines require elaborate cold chain storage.
Moderna: must be shipped at -4°F, the temperature of a regular domestic refrigerator freezer.
Pfizer: must be shipped at -94°F; requires special, ultracold freezers not found in average offices, pharmacies.
Stability after thawing is significantly better for Moderna product.
Durability of protection. Currently this is an unknown.
Long-term surveillance is required to understand how long protection will last. Antibody levels will be assessed via periodic blood draws from volunteers.
Reports that large numbers of immunized persons are contracting COVID-19 would indicate the need for booster shots at some defined interval.