mRNA vaccines work differently than traditional vaccines. They tell the body how to make a protein that produces immunity against specific microbes. In contrast, traditional vaccines use weakened or dead microbes, or pieces of them, to stimulate immunity.

Both types of vaccines have advantages. mRNA vaccines have a shorter manufacturing time, but some traditional vaccines can provide lifelong immunity against an infection.

This article discusses mRNA vaccines vs. traditional vaccines, including how both types work and the advantages and disadvantages of each. It also examines the safety and effectiveness of both types, as well as the side effects.

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mRNA vaccines are a relatively new type of vaccine. They contain genetic material, or mRNA, that tells the body how to make a protein. This protein causes an immune response, which teaches the body how to protect itself from a specific virus.

For example, the virus that causes COVID-19, SARS-CoV-2, has spike proteins on its surface. The COVID-19 vaccine causes the body to make this protein, and the presence of the protein causes the body to behave as though it has a SARS-CoV-2 infection, even though it does not.

In response, the immune system mounts a response to SARS-CoV-2, which includes releasing antibodies to fight the virus. As a result, if a person is exposed to SARS-CoV-2 after vaccination, their immune system will already know how to recognize and attack the virus before it can cause severe illness.

Because mRNA vaccines do not contain viruses or any other microbes, they cannot give a person an infection. They also do not change a person’s DNA.

Traditional vaccines work in a different way. The exact mechanism depends on the type of vaccine.

Live vaccines

Live vaccines use a weakened form of a microbe that causes an infection. The immune system responds to the weakened microbes, producing strong and lasting protection against future infections.

Many live vaccines provide lifelong protection from a certain infection. However, because they contain a small amount of live virus, they may not be suitable for people with weakened immune systems.

Live vaccines can provide lifelong immunity against:

Inactivated vaccines

Inactivated vaccines use dead microbes rather than live ones. They do not offer as much protection as live microbes do, so booster shots may be necessary to produce ongoing immunity.

This type of vaccine can protect against:

Subunit, recombinant, polysaccharide, and conjugate vaccines

These vaccine types use only part of a microbe, such as a protein, sugar, or casing that surrounds the microbe. They provide a strong immune response, but booster shots may be necessary. They are safe for most people, including those with weakened immunity.

These vaccines can protect against:

In terms of the immune response they produce, live vaccines provide the strongest and most lasting protection. However, because they contain a live virus, they also have some risks.

For example, doctors do not recommend live viral vaccines during pregnancy because of the risk of viral transmission to the fetus. They also do not recommend these vaccines for people with weakened immunity.

mRNA vaccines may be safer because they do not contain any whole microbes, alive or dead, and therefore cannot transmit any infection.

Both mRNA and traditional vaccines can be highly effective. For example, the COVID-19 vaccine is very effective at preventing severe illness.

A person who receives two or three doses of a COVID-19 vaccine has a 90% lower risk of needing mechanical ventilation or dying from the infection.

Similarly, the smallpox vaccine is 95% effective. Two doses of inactivated polio vaccine are 90% effective, while three doses are even more effective, at 99–100%.

However, the protection that traditional vaccines can offer varies significantly. For example, the flu vaccine reduces the risk of severe flu by 40–60%. This is because several different viruses can cause the flu, and these viruses mutate and change regularly. Therefore, people need to get new flu shots every year.

Despite this variability, doctors still recommend getting vaccines such as the annual flu shot because they can save lives.

Both mRNA and traditional vaccines have advantages and disadvantages. The table below summarizes some of the key differences:

mRNA vaccinesTraditional vaccines
Manufacturing and developmentfasterslower — can take years
Effectiveness and safetyeffective and safe for the vast majority of peoplecan be highly effective but are not safe for everyone
Shelf lifeup to 6 monthsvaries by vaccine but may be 1–3 years
Length of immunitycan require several booster shots over time to maintain immunityvaries by vaccine — may offer lifelong immunity or require booster shots

mRNA vaccines have very few risks. They do not contain any live microbes, unlike some traditional vaccines, and all vaccines must pass rigorous safety testing before the general public can receive them.

However, like other vaccine types, mRNA vaccines can cause side effects in the days after a person receives them. These side effects tend to be mild and temporary.

After a person receives the shot, their arm may feel achy, painful, or swollen. People may also experience flu-like symptoms. These are more common after the second dose and can include:

The COVID-19 vaccine has a small risk of pericarditis and myocarditis, which is most likely to occur in male adolescents and young adults. Pericarditis is inflammation of the outer lining of the heart, and myocarditis is inflammation of the heart muscle.

However, these complications are rare, and people who develop them typically feel better quickly with rest and medication.

Another rare complication is anaphylaxis, a severe allergic reaction. If a person has never had a COVID-19 vaccine before, a medical professional may ask them to stay for 15 minutes after receiving their dose. This allows medical professionals to monitor for symptoms.

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

  • hives
  • swelling of the face or mouth
  • wheezing
  • fast, shallow breathing
  • a fast heart rate
  • clammy skin
  • anxiety or confusion
  • dizziness
  • vomiting
  • blue or white lips
  • fainting or loss of consciousness

If someone has these symptoms:

  1. Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
  2. Dial 911 or the number of the nearest emergency department.
  3. Lay the person down from a standing position. If they have vomited, turn them onto their side.
  4. Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5–15 minutes, or they come back, use a second pen if the person has one.

mRNA vaccines are a newer type of vaccines that work by telling the body to make a protein. This protein triggers an immune response, providing protection against future infections. In contrast, traditional vaccines contain weakened or dead viruses or parts of viruses, which also trigger an immune response.

Both mRNA vaccines and traditional vaccines have advantages and disadvantages. mRNA vaccines have a shorter manufacturing time and cannot transmit a viral infection, unlike live vaccines. However, traditional vaccines have a longer shelf life, and some offer lifelong immunity against infections.

Both types can cause side effects but are safe and effective for most people. The benefits of vaccination often outweigh the risks.

However, there are some exceptions. A person who is pregnant, has a weakened immune system, or has had allergic reactions to vaccinations in the past should consult a doctor before getting a vaccine.