Comparing the Covid Vaccines



We are now blessed with not one but two Covid vaccines approved by the FDA. The first was produced by Pfizer/BioNTech and the second by Moderna. How do they compare? Helen Branswell gives us this comparison in Health:

Target Population

The Pfizer vaccine is authorized for use in people aged 16 years and older. The Moderna vaccine is authorized for use in people aged 18 years and older. Currently, Moderna is being tested in 12 to 17-year-olds.

Vaccine Efficacy

The Pfizer vaccine showed 95% efficacy seven days after the second dose. There were no differences in protection across age groups and racial and ethnic groups. The Moderna vaccine showed 94.1% efficacy fourteen days after the second dose. It is also equally effective across age, racial and ethnic groups.

Number of doses/Amount of vaccine

Both vaccines require two doses for effectiveness. The second, or booster dose, is given in 21 days for the Pfizer vaccine and in 28 days for the Moderna vaccine. The Pfizer dosage is 30 micrograms and the Moderna dosage is 100 micrograms. This may result in slightly more discomfort at the injection site for the Moderna vaccine.

Side Effects

Both vaccines are considered reactogenic. That means they may trigger a range of transient effects in a significant number of recipients. The most common side effects are injection site pain, fatigue, headache, muscle or joint pain. A few have reported fever. Side effects are more likely after the second dose. Young people have reported more side effects than older adults, possibly because their immune systems mount more robust responses. A very small number (six) of strong allergic responses have been reported with the Pfizer vaccines that were not seen at all in the trials. None have been reported yet with the Moderna vaccine.

Safety for Pregnancy

Neither vaccine has been tested in this population group. However, both vaccines report no complications in pregnant animal studies.

Storage Requirements

This is perhaps the most significant difference between the two vaccines. The Pfizer vaccine requires storage at -94 degrees Fahrenheit. This means ultra-cold storage freezers that must be topped out with dry ice every five days. This makes it impractical for doctors’ offices. The Moderna vaccine requires storage at -4 degrees Fahrenheit, suitable for a regular refrigerator freezer. This makes it suitable for doctor’s offices and neighborhood pharmacies.

Minimum Purchase Order

Pfizer requires a minimum purchase order of 975 doses. This makes it suitable for large teaching hospitals, but possibly not for small institutions. The Moderna vaccine requires a minimum purchase order of 100 doses, making it more suitable for doctors’ offices and pharmacies.

There you have it, two effective vaccines with minimal side effects. Both will require two doses but both will provide excellent protection against the Covid virus. The Moderna has some advantages in storage, shipping, and distribution, making it more suitable for doctors’ offices and pharmacies. The Pfizer vaccine will probably be limited to large institutions.

It doesn’t really matter which vaccine you take; just take the vaccine!


  1. Thanks for information with which I feel confident.

    Comment by Allen Higginbotham on January 7, 2021 at 7:57 am

  2. It is my pleasure to provide useful information we can rely on. Glad to know it is appreciated.

    Comment by Robert Roberts on January 8, 2021 at 9:36 am