All the Differences Between the Covid Vaccines, Explained

All offer protection, but how they do it varies.

When the Moderna and Pfizer vaccines rolled out with mRNA technology, everyone wondered exactly what that meant. Now, other vaccines are on the horizon in the US—some are already authorized for use in other countries—with different and sometimes more traditional technologies behind them.

The bottom line is this: Each type of Covid-19 vaccine that’s been developed or is being developed—mRNA, vector, and protein subunit—has its own way of doing things. But they all have one thing in common. “Each vaccine works by stimulating an antibody-mediated immune response to attack the virus that causes COVID-19,” says Jay W. Lee, MD, MPH, a practicing family physician in Orange County, California.

All of the vaccines get you to the same place—they prime your immune system to protect you from Covid. But exactly how does each vaccination work? Here’s a snapshot:

mRNA vaccine
Vaccines that use this: Pfizer, Moderna

How it works: mRNA or messenger RNA may be labeled as the newest vaccine in town, which is true, but as we have previously reported, the technology surrounding it is not entirely unknown, as mRNA research has been in the works since the 90s. This type of vaccine injects instructions, via a piece of genetic code, that tell your body how to make a certain protein essential to blocking the virus. “The mRNA vaccines instruct our cells to recognize COVID-19 and produce a harmless “spike” protein,” explains Dr. Lee. These proteins train your immune system to recognize the virus and make antibodies to attack that virus if it arrives in your body. The instructions quickly vanish, but your immune system stays fortified.

Vector vaccine
Vaccines that use this: Johnson & Johnson, AstraZeneca (not yet available in the U.S.)

How it works: Vector vaccines are made from a modified version of a live virus, says Dr. Lee. Those harmless viruses—in this case, an adenovirus, which is a version of the common cold—are sent into your body containing an instruction manual that tells your cells to make a spike protein; a harmless piece of the SARS-CoV-2 virus (that’s the one that causes Covid-19). Vector vaccines will not give you Covid-19. Your body starts to make antibodies to this so that if the real spike protein comes around on the Covid-19-causing coronavirus, the antibodies will attack it and ultimately help defend your body. If you’ve had an MMR (measles, mumps, and rubella) or chicken pox vaccine, these work in a similar manner.

Protein Subunit vaccine
Vaccines that use this: Novavax (still in clinical trials)

How it works: This is what’s currently used in the Hepatitis V and one of the shingles vaccines (Shingrix). Protein subunit vaccines are a little bit like vector vaccines, but instead of using a different virus to send in the genetic message, these “contain harmless pieces of the virus that causes Covid-19 but not the entire virus,” says Dr. Lee. Once these parts or subunits, which can be things like the germ’s protein, sugar, or a casing around the germ known as a capsid, get into the body, our immune system recognizes that they are foreign, promotes the making of antibodies, which in turn fights the virus.

What kind of vaccine is the flu vaccine?
Since we are in the midst of flu season (it peaks this month, but will last until May), you may also be wondering where the flu vaccine falls in all this. The shot version (there is also a nasal spray) uses an inactivated virus or single protein from the flu virus, and essentially does the same thing as the Covid-19 vaccines mentioned above: It introduces your body to parts of different flu viruses. This puts your immune system on the defensive to help rid your body of this foreign substance. Antibodies are made, and then offer protection down the line. The tricky thing about the flu vaccine’s effectiveness is that it is going to vary from season to season because there are different types or the virus that circulate each year. So medical experts never know exactly which will hit us and often are making highly-educated guesstimations.

The most important takeaway from all of this? Protection against the Covid-19 is key. All of these types of vaccines are just different routes to get your body to protect you.