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How Vaccines Work

The first human vaccine was developed in 1796, which ultimately led to the elimination of smallpox — a painful, disfiguring and often deadly disease. Now, 225 years later, there are protective shots for more than three dozen diseases, each one created to reduce human suffering.

But how do vaccines work? The simplest explanation is that vaccines teach your immune system to fight against certain germs and viruses which cause diseases such as bubonic plague, rabies, Ebola and measles, to name a few. When parts of a virus or germ are inserted into your body, your immune system reacts by producing antibodies to fight the disease. Often, these antibodies continue to protect you from future exposures to the disease.

Scientists have developed several types of vaccines that work in different ways to prevent or lessen disease, including:

  • Inactivated vaccines. These use the killed version of the germ that causes a disease. These types of vaccines have been developed to protect against hepatitis A, the flu, polio and rabies.
  • Live vaccines. These use a weakened form of the germ that causes a disease. Just one or two doses of most live vaccines can give lifelong protection against such diseases as measles, mumps, rubella, chickenpox and others.
  • Messenger RNA vaccines. These vaccines, also called mRNA vaccines, have been studied for decades, but have gained notoriety as the technology behind some of the COVID-19 vaccines now being used. These vaccines work by making proteins that trigger an immune response. Because they do not contain live virus, there is no risk of causing the disease in the person getting vaccinated.

No matter how they are made, vaccines are overwhelmingly safe. According to the U.S. Department of Health & Human Services, most people will have only mild, short-term side effects after receiving a shot, and just one to two people out of a million will have a serious allergic or other reaction to a vaccine.

The History of mRNA Vaccines

Today’s success with mRNA vaccines against COVID-19 comes from the decades of research that came before it.

1980s: Love those lipids Researchers study the nature of
lipids, which lays the groundwork for
using lipid nanoparticles in mRNA
vaccines many decades later.
1990s: Failing forward Could synthetic forms of RNA be
used in medicine? The potential
seems endless, but so do the
challenges. Failed experiments still
build knowledge.
2000s: And we’re off! In 2005, scientists figure out how
to make synthetic RNA safe for
injection into cells. Research in the
field accelerates.
2010s: Smarts and spikes After outbreaks of other
coronaviruses in 2003 (SARS) and
2012 (MERS), scientists study how
the “spike protein” works and how it
could be used in vaccines.
2020: Success! Vaccines tested, approved and

 Source: Canadian Institutes of Health Research.