Pfizer and Moderna grabbed headlines, and ushered in hope, in announcing this month that each company has vaccines that preliminary data suggest to be 90-94% effective in preventing Covid-19 infections. This news is a much-needed salve to a world that has surpassed 1.37M deaths from Covid-19 since January 2020.

These genetic vaccines are different from other vaccines, like those for the flu, measles, and polio, that we’ve benefited from for decades. Traditional vaccines, like that for measles, work by injecting a small amount of a weakened form of the virus into the body. Our white blood cells sense the virus and mount a defense against it by creating specific antibodies to fight it. Our immune system has cells, called T-lymphocytes, that remember that virus, so if our body encounters measles in the future, we can make the antibodies needed to fight it immediately. These traditional vaccines take years, or decades, to create, test, and be approved, and are expensive to produce.

The Pfizer and Moderna vaccines take advantage of a different, genetic approach that uses a molecule called messenger RNA (mRNA), something you may not have thought about since high school biology class. In short, DNA is the genetic instruction manual for our bodies. mRNA makes a copy of that manual and carries it out of the cell’s nucleus to structures called ribosomes where that manual is used to make proteins. Those proteins play many critical roles in our body.

These genetic vaccines work by injecting just the mRNA instruction manual, and not the actual virus, into the human body. In fact, these vaccines use just the mRNA instructions used to create the spike protein from the coronavirus that Covid-19 uses to invade human cells.

Coronavirus Illustration

The body reacts by creating the coronavirus spike proteins, which is enough to prompt the body to produce the corresponding antibodies that fight off the coronavirus. Our memory cells will remember how to make these antibodies, so that if we are ever exposed to Covid-19, our bodies can immediately mount a defense to fight it off.

This new genetic approach to treating viruses has been studied for years and appears to have advantages over traditional vaccines. First, the process is safer because it does not involve using the actual virus. It is also cheaper and faster to produce because these vaccines are made in the laboratory, and not in chicken eggs or other mammalian cells, like traditional vaccines.

A limitation of mRNA is that it degrades easily and must be encased in fat and stored at very low temperatures. However, the Moderna vaccine can last 30 days in a refrigerator and for 12 hours at room temperature, and the preservation approaches will likely improve over time. Another limitation is that we have never used an mRNA vaccine before and do not yet have long-term data on side effects. The data collected thus far suggest a minimal side effect profile, and most side effects become evident in the first two months.

Both vaccines have already undergone preclinical testing (tested in animals to see if it produces an immune response); Phase 1 safety trials (testing in a small number of people to test safety and dosage and confirm that it stimulates the immune system); Phase 2 expanded trials (testing in hundreds of people); and Phase 3 efficacy trials (testing in thousands of people, half of whom receive placebo, to test effectiveness and safety, including rare side effects). More than 70,000 participants have taken part in the Phase 3 trials for both companies, combined. All clinical trial participants will be followed for 2 years.

Although the preliminary data suggest that both the safety and effectiveness of both vaccines are strong, we do not yet know how long each will provide protection from a Covid-19 infection. However, mRNA vaccines are thought to produce strong, long-term immunity.

Pfizer applied for emergency use authorization (EUA) through the FDA yesterday, and Moderna is likely soon to follow. If approved, genetic vaccines for as many as 35 million people may be ready by the end of 2020. Pfizer and BioNTech alone say that they could ramp up to 1.3 billion doses a year.

Although there are still several major hurdles to clear, the potential of these genetic vaccines to help address the Covid-19 pandemic on a large scale is real and may clear a path for quick and effective responses to large outbreaks in the future.

This article was written by Ellen Matloff for