A Tale of Two Viruses: Johnson & Johnson’s COVID-19 Vaccine

The company that brought you Johnson's Baby Powder threw its hat in the COVID-19 ring and produced the US's third vaccine option, a viral vector vaccine. But how does it work?

If we called 2020 the Year of the Lockdown, let’s call 2021 the Year of the Vaccine.

As of this writing, the number of folks in the US having gotten at least one shot to protect themselves against the SARS-CoV-2 virus is over 158 million. Most Americans have received either Pfizer or Moderna vaccines, mostly because these two mRNA vaccines were the first out of the starting gate.

However, the US has a third horse in the race against COVID-19, and that horse is the Johnson & Johnson vaccine.

Yes, this is the company whose Q-tips you’ve probably used to clean your ears, or whose baby powder you’ve dusted on your tiny humans at home.  

J&J received its approval for distribution a couple months after Pfizer and Moderna vaccines got theirs. And although in some ways the vaccine functions similarly to the mRNA vaccines, it’s just different enough to warrant its own article.

Why is that? The nutshell version:

The Johnson & Johnson vaccine uses a virus to deliver information from the SARS-CoV-2 virus to your body so it can mount a defense against SARS-CoV-2.

Sound crazy? Yeah, it is. In the best sense of the word.

So… as part of my COVID-19 series, let’s talk about the inner workings of the Johnson & Johnson COVID-19 vaccine.

Facts About the Johnson & Johnson COVID-19 Vaccine

Here are some interesting facts about the J&J shot:

  • The FDA issued the emergency use authorization (EUA) for this vaccine on 2/27/2021, about two months after Pfizer and Moderna shots received approval.
  • The J&J vaccine is a viral vector vaccine, similar to but still different from Pfizer and Moderna mRNA vaccines.
  • Unlike Pfizer and Moderna shots, which require two doses, the J&J vaccine only requires one.
  • Based on clinical trial data: overall efficacy is 66% (72% in the US) in preventing mild to moderate COVID-19 (lower than that of Pfizer and Moderna), but considerably higher in preventing severe disease. It offers complete protection against COVID-19-related hospitalization and death for 28 days after vaccination.
  • This vaccine provides protection against new viral variants, including the South Africa, United Kingdom, and Brazil variants.
  • Unlike Pfizer and Moderna vaccines, the J&J vaccine used fetal cell cultures to develop and manufacture the vaccine. However, the vaccine does NOT contain these fetal cells.
  • The J&J vaccine is stable at regular cold temperatures for a longer period, making it less difficult to deal with than Pfizer and Moderna vaccines.
  • J&J vaccine distribution halted for 10 days in the US due to 15 people suffering a rare but severe blood clotting disorder. They resumed distribution when it was determined that the risks fell within acceptable limits (15 out of 7.2 million shots given). However, women 18-49 should be aware of this rare side effect before choosing this vaccine.

Before I go into how this vaccine works, let’s make an important distinction.

Two Types of Vaccines

Most people tend to think all vaccines are basically the same: they contain some version of the pathogen we want to protect ourselves against, and upon injection our immune systems begin developing antibodies to fight the pathogen, right?

In some cases, yes, but not all.

Today’s vaccines contain either:

  • An antigen (e.g., weakened or inactivated pathogen, pathogen parts, or pathogen toxins)
  • The instructions to make an antigen

There are many types of vaccines, which I summarize briefly here. The first four categories all contain antigen of some kind:

  1. Inactivated vaccines contain the pathogen of interest, but it’s been killed. Examples include flu, rabies, and hepatitis A.
  2. Live (attenuated) vaccines include live pathogen, but the germ has been weakened considerably. Examples include chickenpox, measles, and many of the other shots we receive in childhood.
  3. Subunit, recombinant, polysaccharide, and conjugate vaccines have parts of the pathogen (rather than the whole thing), and those parts serve as antigens. Whooping cough and shingles are examples.
  4. Toxoid vaccines include a toxin emitted by the pathogen as antigen. Tetanus and diphtheria shots are toxoid vaccines.

The latter two categories, on the other hand, contain only the instructions for your body to create the antigen.

  • Messenger RNA (mRNA) vaccines include a segment of messenger RNA that provides the instructions to make a piece, and only a piece, of the pathogen. Pfizer and Moderna COVID-19 shots are the first two of this kind to be approved and distributed to the public.
  • Viral vector vaccines use a “vector” (i.e., a delivery device), usually a modified virus, to deliver instructions to create the antigen. Examples include the Ebola vaccine and, of course, the Johnson & Johnson COVID-19 vaccine.

The difference between mRNA and viral vector vaccines is the “providing instructions” part. We learned one way to provide said instructions when I explained how the Pfizer and Moderna mRNA vaccines work.

Now we’ll learn how Johnson & Johnson does it.

What Exactly is a Viral Vector?

Like mRNA vaccines, viral vector vaccines provide the genetic instructions to create an antigen that signals our immune systems to develop antibodies. However, instead of delivering the instructions via a fragment of mRNA, they do so through a viral vector.

But what is a viral vector?

At its most basic, a viral vector is a mechanism to deliver genetic material into cells. The vector, a modified virus, contains the genetic code needed to create the necessary antigen.

Viral vectors play an important role in the development of gene therapies. Scientists also use them in molecular biology research.

Like mRNA vaccines, scientists have studied viral vector vaccines for decades. But only more recently have viral vector vaccines received approval for use with the public.

Types of viral vectors include:

  • Adenoviruses
  • Retroviruses
  • Lentiviruses
  • Adeno-associated viruses

The J&J vaccine employs an adenovirus, a class of viruses responsible for conditions such as the common cold and pink eye.

How Viruses Work

Here’s the truth: viruses are sneaky little bastards.

They invade our cells and commandeer our genetic machinery so that we make more viruses. Yeah, they use us to make more of them, and make us sick in the process.

To understand this process, remember that DNA codes for RNA (transcription), which then codes for protein (translation):

DNA RNA protein

Viruses infiltrate this process and use it to replicate its own genetic code, so it can multiply and spread through our bodies.

The good news is viral vector vaccines capitalize on this fact and use it to our advantage. But how?

How the Johnson & Johnson Vaccine Works, Step by Step

The steps are:

  1. Isolate the gene for the SARS-CoV-2 spike protein. The SARS-CoV-2 virus that causes COVID-19 has a gene that codes for a spike protein, those funny-looking spikes you’ve seen in pictures of the virus. Scientists identify and isolate that gene from the virus’s genome.
  2. Insert the gene into a viral vector. The J&J vaccine uses an adenovirus (known as Ad26) that’s been altered so it won’t cause disease. Scientists insert the spike protein gene into the adenovirus genome.  
  3. Deliver the adenovirus. The altered virus containing the SARS-CoV-2 spike protein gene is injected, via vaccine, into a patient. It then enters our cells.
  4. Transcription and translation. The cell recognizes the gene for the spike protein and our bodies create that protein, and only that protein. This protein serves as the antigen.
  5. Cue immune response. As with all antigens, your immune system detects this foreign body and begins developing antibodies.

To put it differently, the Johnson & Johnson vaccine behaves like a Trojan horse. The Greeks used a large, hollow horse to hide themselves so they could enter the gated city of Troy during the Trojan War. It was presented as a gift, but in reality made it so the soldiers could easily invade the city.

Viral vector vaccines do the same thing: they use a virus to sneak into our bodies the instructions to make our own little army to fight off the SARS-CoV-2 virus.

Hey, if viruses can be sneaky bastards, so can we.

Replicating Versus Non-Replicating

There are two kinds or viral vector vaccines: replicating and non-replicating. The J&J vaccine is non-replicating, which means it only produces the antigen and does not produce new viral particles.  

That’s all, folks. Please leave a comment, and if you want to know when the Rogue Scientist publishes a new article, sign up for my email list.

Related Articles and Resources

Health and Human Services: Types of vaccines

North Dakota Dept. of Health: J&J vaccine fact sheet

J&J clinical trials: summary and publication

J&J vaccine trials: trial details

GAVI: The Vaccine Alliance: How viral vector vaccines work

The New Kid in Town: How Exactly do mRNA Vaccines Work, Anyway?

The Rogue Scientist

Christie Hartman is a writer and scientist specializing in science-based health. A biology major as an undergrad, she completed her PhD in behavioral genetics at the University of Colorado Boulder. Before starting her writing career, she worked as a scientist and professor at CU’s School of Medicine, where she studied the genetic contributions to substance abuse and antisocial behavior.

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