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Vaccines: How They Were Made and How They Work

COVID-19 vaccines are marvels of modern medicine.

The science behind them is the result of decades of research. That’s why they could be developed in less than a year.


The U.S. vaccine safety system ensures that all vaccines are as safe as possible. Any vaccines with Emergency Use Authorization (EUA) have been tested according to the federal Food & Drug Administration’s (FDA) rigorous standards.

Most of the time, vaccine developers run one test at a time.

Because of the historic nature of the COVID-19 pandemic, researchers ran many of these tests at the same time. This sped up the testing process without compromising safety. It’s like the difference between a four-person relay race of 400 yards and a 100-yard dash with four runners. The relay takes about four times as long for the same result – four people each running 100 yards.

Two Dose Vaccines

The vaccines made by Pfizer-BioNTech and Moderna use messenger RNA (mRNA), a genetic material containing instructions for making proteins.

The mRNA is coated with a fat nanoparticle (think of a fatty overcoat) to protect it. Inside the body, the outer coat is removed, and the mRNA enters the immune system, teaching it to create only the “spike” protein found on the surface of the virus. (those are the spiky things you see in pictures of viruses).

The body recognizes the spike protein as an invader and produces antibodies against it. Later, if the antibodies encounter the actual virus, they recognize those spike proteins and destroy it.

Think of the spike protein like a key trying to unlock our cells. The antibodies from the vaccine block the keyhole, preventing the virus from intruding. The mRNA strand never enters the cell’s nucleus or affects genetic material. The vaccine can’t alter your DNA or give you COVID-19.

Pfizer-BioNTech vaccine

  • Two doses, 21 days apart; peak immunity two weeks after second dose
  • 95% effective at preventing symptomatic COVID-19
  • For children and adults 6 months and older

Moderna vaccine

  • Two doses, 28 days apart, peak immunity two weeks after second dose
  • 94.1% effective at preventing symptomatic COVID-19
  • For children and adults 6 months and older

Adenovirus vaccines
Some vaccines, like the Janssen Biotech (Johnson & Johnson) vaccine, which the FDA approved this week for emergency use against COVID-19, use a common cold virus called an adenovirus.

In the adenovirus vaccine, a small amount of genetic material from the spike protein attaches to the cold virus. Think of it as the adenovirus wearing a backpack containing the spike protein’s genetic material. In the body, the adenovirus enters cells and unpacks the backpack, tricking them into producing the spike protein. This, in turn, triggers the immune system to produce antibodies that protect against the real virus.

Adenovirus vaccines also can’t alter your DNA or give you a cold or COVID-19.

Janssen (Johnson & Johnson) vaccine:

  • One dose; peak immunity two weeks after shot
  • 85% effective at preventing severe COVID-19
  • For people age 18 and older


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