Chickenpox is a viral infection caused by the varicella zoster virus (a herpes virus). It causes symptoms like blisters, rashes, fever, and more. It is transmitted easily through contact with other people who have an active chickenpox infection. The infection lasts between five and 10 days and is normally mild. However, some people with chickenpox experience serious health issues.

A chickenpox vaccine became available in the United States in 1995, preventing millions of infections and many hospitalizations and deaths. This article discusses the chickenpox vaccine, its effectiveness, and potential risks and side effects.

What Is the Chickenpox Vaccine?

The chickenpox (varicella) vaccine is an immunization that most people in the United States receive when they are young children.

There are several types of vaccines. The chickenpox vaccine is a live-attenuated vaccine.

Live-attenuated vaccines contain a weakened version of the germ the vaccine is being used to prevent. The weakened version of the germ in the vaccine will produce an immune response that can result in lifelong immunity in just one or two doses.

However, this type of vaccine may not be appropriate for every person. For example, those who have had an organ transplant, are immunocompromised, or have certain chronic health issues may need to speak with a healthcare provider before considering this type of vaccine.

There are two chickenpox vaccines approved for use in the United States:

• ProQuad: This version is a combination vaccine. It contains the measles, mumps, rubella, and chickenpox vaccines. It is approved for use in children between the ages of 12 months and 12 years.
• Varivax: This is a chickenpox–only vaccine that is approved for use in adults, adolescents, and children who are 12 months and older.

Both chickenpox vaccines are administered in two doses.

When used to prevent chickenpox (before there is a concern of possible exposure), the timing of the doses depends on at what age you received the first dose. Babies who get the first dose of the vaccine when they are between 12 months old and 15 months old will get a second shot between the ages of 4 and 6 years old.

Who Should Get the Chickenpox Vaccine?

The chickenpox vaccine is a routine childhood vaccination recommended for all children. The Advisory Committee on Immunization Practices (ACIP) recommends that all healthy people get the vaccine. The only exception would be for people who have evidence of immunity, which can include:

• Having lab results confirming immunity or infection
• A diagnosis of chickenpox or herpes zoster from a healthcare provider

People born before the year 1980 are considered to have immunity, with the exception of those who are immunocompromised, pregnant, or work in a healthcare setting.

One version of the vaccine may be given if someone suspects they may have been exposed to chickenpox as postexposure prophylaxis (after exposure to the virus) to reduce the risk of infection. This is recommended for unvaccinated, healthy people 12 months or older who do not have evidence of immunity to prevent the disease. For maximum effectiveness, it must be administered within five days after exposure.

Chickenpox Vaccine Mandate

There is no federal law requiring the chickenpox vaccine. However, laws in all 50 states and Washington, D.C. require children attending public school or childcare to be immunized against chickenpox. The ACIP recommends that:

• Children who are preschool age (between 12 months and 3 years old) have one dose of the vaccine
• All other school-age children through adults have two doses

Exemptions to the vaccine are handled on a state-by-state basis as well.

There are other situations in which the chickenpox vaccine may be required in the interest of public health. For instance, immigrants to the United States are required to receive the chickenpox vaccine in addition to a number of other immunizations, some of which are explicitly outlined by the Immigration Nationality Act.

Who Should Not Get the Chickenpox Vaccine?

People should not get the chickenpox vaccine if they have ever had a life-threatening allergic reaction to a previous dose of the chickenpox vaccine or any ingredient of the vaccine, including gelatin or the antibiotic neomycin.

Additionally, the ACIP recommends that certain groups of people wait to get the chickenpox vaccine or speak with their healthcare provider about getting it.

It's recommended to wait to get the vaccine if you are:

• Currently sick with moderate to severe illness
• Pregnant

Talk with your healthcare provider if you are/have:

• Living with human immunodeficiency virus (HIV)
• Undergoing treatment that affects your immune system
• Living with cancer or are undergoing cancer treatment
• Had a blood transfusion or treated with other blood products
• First-degree relatives (parents, children, siblings) who have an inherited immune disorder
  

Effectiveness

Research has found that the vaccine is highly effective and prevention of chickenpox starts with the first dose.

After the first dose, the vaccine is about 80% effective at preventing any chickenpox infection and 95%–98% effective at preventing a moderate or severe infection.

With two doses, the effectiveness increases to prevent 92%–93% of any chickenpox infection.

Risk and Side Effects

Side effects of the vaccine may include:

• Soreness at the injection site
• Redness at the injection site
• Rash at the injection site
• Fever

Anyone who gets a rash after being vaccinated may be able to pass the virus to another person. In that case, they are advised to stay away from infants and people who have compromised immune systems.

It's also possible that people may develop shingles (herpes zoster), which causes a painful rash, years after getting the vaccine. However, shingles occurs less often after getting the chickenpox vaccine than after having a chickenpox infection.

Because the chickenpox vaccine contains a live, weakened virus, people who have compromised immune systems may develop a severe and potentially life-threatening infection after getting the vaccine. The vaccine is not recommended for people who have a compromised immune system.

Summary

The varicella vaccine is highly effective at preventing chickenpox. It's administered in two doses and is required for children who will be entering public school in the United States. The vaccine is a routine childhood vaccination that is recommended for all healthy people who do not already have evidence of immunity to the varicella virus.

However, because the vaccine contains a live, weakened version of the varicella virus, it may not be safe for some people. Your healthcare provider can help determine if the vaccine is safe for you.

A Word From Verywell

Vaccines like the varicella vaccine are effective public health tools for preventing certain diseases in individuals and communities. Getting vaccinated, if you can, can help keep other people in your family, workplace, place of worship, or community who can't be vaccinated stay healthy. If you didn't receive the vaccine as a child, speak with your healthcare provider to discuss vaccination as an adult.