Does this Vaccine use Genetic Material Too?‘
Unlike the mRNA vaccines by Pfizer and Moderna, the Johnson and Johnson (J&J) vaccine uses DNA to tell our bodies to make the spike protein. The J&J vaccine is an adenovirus based vaccine. That means that scientists took a human adenovirus, Adenovirus 26, modified it, and added a gene for the spike protein to it. Adenoviruses are pretty common, and cause things like colds or flu-like illnesses. This one has been modified so it can’t replicate or cause human illness, but it can make the coronaviruses spike protein.
Viruses are like little machines and their job is usually to get into cells and use the cell’s machinery to make copies of themselves. That’s their only job: cell entry and reproducing themselves. For a vectored vaccine, scientists use this against another virus. Viruses already know how to get into a cell, but scientists modify can modify certain viruses to reproduce an antigen, like the spike protein, instead of themselves. So, the virus infects your cells, as viruses do, and instead of reproducing itself, it has your cells make spike protein. Just as in the Moderna and Pfizer vaccines, your cells are making the spike protein. The virus vector just helps the DNA get in.
Once the spike protein is made, your body reacts to it much like the two other EUA coronavirus vaccines do. The immune system sees the spike protein, makes antibodies and immune cells to fight it, and the adenovirus gets taken away by them too. The mRNA virus FAQ has more on the immune system and the spike protein. The Johnson & Johnson vaccine uses double-stranded DNA to code for the spike protein, so it does skip the translation step. It also has a virus to help it into the cell, so it doesn’t need complexing agents than the Moderna and Pfizer vaccines do. The PEG in the Moderna vaccine, its complexing agent, is one possible allergen.
Adenoviruses are actual ideal vectors. They are easy to manipulate. They are capable of infecting many types of cells. They can induce both CD4+ T cell- and CD8+ T cell-mediated immune responses. There is also a chimp adenovirus vaccine in the pipeline, but the J&J one is human. Scientists have been working on adenovirus vectored vaccines since the 1970s.
Johnson and Johnson Experience
J&J has a lot of experience with adenovirus vectored vaccines. They have been researching them for decades and released one in July of 2020 for ebola. Prior to approval, there were actually two adenovirus Ebola vaccines used in a couple hundred thousand people in the ebola outbreaks in West Africa and the Democratic Republic of Congo. They have trials on adenovirus vectored vaccines for HIV and Zika Virus as well.
Why Can it Be Refrigerated and the Others Need to be Frozen?
mRNA is pretty fragile. That’s why those vaccines have to be frozen and handled with care. J&J uses DNA, which is more resilient. The adenovirus helps protect it too. It still needs to be handled with care, but it can stand up to higher temperatures and a bit rougher handling.
What Happens to the Adenovirus?
The adenovirus has been crippled. It can’t reproduce itself. Your immune system will react to it like it does to any other new virus and remove it from your system. It won’t stay around forever and you won’t produce spike protein forever.
What if I’ve Been Exposed to an Adenovirus Before?
Most of us have been exposed to an adenovirus before. If you’ve been exposed Ad26 or one that looks too close to it, your immune system may destroy the vaccine before it has a chance to work. Ad26 antibodies are uncommon in Europe and the US, but more common in some other countries.
There is some concern that being exposed to the vector once would ruin a boosted dose, and AstraZeneca’s chimp adenovirus vaccine had some controversy. They accidentally gave some participants half a vaccine dose for one shot. Those patients did better than the people who had two full doses. There was some concern that maybe the first dose canceled the second because the immune system destroyed the vector before it entered the cell.
Russia’s Sputnik vaccine actually had this very concern and used two different adenovirus. They used one virus for the original shot, and a different one for the booster dose. J&J’s Zabdeno, the ebola virus vaccine, is actually 2 doses that use a different vector too.
Johnson and Johnson claims that one reason they chose Ad26 is that it’s not as immunogenic as other adenovirus vectors (like Ad5). That means you won’t have a large immune response when you’re exposed to Ad26 again. That could lower vaccine efficiency, but it could mean that a boosted dose is possible. They are doing trials to see if a 2 dose regimen is better. We should have a better answer after those trials.
Is That Why This is a One Dose Only Shot?
Partially. The real reason is that is the way the trial was designed. They could have just as easily designed the trial with a booster dose. However, one shot is a marketing advantage of the J&J vaccine, and a real world advantage to rural populations, the homeless, and other patients you have a hard time getting into your office for even one shot. If one shot can give pretty good and long lasting immunity, that’s great.
The data seems to say it’s “good” immunity. The vaccine is really efficient at preventing serious disease. It looks like it prevents some transmission too, however, like most vaccines it doesn’t appear to be sterilizing (see the discussion on the mRNA vaccine FAQ). We’ll see how long lasting the protection is and how good it is at protecting against variants as time goes on.
*I haven’t thoroughly reviewed the FDA data yet, I’ll update this in a few days when I have had a chance to do it with more info.