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COVID-19 Vaccines

Adapted with generous permission from Peg (Margaret) Burnette, Associate Professor, University Library & Carle Illinois College of Medicine, Medical and Biomedicine Librarian.






Ethan Annis

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Ethan Annis
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How do vaccines work?

Simply put, a vaccine trains the immune system to recognize viruses, bacteria, and other germs, or pathogens, so the body can react. The human body produces special proteins called antibodies to fight germs like the virus that causes COVID-19. Vaccines introduce weakened or killed parts of pathogens, or elements that mimic their structure, into the body.

COVID-19 vaccines cause your body to safely develop antibodies that recognize and fight the coronavirus that causes the disease, greatly reducing the risk of a full-scale infection.

SOURCE: HHS Combat Covid

HHS - How do Vaccines Work?

How do mRNA Covid-19 vaccines (such as the Pfizer/BioNTech and Moderna Covid-19 vaccines) work?

Two messenger RNA (mRNA) vaccines are currently available in the United States, one developed by Pfizer/BioNTech (BNT162b2) and the other by Moderna (mRNA-1273). In these vaccines, the mRNA carries instructions to make the SARS-CoV-2 “spike” protein — the prickly projections on the surface of the virus, which is structured like those rubber balls that dogs love to chase or like the quills of a porcupine.

Once the vaccine is injected, the mRNA is taken up by the macrophages near the injection site and instructs those cells to make the spike protein. The spike protein then appears on the surface of the macrophages, inducing an immune response that mimics the way we fight off infections and protects us from natural infection with SARS-CoV-2. Enzymes in the body then degrade and dispose the mRNA. No live virus is involved, and no genetic material enters the nucleus of the cells.

Although these are the first mRNA vaccines to be broadly tested and used in clinical practice, scientists have been working on mRNA vaccines for years. And despite this wonderful parody piece. opens in new tab saying that the technology is “obvious,” in fact the breakthrough insight that put the mRNA inside a lipid coating to prevent it from degrading is quite brilliant — and yes, this may be the first time the New England Journal of Medicine has referenced a piece in The Onion. (Last reviewed/updated 23 Mar 2021)

SOURCE: NEJM Covid-19 Vaccine - FAQs


How do adenovirus Covid-19 vaccines (such as the Johnson & Johnson vaccine) work?

The J&J vaccine is a recombinant replication-incompetent human adenovirus serotype 26 vector encoding a full-length, stabilized SARS-CoV-2 spike protein antigen. That’s quite a lot to digest, so let’s unpack it in words that are more easily understandable by us mere mortals:

  • “recombinant” — genetically engineered in a lab. Yes, I know it can mean more than this, but that’s the gist.
  • “replication-incompetent” — can’t reproduce in humans. No risk of viral dissemination.
  • “adenovirus serotype 26” — there are many adenovirus serotypes in the community. This one is uncommon, which is important because preexisting immunity to an adenovirus might diminish our response to the vaccine. The name of the J&J vaccine refers to this serotype (Ad26) and the antigen it carries — Ad26.COV2.S.
  • “vector encoding” — the virus acts as a transporter (vector) of the gene — the DNA — that makes (encodes) the antigen, which is a …
  • “full-length, stabilized SARS-CoV-2 spike protein antigen” — the researchers have taken the genetic machinery, or DNA, from SARS-CoV-2 that makes the whole spike antigen, and made it stable enough to be carried within the adenovirus.

When the vaccine is injected, the adenovirus cannot replicate, but its genetic material can enter the host cell’s nucleus and be converted to messenger RNA. The mRNA then creates spike protein antigens from SARS-CoV-2, which elicit a host response similar to natural infection with the virus that causes Covid-19. Both antibody and cellular immunity is stimulated.

Note that there are other adenovirus vector vaccines in use globally that carry the SARS-CoV-2 spike protein DNA. Neither is yet available here in the United States, and both use two doses as their vaccine strategy. The Oxford/AstraZeneca vaccine uses a chimpanzee adenovirus modified so it does not replicate in humans. The Sputnik V vaccine starts with the same Ad26 adenovirus as the J&J vaccine, but then switches to adenovirus serotype 5 for the second dose. This switch theoretically improves the boosting effect of this vaccine, as it reduces the chance that acquired immunity to Ad26 will diminish the immune response. (Last reviewed/updated 29 Mar 2021)

SOURCE: NEJM Covid-19 Vaccine - FAQs


It can be difficult to know which sources of information you can trust. Learn more about finding credible vaccine information.


Beware of Fraudulent Coronovirus Tests, Vaccines, and Treatments