Over this past weekend, the FDA granted emergency authorization to a 3rd COVID-19 vaccine from Johnson & Johnson (J&J).  This vaccine is a single shot in the arm – a one and done. So, you might be wondering how this one compares to the two we already have from Pfizer-BioNTech and Moderna.  Before getting into the weeds, note that it’s wise to avail yourself to whatever vaccine becomes available to you.  As Yogi Berra would say, “If you see a fork in the road, take it!”  Let’s break it down.

Comparing the newcomer with the previous two is a little challenging, because it’s a different type of vaccine, yet, like apples and oranges, it provides what we need. While the Pfizer and Moderna varieties are mRNA vaccines, J&J’s is an adenovirus vaccine.  This means that they work by different mechanisms in the body.  You’re already quite familiar with drugs that work by different mechanisms or have different molecular formulations-yet achieve the same results-if you’ve ever taken Tylenol (acetaminophen), aspirin (acetylsalicylic acid), or Aleve (naproxen) for pain.  Did it matter to you which one you took as long as your ache went away?

What is an adenovirus vaccine?  Adenovirus vaccines are the type we’re already accustomed to using, because they’ve been used for many flu vaccines. Adenovirus vaccines are double-stranded DNA vaccines that use a modified adenovirus to target those coronavirus spikes.  Let’s circle back to a few terms: adenovirus, double-stranded DNA, and modified adenovirus.  Adenoviruses are a group of DNA viruses that were first discovered in adenoid tissue.  The word part “adeno-” means gland, and adenoid tissue is found in lymphatic tissues, which play major roles in our immune response.  You’ve heard of “adenoids,” those inflamed tonsils at the back of the throat that become enlarged with an infection.  Guess what?  Those tonsils are masses of lymphatic tissue, and if they become enlarged, your immune system is just doing its job.  These adenoviruses typically cause respiratory infections, like the flu.  Double-stranded DNA is our next term.  DNA carries our genetic information, and each molecule of DNA has two coiled strands.  RNA, in comparison, is single-stranded. Our last term, “modified adenovirus” requires a little focus.  Take a sip of your coffee.  Modified means that the virus has been manipulated in the lab to serve as a vector. A vector is just a fancy term for vaccine delivery device.  Now it’s called an “adenovector vaccine,” which won’t harm you, but can mount an immune response against the coronavirus.

How does the new vaccine work?  When you get the vaccine, your body starts making antibodies to coronavirus.  These antibodies will then become memory cells.  (That’s actually their biological name.). They are called memory cells because they remember a virus they have seen before.  That means if they encounter the coronavirus in the future, they know what to do:  they pull out those antibodies, mount an immune response, fight off the virus, and you live happily ever after.

To understand how these vaccines differ, you need a short biology lesson explaining how DNA and RNA are related. Stay with me here, and I’ll give you the really simple version. If you want the lecture, come to physiology class.  Here goes: DNA is a molecule that has the instructions for making proteins, but it needs mRNA to actually make those proteins. Think of DNA as the code, mRNA as the recipe, and protein as the product. It’s the cellular version of the telephone game, and the 3-step pathway goes like this:

Step one = DNA, step two = mRNA, step three = Protein


How do the three vaccines compare?  All are effective!  Ongoing trials, incoming data from vaccinated populations, and variant strains will continue playing a role in tweaking and dosing. It’s science in real time with real people.  Here’s a quick summary:

Johnson & Johnson

– Type: DNA vaccine: begins at step one; code is already there –> tells mRNA to make coronavirus spike protein–> activates immune response and antibodies

–  Dosage:1 dose

– Storage: standard refrigerator for 3 months


-Type: mRNA vaccine: begins at step two; recipe is already there to make coronavirus spike protein –> activates immune response and antibodies

-Dosage: 2 doses, second dose 21 days after first

– Storage: ultra-cold for extended periods, standard freezer for 2 weeks, refrigerator for 5 days after thawing, cannot be refrozen


-Type: mRNA vaccine: begins at step two; recipe is already there to make coronavirus spike protein –> activates immune response and antibodies

– Dosage: 2 doses, second dose 28 days after first

– Storage: standard freezers, refrigerator for 30 days after thawing, cannot be refrozen

The worldwide scientific community came together to develop these vaccines to eradicate the virus.  Keep in mind that in order for COVID-19 to go away, people across the globe – not just in the United States-have to be vaccinated.  And, we have to achieve herd immunity.  While we’ve had to limit our togetherness, we are truly in this together.