Prior to the availability of varicella vaccine there were approximately 4 million cases of varicella a year in the U.S. Though usually a mild disease in healthy children, an estimated 150,000 to 200,000 people developed complications, about 11,000 people required hospitalization and 100 people died each year from varicella. Varicella tends to be more severe in infants, adolescents and adults than in young children. The most common complications from varicella include bacterial superinfection of skin lesions, pneumonia, central nervous system involvement, and thrombocytopenia.
Ask the Experts: Varicella (Chickenpox)
The varicella zoster virus (VZV) spreads from person to person by direct contact or through the air by coughing or sneezing. It is highly contagious. It can also be spread through direct contact with fluid from a blister of a person infected with varicella, or from direct contact with a skin lesion from a person with zoster (shingles). People with varicella are infectious 1 to 2 days before skin lesions appear until all lesions have crusted over, usually 4 to 7 days after the appearance of skin lesions.
ACIP recommends administration of varicella zoster immune globulin (VariZIG, Saol Therapeutics) to certain people up to 10 days following exposure to varicella or herpes zoster. People for whom VariZIG is recommended are those without evidence of immunity to varicella who are at high risk of severe disease and complications of varicella illness and are ineligible for varicella vaccination. VariZIG given up to 10 days after an exposure can modify or prevent clinical varicella disease. See the varicella zoster immune globulin section below, and www.cdc.gov/mmwr/pdf/wk/mm6228.pdf, pages 574–6, for more information on this topic.
Patients recommended by ACIP to receive VariZIG include:
- Immunocompromised patients without evidence of immunity
- Newborn infants whose mothers have signs and symptoms of varicella around the time of delivery (i.e., 5 days before to 2 days after)
- Hospitalized premature infants born at 28 weeks (or more) of gestation whose mothers do not have evidence of immunity to varicella
- Hospitalized premature infants born at less than 28 weeks of gestation or who weigh 1,000 grams or less at birth, regardless of their mothers’ evidence of immunity to varicella
- Pregnant people without evidence of immunity
If a susceptible person exposed to varicella or zoster is age 12 months or older, and has no contraindications to varicella vaccination, varicella vaccine can prevent or reduce the severity of infection when administered as post-exposure prophylaxis (PEP) as soon as possible, within 5 days after exposure. There is no evidence that vaccination after infection increases the risk of vaccine-associated adverse reactions. If the patient’s exposure does not result in infection, vaccination can protect against future exposures. See the MMWR for details: www.cdc.gov/mmwr/preview/mmwrhtml/rr5604a1.htm.
The minimum age for varicella vaccine is 12 months. Vaccination is not recommended for infants younger than 12 months of age even as post-exposure prophylaxis. CDC recommends that a healthy infant should receive no specific treatment or vaccination after exposure to VZV. The child can be treated with an appropriate antiviral medication if chickenpox occurs.
See the Varicella Zoster Immune Globulin section for details on the recommended use of VariZIG in immunocompromised children, infants exposed to varicella around the time of birth and some hospitalized preterm infants.
Two vaccines containing varicella virus are licensed for use in the United States. Both vaccines contain live, attenuated varicella zoster virus (VZV) derived from the Oka strain.
- Varivax (VAR, Merck) contains only varicella vaccine virus.
- ProQuad (MMRV, Merck) is a combination measles, mumps, rubella, and varicella vaccine
Both vaccines may be administered either by subcutaneous injection or intramuscular injection. VAR is approved by the Food and Drug Administration (FDA) for people 12 months of age and older. MMRV is approved for people 12 months through 12 years of age. MMRV should not be administered to people age 13 years or older.
All children, beginning at age 12 months, as well as adults without other evidence of immunity should be vaccinated with 2 doses of varicella vaccine. Special consideration should be given to vaccinating adults who (1) have close contact with people at high risk for severe disease (e.g., healthcare workers and family contacts of immunocompromised people), or (2) are at high risk for exposure or transmission (e.g., teachers of young children; child care employees; residents and staff members of institutional settings, including correctional institutions; college students; military personnel; adolescents and adults living in households with children; non-pregnant women of childbearing age; and international travelers).
The Advisory Committee on Immunization Practices (ACIP) considers evidence of immunity to varicella to be:
- Written documentation of 2 doses of varicella vaccine given no earlier than age 12 months with at least 4 weeks between doses.
- U.S.-born before 1980*
- A healthcare provider’s diagnosis of varicella or verification of history of varicella disease
- History of herpes zoster, based on healthcare provider diagnosis or verification of disease history
- Laboratory evidence of immunity or laboratory confirmation of disease
*Note: Although there is only a very small chance of susceptibility, due to the potential for severe consequences from varicella infection, year of birth is not accepted as evidence of varicella immunity for healthcare personnel, immunosuppressed people, and pregnant people.
No. ACIP recommends giving a dose of MMR to infants age 6 through 11 months before international travel, but not varicella vaccine. Varicella vaccine is neither approved nor recommended for children younger than age 12 months in any situation.
Varicella vaccine is neither approved nor recommended for children younger than age 12 months. Assuming that the child is not immunocompromised, varicella zoster immune globulin (VariZIG) is also not recommended.
ACIP does not have a recommendation for acyclovir for varicella postexposure prophylaxis. The American Academy of Pediatrics provide some guidance on this issue in the current edition of the Red Book.
No. A healthcare provider’s diagnosis or verification of a history of shingles is acceptable evidence of immunity to varicella. According to ACIP, acceptable evidence of varicella immunity in healthcare personnel includes (1) documentation of 2 doses of varicella vaccine given at least 28 days apart, (2) history of varicella or herpes zoster based on clinician diagnosis, (3) laboratory evidence of immunity, or (4) laboratory confirmation of disease.
Recombinant zoster vaccine (RZV, Shingrix, GSK) does not count as the first of two doses of varicella vaccine. Shingrix is not licensed and has not been evaluated for the prevention of primary varicella infection. To meet the immigration requirements, you should give a dose of varicella vaccine now and a second dose at least 4 weeks later. The varicella vaccine doses will not be harmful and will allow your patient to meet the regulatory requirement.
Yes. For everyone whose varicella immunity is based on vaccination, 2 doses of varicella vaccine are recommended.
In the ten years following vaccine licensure in 1995, there was a significant decline in varicella disease, as well as varicella-related hospitalizations and deaths. Although a 1-dose regimen was estimated to be 80% to 85% effective, breakthrough disease was still occurring in highly vaccinated populations. A 2-dose regimen was adopted in 2006 to further reduce the risk of disease among vaccinated people whose numbers would accumulate over time, which could lead to varicella disease later in life when it can be more severe.
If the child had confirmed varicella disease or laboratory evidence of prior disease, it is not necessary to vaccinate regardless of age at infection. If there is any doubt that the illness was actually varicella, the child should be vaccinated.
It is critical to vaccinate susceptible older children and adults whenever the opportunity arises. With younger children being routinely vaccinated, the chance of being exposed to cases of chickenpox is decreasing. Older children, adolescents, and adults who have not had chickenpox now have a greater chance of remaining susceptible. These older individuals, when they contract chickenpox, are more likely to become seriously ill and have disease complications than younger children.
No. Shingles is caused by varicella zoster virus, the same virus that causes chickenpox. A history of shingles based on a healthcare provider diagnosis is evidence of immunity to chickenpox. A person who has had shingles does not need to be vaccinated against varicella. The person should still receive zoster vaccine, however, if it is not contraindicated and the person is age 50 or older or is age 19 or older and immunocompromised.
No. Receipt of one dose of live zoster vaccine is not proof of varicella immunity. According to CDC, acceptable evidence of varicella immunity in healthcare personnel includes (1) documentation of 2 doses of varicella vaccine given at least 28 days apart, (2) history of varicella or herpes zoster based on clinician diagnosis, (3) laboratory evidence of immunity, or (4) laboratory confirmation of disease. If a healthcare employee has received a dose of live zoster vaccine in the past but has no other evidence of immunity to varicella, the live zoster dose can be considered the first dose of the 2-dose varicella series. Note that recombinant zoster vaccine (RZV, Shingrix) cannot be counted as the first dose in a 2-dose varicella vaccination series because Shingrix is not licensed and has not been evaluated for the prevention of primary varicella infection (chickenpox).
Yes. In its 2018 recommendations for the prevention of herpes zoster, ACIP states that Shingrix may be used in adults age 50 years or older irrespective of prior receipt of varicella vaccine or live zoster vaccine (Zostavax, Merck). Shingrix is also recommended for adults age 19 and older who are immunocompromised due to disease or treatment if they have a history of varicella illness or vaccination.
A mild case of chickenpox produces immunity to varicella as does a moderate or severe case. A child with a reliable history of chickenpox does not need to receive varicella vaccine. However, if there is any doubt that the mild illness really was chickenpox, it is best to vaccinate the child. There is no harm in vaccinating a child who is already immune.
Varicella vaccine is most effective in preventing chickenpox or reducing the severity of the disease if used within 72 hours (3 days), and may still be helpful up to 5 days after exposure. However, not every exposure to varicella leads to infection, so for future immunity, varicella vaccine should be given to a person age 12 months or older who does not have a contraindication to vaccination, even if more than 5 days have passed since an exposure.