Moderna vs. Pfizer: A comparison of two vaccines
A discussion about some of the key differences between the Moderna and Pfizer's Covid-19 vaccines.
On December 18th, the FDA approved the Covid-19 vaccine designed and manufactured by the American pharmaceutical company, Moderna, for emergency use authorization (EUA) in the US. EUA allows individuals who are 18+ years of age to be vaccinated against the SARS-CoV-2 virus using Moderna’s mRNA-1273 vaccine. This differs from Pfizer’s BNT162b2 mRNA vaccine, whose target population are those of 16+ years of age.
Moderna’s Covid-19 vaccine has a similar design to Pfizer’s vaccine; it’s an mRNA vaccine that codes for the spike protein, which is encapsulated by a lipid nanoparticle. However, even though both Pfizer’s and Moderna’s vaccines are similar, there are some key differences to keep in mind.
1. Moderna’s vaccine dosage is roughly 3x Pfizer’s vaccine dosage - with the same protective results.
Moderna requires two 100 mg dose shots administered through intramuscular injection, 28 days apart. In comparison, Pfizer’s vaccine requires two 30 mg dose shots administered through intramuscular injection, 21 days apart.
Even though Moderna requires a higher dosage, the vaccine has shown about the same immunological protection capacity (94.1%) as Pfizer’s (95%). If anything, there are slightly less neutralizing antibodies present after Moderna’s second dose in comparison with Pfizer.
2. Moderna’s vaccine side effects were reported to be moderately more intense than Pfizer’s vaccine.
Moderna’s vaccine side effects themselves are considered moderate - however, when compared to Pfizer’s vaccine, they are more uncomfortable.
Moderna’s Phase I/II vaccine trial participants reported mild fatigue, headaches, soreness at the site of injection, and myalgia (muscle aches) after the first dose. Slightly more severe side effects were reported after the second dose, including moderate fatigue, mild to moderate chills and headaches, and moderate redness, swelling, and soreness at the site of injection.
Still, considering these minor side effects, they are no worse than the adult Shingrix shingles vaccine side effects (i.e. soreness, swelling, fatigue, nausea, etc.). None of Moderna’s trial participants were hospitalized due to the vaccine’s side effects.
3. Moderna’s vaccine does not require extreme storage conditions, making it more accessible.
According to Moderna’s press release, Moderna’s mRNA-1273 vaccine remains stable when stored at temperatures “… 2° to 8°C (36° to 46°F), the temperature of a standard home or medical refrigerator, for 30 days.”
The vaccine’s long-term storage temperature is between -25°C to -15°C (-13°F to 5°F). At this temperature range, the vaccine vials, unpunctured, remain viable for 6 months.
Moderna’s temperature requirements are definitely an improvement to Pfizer’s vaccine storage temperature (-70°C, +/- 10°C). This less extreme temperature range will allow hospitals to store Moderna’s vaccine in their normal refrigerators. In other words, they will not need to invest in an ultra-low freezer as they would when administering Pfizer’s Covid-19 vaccine.
I feel that it is also important to note that the FDA is currently investigating reports of allergic reactions to Pfizer’s Covid-19 vaccine. At this time, research suggests that the molecule, polyethylene glycol (PEG) may be triggering the allergic reactions. Both Pfizer’s and Moderna’s vaccine contain this molecule.
The spike mRNA is encapsulated by a lipid nanoparticle. This nanoparticle is connected to the molecule, polyethylene glycol, which helps increase the particle’s lifespan.
PEGs are used in everyday products, such as toothpaste, shampoos, detergents, and even as laxatives.
All vaccines have the potential to provoke allergic reactions in some people, however, it is extremely rare. The FDA is thoroughly reviewing the allergic reaction reports and they suggest that those who have a history of allergic reactions in general should not be vaccinated at this time. Pfizer also clearly warns those who are knowingly allergic to the vaccine ingredients to refrain from being vaccinated.
Additional Readings:
Pfizer’s vaccine raises allergy concerns - Science magazine
Moderna Vaccine Fact Sheet - EUA restrictions
Pfizer-BioNTech COVID-19 Vaccine EUA Fact Sheet for Recipients and Caregivers