How Vaccines Work

Vaccines stimulate our immune systems to recognize foreign invaders and attack them. White blood cells (macrophages, B‑lymphocytes, T‑lymphocytes) help to fight the possible infection. As antigens are engulfed and presented by macrophages to antigen presenting cells, this leads to antibody production by the B‑lymphocytes. In this instance, both the antigen and the subsequently produced antibody are major players in an individual’s defense. Vaccines harness this natural function and work by creating a “memory” so that if infected by the same organism, it is recognized as foreign and destroyed.

There are three main types of COVID‑19 vaccines that are undergoing large-scale (Phase 3) clinical trials in the United States and globally. Further, most COVID‑19 vaccines require more than one vaccination injection and effective dosages and transportation variables may change.

mRNA vaccines are being utilized for public health applications for the first time against COVID‑19. They contain messenger RNA (mRNA) from the coronavirus (that causes COVID‑19) that gives our cells instructions for how to make a harmless protein that is unique to the virus and is highly conserved amongst coronaviruses. This messenger RNA does not enter the host cell nucleus but is transported to the endoplasmic reticulum (ER), the protein creation factory of the cell.⁶⁷ After host cells make copies of the protein, they destroy the mRNA from the vaccine. Our bodies recognize that the protein is non-self and build T-lymphocytes and B-lymphocytes that will remember how to fight the virus that causes COVID‑19 if we are infected in the future.⁶⁷ Examples of mRNA vaccines are the Moderna and Pfizer vaccines.

Protein subunit vaccines include harmless pieces (proteins) of the virus that cause COVID‑19 instead of the entire virus, which could cause disease. A protein subunit vaccine from the company Novavax (Gaithersburg, MD) is currently under investigation in the United States.

Vector vaccines use a weakened version of a different virus than the one that causes COVID‑19 and its framework for replication (e.g. the virus that can cause the common cold), which has genetic material from the virus that causes COVID‑19 inserted in it (this is called a viral vector).⁶⁷ Once the viral vector is inside our cells, the genetic material gives cells instructions to make a protein that is unique to the virus that causes COVID‑19. These vaccines prompt the body to build T-lymphocytes and B-lymphocytes that will recall how to combat that virus if one is infected in the future. Both the Johnson & Johnson vaccine and the AstraZeneca vaccine are vector vaccines.

As of April 2021, large-scale (Phase 3 and Phase 4) clinical trials are in progress or being planned for five COVID‑19 vaccines in the United States: AstraZeneca’s COVID‑19 vaccine; Janssen’s COVID‑19 vaccine; Moderna’s COVID‑19 vaccine; Novavax’s COVID‑19 vaccine; and Pfizer’s COVID‑19 vaccine.⁶⁸