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Chicken pox And Varicella Vaccine: What You Need To Know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Feb 2, 2022.

What Is Chickenpox?

Chickenpox is a highly contagious viral disease that can be easily caught by direct or indirect contact with chickenpox blisters, or by breathing in infectious droplets released into the air when an infected person coughs or sneezes. It is caused by the varicella-zoster virus (VZV), the same virus that causes Shingles. VZV is one of eight herpes viruses known to infect humans.

Symptoms appear from 10 to 21 days after a nonimmune person has been exposed to droplets of mucus or blister-fluid containing the chickenpox virus.

What Are The Symptoms of Chickenpox?

Chickenpox symptoms can vary between adults and children. The mildest form of chickenpox usually occurs in people who develop symptoms despite being vaccinated against the disease.

Some people, usually adults (although children can be affected as well), develop a prodrome one to two days before the characteristic chickenpox rash occurs. This prodrome usually consists of a fever, headache, and abdominal pain. People with this prodrome will usually comment, "I feel like I'm coming down with something".

The rash begins as small areas of skin discoloration which rapidly progress to small, raised, red spots that fill with a clear fluid. These fluid-filled spots are called vesicles and they can be intensely itchy for the first three to four days until the vesicles crust over and form scabs. The rash usually appears first on the head, chest, and back before spreading to the arms and legs.

Blisters may also form inside the mouth, nose, throat, vagina, or on the penis. People also generally feel unwell and have a fever for the first few days of chicken pox. The blisters usually crust over and disappear within about 10-14 days.

Why Did I Get Chickenpox Even Though I've Been Vaccinated?

Previous vaccination with a varicella vaccine does not always guarantee that a person will not develop chickenpox symptoms. However, if they do, these symptoms are usually much milder than in an unvaccinated person.

The effectiveness of vaccination depends upon how many doses of the vaccine have been given, and how strong the person's immune system is. According to the Centers for Disease Control and Prevention (CDC), one dose of varicella vaccine is 82% effective at preventing any form of chickenpox, and 100% effective at preventing the severe form of the disease. Two doses of varicella vaccine increase the effectiveness against any form of varicella to 98%. Effectiveness rates may be lower in people with other health conditions such as HIV or who are immunocompromised (for example, taking medications that suppress the immune system).

Chickenpox that occurs in a person who has been previously been vaccinated against the disease is called “breakthrough varicella”, and it is usually mild. People with breakthrough varicella typically don’t have a fever, or only have a low-grade fever, and develop fewer than 50 skin lesions. The rash tends to be milder and lacks the vesicles typically seen in unvaccinated people who develop the disease. People with breakthrough varicella also tend to recover quicker than unvaccinated people.

Vaccination is generally long-lasting although experts aren't sure exactly how long it lasts for. Some studies have shown antibodies against varicella are still present 10 to 20 years after vaccination.

I Got Chickenpox When I Was A Kid. Can I Get It Again?

Most people only get chickenpox once. That is because one natural infection usually confers immunity for life.

Getting chickenpox twice is very rare but is more common in people whose immune systems have been compromised in some way (which can happen if you develop cancer or take medications such as prednisone).

It is more likely that people will develop shingles from reactivation of the varicella-zoster virus than a second attack of chickenpox. This is because once chickenpox has resolved, the virus does not leave the body. Instead, it remains dormant (sleeping) in the nerve cells close to the spinal cord.

Nobody knows exactly how the virus remains dormant, or what triggers it to reactivate again. But symptoms of shingles are vastly different from those of chickenpox and include a painful, red, blistering rash that typically affects one side of the face or torso. For more about shingles, see our slideshow: Shingles: Settling The Score.

What Vaccinations Are Available Against Chickenpox?

There are two vaccines in the U.S that protect against chickenpox:

  • Varivax - which only contains the varicella virus (chickenpox) vaccine and is approved for children aged 12 months or older
  • Proquad (also called MMRV), a combination vaccine which contains the varicella virus vaccine as well as vaccines against measles, mumps, and rubella. It is approved for children aged 12 months to 12 years.

The CDC recommends that children should receive two doses of a varicella vaccine. The first should be given to infants aged between 12 and 15 months, and the second to children aged between four and six years. The ACIP (Advisory Committee on Immunization Practices) recommend Varivax be administered at the same time as MMRII in children aged between 12 and 15 months (unless a parent/caregiver requests Proquad as the first dose), then Proquad be given as the second dose to children aged between 4 and 6 years. There should be a minimum of 3 months between doses.

Any adult or adolescent aged 13 years or older who does not have evidence of immunity to chickenpox should also receive two doses of Varivax. The second dose should be given 4 to 8 weeks apart. If it has been longer than 8 weeks since the first dose, the second dose may be given without restarting the schedule. MMRV should not be used in children older than 12.

Healthcare personnel, teachers, child care workers, college students, inmates, and military personnel are all recommended to be vaccinated against varicella. However, varicella vaccine should not be given to pregnant women and people who are severely immunocompromised. In people with HIV with no evidence of immunity, a 2-dose series should be considered; however, varicella vaccine is contraindicated in people with HIV with a CD4 count < 200 cells/microliters. For more details about immunization, see here for children and here for adults.

The chickenpox vaccine has been available in the U.S. since 1995. Prior to widespread use of the vaccination, nearly 11,000 people were hospitalized each year with chickenpox and about 100 adults and children died.

Side effects of vaccination are generally mild and short-lived and may include pain and redness at the site of the shot. One out of every 25 children who get the vaccine experience a fever and a mild rash. There is a slightly higher risk of febrile seizures developing in children who receive the MMRV vaccine instead of separate MMR and varicella vaccines, although this is rare. Talk to your doctor if you have any questions.

How Do You Treat Chickenpox?

In people who have developed chickenpox, calamine lotion, colloidal oatmeal baths, or antihistamines may help relieve some of the itching. It is important for the person not to scratch because this can spread germs from the skin and cause an infection, which can lead to serious complications in some people.

Acetaminophen (Tylenol) may be used to make a person with chickenpox feel more comfortable. Avoid using aspirin or products that contain aspirin in children under the age of 18 with chickenpox. Aspirin use in people with viral illnesses such as chickenpox has been associated with a higher risk of Reye’s syndrome, a condition that can cause liver and brain damage and even death.

Some people, such as those older than 12 or taking certain medications such as salicylates or prednisone, are at a higher risk for severe chickenpox infection and may be given an antiviral treatment such as acyclovir, valacyclovir, or famciclovir. This type of medication works best if given within 24 hours of the onset of the rash.

People with chickenpox should stay away from school or work for about two weeks or until the last of the blisters have crusted over. During that time, if possible, they should avoid contact with people who are immunosuppressed, pregnant, or not immune to the virus.

When Should a Person With Chickenpox See a Doctor?

Always call a doctor if a person in your household younger than one year or over the age of 12 develops chickenpox, or if chickenpox develops in a family member or friend with a weakened immune system or who is pregnant.

Also, seek immediate medical attention if a person with chickenpox experiences the following:

  • A fever lasting longer than 4 days
  • A fever greater than 102°F (38.9°C)
  • Signs of a bacterial infection (includes warmth and pain near the rash, or the presence of pus)
  • Becomes difficult to rouse or acts confused
  • A stiff neck, has difficulty breathing, or vomits frequently
  • A severe cough or complains of severe abdominal pain
  • A rash that is bleeding or bruises develop near the rash.

If you have been exposed to a person with chickenpox, and you are unvaccinated or have never had chickenpox yourself, then it is recommended you get vaccinated as soon as possible (within 3 to 5 days following exposure). There is some evidence that this may prevent illness or reduce the seriousness of the disease.

Finished: Chicken pox And Varicella Vaccine - What You Need To Know

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