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What’s the Difference Between the COVID Vaccines?

January 4th, 2021

With the approval last month of the Moderna vaccine by the Food and Drug Administration, we now have two COVID-19 vaccines available. Two more – one from Johnson & Johnson the other from AstraZeneca – are on the way and could be approved as soon as February.

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Healthcare workers, residents of nursing facilities and some first responders have already received the Pfizer vaccine, the first one approved by the FDA. Moderna has begun shipping its vaccine with the first of the 25 million initial doses administered last month.

People eager to be immunized have inundated doctors’ offices and clinics asking when the vaccine will be available. The best answer is soon.

Which one, though, will you receive? And does it make any difference?

The answer to the first question is whichever vaccine can be obtained the quickest or, in some cases, whichever your health plan recommends. It really doesn’t make any difference to you.

Both vaccines require two separate doses to reach maximum effectiveness 21 days apart for Pfizer and 28 days for the Moderna version. Both protect about equally well. The FDA data shows Pfizer is 95% effective after both doses. Moderna is 94.1%.

Unlike most other vaccines, these two vaccines use pieces of protein from the SARS-CoV-2 virus to prompt the body to create antibodies. Conventional vaccines, like the annual flu shot, are manufactured from viruses typically grown in chicken eggs. These chicken grown viruses are then killed or weakened to become vaccines.

The COVID vaccines employ messenger RNA (mRNA), a newer technology. These vaccines “teach” the body to replicate the little bit of the CoV-2 protein, which, in turn, creates an immune response causing the body to make the antibodies that provide the protection against the virus.

The most significant difference between the Moderna and the Pfizer vaccines is how they must be stored. Both can survive for a few days in standard refrigeration. For longer periods, the less stable Pfizer vaccine must be kept in ultra-low temperatures below -94 F. That makes shipping and storing Pfizer’s vaccine somewhat more complicated, especially outside urban areas where the low temperature refrigeration is not easily available.

"At the end of the day, these two vaccines are pretty similar," Dr. Thomas Russo, professor and chief of infectious disease at the State University of New York, tells Health. "Grab it while you can.”

Photo by Hakan Nural

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