What Is an Inactivated Vaccine?

An inactivated vaccine is one that uses a killed virus or bacteria to stimulate the immune system to protect the body against infection. Because the bacteria or virus is dead, it cannot replicate or cause disease.

While inactivated vaccines have the same aims as live vaccines—namely to generate antibodies that fight diseases—they tend to induce a less robust response and often need multiple doses and/or booster shots to achieve the same level of protection.

Woman administering a vaccine
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History

Inactivated vaccines were first developed at the end of the 19th century. While the practice of variolation (inoculating an uninfected person with pus from an infected person) was commonly used during the 18th century to prevent bacterial infections like smallpox, the practice was also used for diseases like typhoid, plague, and cholera.

Scientists in the 19th century learned that by isolating the disease-causing pathogen and killing it, the body would still recognize it as harmful when it was introduced into the body and trigger a disease-specific response. This lead to the development of the first inactivated vaccines in the 1880s and the first general-use cholera vaccine in 1896.

Over the generations, scientists have used different methods to kill pathogens being prepared for inactivated vaccines, including heat, chemicals, and radiation.

By the 20th century, chemical inactivation was successfully applied to viruses, in some cases involving the whole pathogen and, in others, only part of the pathogen. It is the latter discovery that led to the development of the subunit vaccine.

Types of Inactivated Vaccines

There are 85 single and combination vaccines approved for use by the U.S. Food and Drug Administration (FDA). Among these are a small handful of inactivated vaccines, also known as whole-killed vaccines, that protect against the following diseases:

Some inactivated vaccines are no longer available in the United States, including those for cholera and plague.

There is also a live vaccine for influenza that is licensed in the United States called FluMist, as well as a live oral vaccine for polio, which is not.

Advantage and Disadvantages

There are pros and cons to every vaccine. In many cases, there is only one version of a vaccine to choose from, making any comparison moot.

Even so, understanding how inactivated vaccines work can help you understand why vaccine doses differ and why some cost more than others.

Vaccine Durability

Vaccine durability refers to the timeframe that a vaccine is effective. Comparatively speaking, the durability of inactivated vaccines tends to fall short when compared to live vaccines. This is because the immune system can better "recognize" a bacteria or virus that actively replicate even if it doesn't cause disease.

While inactivated vaccines may require up to five doses to achieve the optimal level of protection, live ones generally require one or two. For instance, a live vaccine like the measles, mumps, and rubella (MMR) vaccine only requires two doses but delivers what is effectively lifetime protection.

By contrast, an inactivated vaccine like the one used for rabies may be needed every six months to two years for those at increased risk of exposure, such as veterinarians, animal control and wildlife officers, and those who work in rabies virus research labs.

The same applies to the oral typhoid vaccine, which requires repeated doses every five years for people in endemic regions. (There is also an inactivated typhoid vaccine delivered by injection that requires a repeat dose every two years.)

While subunit vaccines are technically inactivated, they do not involve the whole pathogen (but rather a fragment of a pathogen) and are considered a distinct category of vaccines. Their response tends to be more robust than inactivated vaccines because the fragment used was chosen because of its strong antigenic (immune-stimulating) effect.

Even so, subunit vaccines often need booster shots to maintain immune protection.

Storage and Shipping

Inactivated vaccines have the advantage of being easily stored and shipped. Because the pathogen in the vaccine is dead, the vaccines generally do not require refrigeration and are ideal for parts of the world where resources are limited.

Live vaccines, on the other hand, typically require special shipping and storage requirements. While this is not a huge problem in most of the United States, it does create problems in resource-poor areas. These needs can also increase costs and lead to waste due to shorter shelf life.

Storage and shipping have become major topics of concern with the approval of the Moderna and Pfizer COVID-19 vaccines in 2020, both of which require subzero storage temperatures. This limits their distribution to sites that have the facilities to properly store them, slowing the rate of vaccination.

Vaccine Safety

Inactivated vaccines can be given to most people because there is no chance of the dead virus causing disease. With live vaccines, however, there is a small chance that a virus can revert to its original state and cause illness in some people.

With that said, the only vaccine that is known to have reverted to its pathogenic (disease-causing) form is the live oral polio vaccine, which is no longer used in the United States.

Organ transplant recipients on immunosuppressive drugs, people with HIV, and those undergoing cancer chemotherapy in particular should discuss live vaccines with their doctor. Not all live vaccines need to be avoided, but the benefits and risks need to be weighed before such vaccines are given to these individuals.

A Word From Verywell

Vaccines are among the greatest achievements of medical science. Irrespective of their type, the benefits—in terms of prevention of disease, illness, and death—greatly outweigh the risks.

The avoidance of vaccines not only places you or your child at risk but threatens the resurgence of diseases once thought eliminated. Such is the case with measles, a disease declared eliminated in the United States in 2000 that is making a big comeback due in part to anti-vaccination myths and misconceptions.

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