What You Need to Know about the Janssen COVID-19 Vaccine

Betty Chaffee/ March 4, 2021/ Coronavirus, COVID-19, immunization, vaccines/ 4 comments

A third COVID-19 vaccine is now available!

The Food and Drug Administration (FDA) gave emergency use authorization to a vaccine produced by Janssen, the pharmaceutical branch of Johnson & Johnson, last weekend. This is great news. A third vaccine will increase the overall supply substantially, and we'll be able to get more people vaccinated quickly. The new vaccine is already being shipped so it's likely to be availabile in our community soon.

I'll summarize the important information about the Janssen vaccine in this short post. For those of you who follow BetterMyMeds on Facebook, watch for a live video presentation about the vaccine in the next week or so!

How is the Janssen vaccine different from the mRNA vaccines by Pfizer and Moderna?

The newest vaccine is what’s called a “viral vector” vaccine. It starts with a common virus, known as an adenovirus, that we've all encountered in the environment. Researchers modified the adenovirus so it can't multiply inside the body to cause disease. It carries a bit of DNA that contains the code for the spike protein on the SARS-CoV-2 virus. Once that genetic material gets into the human cell, the process of transcription results in production of mRNA.  From there it works very much like the mRNA vaccines we've already talked about. The mRNA teaches our own cells how to produce proteins exactly like the spike protein on the SARS-COV-2 virus. The body quickly recognizes that protein as an outsider and begins making antibodies against it. If the SARS COV-2 virus invades later, our bodies are ready to fight it off.

The great thing about this inactivated adenovirus is that it's a safe vector. It just gets into cells and delivers the genetic material without causing harm. The DNA doesn’t integrate with our own cells' DNA, either, so it can't alter the genetic makeup of our cells.

mRNA technology hadn't been used in a medicine or vaccine until the COVID-19 vaccines were authorized. But viral vector technology has already been in clinical use (though not in the US) as a vaccine against the Ebola virus. So there’s a fair amount of experience using it in a major health crisis.

The Janssen vaccine is also different in that it’s authorized as a single-dose rather than a two-dose series. You'll have full immunity just two weeks after one dose --  much sooner than full immunity from an mRNA vaccine. And it doesn’t require freezer temperatures for storage. That makes it a lot easier for doctor’s offices, pharmacies, and drive-through or pop-up vaccination clinics to store. It'll be much easier get vaccine to many people really quickly.

What are the similarities between the three available vaccines?

The best news is that all three vaccines provide excellent protection against symptomatic COVID-19. The small number of patients who did come down with COVID-19 after vaccination were well protected from severe disease. Very few needed to be hospitalized, and none died. In fact, the Janssen vaccine study included groups from South Africa and Brazil who were exposed to variants of the SARS-COV-2 virus and were still well protected. 

Side effects from the new vaccine are similar to the mRNA vaccines. Headache, fever, stomach upset, pain at the injection site, and fatigue were relatively common. Typically those side effects lasted only a day or two. And like the mRNA vaccines they happened more often in younger individuals than older individuals. The vaccine caused no serious health problems, including serious allergic reactions. But you'll still need to be watched for 15-30 minutes after vaccination, just to be safe. Information about safety and efficacy is still being collected in the ongoing studies. And don't forget to sign up for the V-Safe program when you get vaccinated so you can help provide information too!

The only reason not to be vaccinated with the Janssen vaccine is if you’re allergic to any of the components in the vaccine. If you're pregnant, or have an immune disease or other health condition, you're still a candidate for this vaccine.

But which vaccine is the best?

Now there are three vaccines available. You may wonder if you need to make a choice about which one to get. Because all three provide excellent protection from disease and have proven to be safe, here's the important takeaway:

The best vaccine is the first vaccine available to you!

The quicker we can get lots of people vaccinated, the safer we’ll all be. 

As always, we welcome your comments and questions below. Or contact us at BetterMyMeds anytime! And don't forget to watch for the announcement of our live presentation on Facebook (you can also watch the recording later if you miss it).


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About Betty Chaffee

Betty Chaffee, PharmD, is owner and sole proprietor of BetterMyMeds, a Medication Management service devoted to helping people get the maximum benefit from their medications.


  1. On Jan. 11, I was given the first Pfizer vaccine shot. My second shot was scheduled for Feb. 1. Michigan Heart scheduled for a heart procedure on Feb. 2. I called Michigan Heart to ask about getting my second shot.. They told me that I should not get that shot. The heart procedure (replacing my aortic valve) was rescheduled for Feb. 9. I went into St. Joes ,(Ann Arbor) that day and had the valve replaced. The surgeon did not want me to get the shot until I met with T. Hall on Feb. 19.. I live in the Cedars of Dexter which is a part of the UMRC housing . Our shots were given only on Jan.11 and Feb. 1 through special arrangement with the Washtenaw County Health Department. I have registered with the County health department but I have no way of knowing where I will be on their list (I am 84 years old). Do you have any suggestions about how I can get my second shot?

    1. Hi Dave,

      Wow, it sounds like you had a “perfect storm” of events leading to this problem. Since second doses are scheduled at the time of the first dose, this kind of thing doesn’t happen often. But you’re definitely not alone — unexpected events like these do happen and can leave people like yourself wondering what to do.

      Now that there are three different vaccines out there, simply signing up with a vaccine provider may not get you what you need, since most providers don’t always know in advance what type of vaccine they’ll get. But definitely stay on the County registration, and you could put your name on the list at Meijer, Rite Aid, or Jensen’s Community Pharmacy in Dexter. But here’s the good news – in an educational session about the new Janssen vaccine they addressed this specific problem. It turns out that if a two-dose series of Pfizer or Moderna can’t be completed, a person can be vaccinated with just one dose of the Janssen vaccine. In that case, the Janssen vaccine is NOT considered to be the second dose of a two-dose series, rather it’s considered to be the only vaccine conferring immunity. So you can get that vaccine if it’s offered and you’ll be all set!

  2. Today (3-5-21) phone call from my doctor’s office informing me that I will be getting a phone call sometime next week about when and where I can get my second shot. Thank heavens for that news.

    1. The system works!

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