Explanation: How the Moderna vaccine resists Pfizer / BioNTech

NEW YORK (Reuters) – U.S. regulators authorized Moderna Inc ‘s COVID-19 vaccine for emergency use on Friday, a week after it granted the first U.S. authorization to Pfizer Inc and the BioNTech SE coronavirus bullet.

PHOTO FILE: Coronavirus: On November 16, 2020, the US biotech company Moderna announced a vaccine against COVID-19 that is 94.5% effective. Montreal, November 16, 2020

The following is a comparison of the two vaccines with what should be expected given the availability of both:


Both vaccines use messenger RNA (mRNA) technology, which contains instructions for human cells to produce proteins that resemble part of the coronavirus. The directive stimulates the immune system, turning the body into a viral vaccine factory. Vaccines do not contain real viruses.

Both Pfizer / BioNTech and Moderna vaccines target the crown-like spikes on the surface of the coronavirus that it uses to break down healthy human cells. The spikes also give the family name the unique name of viruses.

Vaccines appear to be equally effective. The Pfizer and BioNTech vaccines were approximately 95% effective in preventing disease symptoms in its end-of-life trial, while the Moderna vaccine was approximately 94% effective.

Both are given in two doses; 21 days apart at Pfizer and 28 days apart at Moderna. Very few participants received the vaccine in all COVID-19 sick cases and almost none got sick.

Data submitted by the companies to the Food and Drug Administration suggests that they begin offering complementary protection against COVID-19 about two weeks after the recipients receive the first dose.



The main difference between the two vaccines is the temperature required to keep them stable in the long term.

Pfizer vaccine must be stored at extremely cold temperatures of less than 70 degrees Celsius (-94 Fahrenheit). Once melted, it can only be cooled for 5 days. The vaccine requires a special shipping device filled with dry ice to keep it at the right temperature.

The Moderna vaccine can be stored at a normal freezer temperature of -20 Celsius (-4 Fahrenheit) for up to six months. After thawing, it can be refrigerated for up to 30 days.


Neither of the two major clinical trials of the vaccines reversed long-term adverse effects. However, short-term side-effect profiles of vaccines are slightly different.

Although the vaccines have not been compared face-to-face, the Moderna vaccine appears to be associated with slightly more severe cases of obesity, headache and fever in the day or two after the second sight, especially in people under 65.

Although not seen in its clinical trial, the Pfizer vaccine has been linked to a few cases of severe allergic reactions as it has been rolled out in the UK and US. At least two healthcare workers in Britain and two in Alaska have reported a severe allergic reaction shortly after receiving the Pfizer / BioNTech vaccine.

The British medical regulator has said that anyone with a history of anaphylaxis, or a severe allergic reaction to a drug or diet, should not receive the Pfizer / BioNTech COVID-19 vaccine.

But the U.S. Food and Drug Administration has said it should be safe for most Americans with allergies to get the vaccine.


More data are needed to understand the effectiveness of the second vaccine in preventing the spread of viruses. While both are very effective in keeping symptoms and illnesses at bay, we do not know if they are preventing someone from becoming infected. Until that is known, experts say, masks will still be needed to make sure vaccines do not spread the virus.


At this stage, with vaccines in short supply, very few people are willing to express a preference for them. The U.S. Centers for Disease Control and Prevention has recommended that health care workers and residents in long-term care facilities should be given the first dose and most states expect to do so. to do.

Reporting by Michael Erman; Additional commentary by Julie Steenhuysen; Edited by Caroline Humer and Bill Berkrot