The Johnson & Johnson vaccine is the first one-shot regimen — and is a typical vaccine.

It contains cold viruses that have been genetically tweaked so that they cannot make copies of themselves. When those harmless cold viruses infect cells, they deliver the genetic blueprint of the coronavirus spike protein, and the cell learns to build the spike. The immune system learns to recognize and block the real virus.

In contrast, the Pfizer-BioNTech and Moderna shots are the first vaccines using messenger RNA technology approved for human use by the Food and Drug Administration.

The approach is different from that of more traditional vaccines, which often use a weakened or dead version of a virus, or a laboratory-generated protein. It uses a synthesized scrap of genetic information that is wrapped in a protective fat layer to keep it from disintegrating. When it goes into cells in the muscle of the upper arm, it contains molecular instructions that tell your cells to create a protein that triggers an immune response to the spike protein on the surface of the coronavirus. This means your immune system will be prepared to eliminate the pathogen if it tries to invade.

All of the vaccines passed rigorous safety reviews by the FDA.

The agency authorized the Pfizer-BioNTech vaccine for people ages 16 and over after reviewing data from 44,000 participants in a randomized clinical trial. A 53-page analysis by the agency found that some people who received injections had unpleasant but tolerable side effects, including fatigue, headaches, muscle pain, joint pain, chills and fever. Reviewers said the two months of follow-up on 38,000 of those participants provide evidence of “a favorable safety profile, with no specific safety concerns identified that would preclude issuance of an [emergency authorization].”

The FDA cleared the Moderna vaccine for people ages 18 and over, based on data from a clinical trial with 30,000 participants. The agency found side effects were similar to those with the Pfizer-BioNTech shot.

The Johnson & Johnson vaccine was authorized for people ages 18 and over, based on data from a trial with 44,000 participants. Side effects from the vaccine were less common than those for Moderna and Pfizer-BioNTech and included pain at the injection site, fatigue and headaches.


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