Disease and vaccination rates Back to top

How serious a disease is varicella?

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 persons developed complications, about 10,000 persons required hospitalization and 100 people died each year from varicella. Varicella tends to be more severe in 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.

How is varicella transmitted and for how long is it contagious?

Chickenpox 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 chickenpox, or from direct contact with a sore from a person with shingles. People with chickenpox are infectious for at least 6-7 days after the appearance of spots and until all lesions are crusted over.

How are we doing as a nation in vaccinating children and adolescents against varicella?

From 1997 to 2005, vaccination with 1 dose of varicella vaccine increased from 26% to 88% among 19-35 month old children, according to the National Immunization Survey. In addition, as of May 2008, varicella vaccination requirements exist in all but two states either for children in child care settings, schools, or both. These are both remarkable achievements during the short period of time following the licensure of the vaccine in 1995.

Do all states have varicella vaccination requirements before school entry?

No. To find out which states have laws regarding varicella vaccine requirements, go to IAC's website at www.immunize.org/laws. In 2005, CDC recommended expanding the requirements to cover students in all grade levels. Government health agencies at the state level should take necessary steps, including developing and enforcing school immunization requirements, to ensure that students at all grade levels (including college) and children in child care centers are protected against varicella and other vaccine-preventable diseases.

How has widespread use of varicella vaccine in children impacted disease?

Substantial reductions in varicella morbidity and mortality have occurred following the licensure of vaccine. Information from three active varicella surveillance areas reported varicella cases had declined by approximately 85%, and varicella hospitalizations rates declined by approximately 70%.

What can be done to protect a patient without evidence of immunity who is exposed to varicella and is at high risk for severe disease and complications?

These patients should receive varicella zoster immune globulin (VZIG). If given within 96 hours of exposure, VZIG can modify or prevent clinical varicella disease. In 2006, an investigational VZIG product, VariZIG, became available to requestors from the sole authorized U.S. distributor, FFF Enterprises. Details on the use of VZIG may be found in the 1996 varicella ACIP statement (MMWR 1996; 45 [RR-11]:20-24), and details on the use of VariZIG can be found in the MMWR (MMWR 2006; 55[08]:209-210) found at www.cdc.gov/nip/publications/ACIP-list.htm

General information Back to top

For whom is varicella vaccination recommended?

All children, beginning at age 12 months, as well as adults without other evidence of immunity (see next question) should be vaccinated with 2 doses of varicella vaccine. Special consideration should be given to vaccinating adults who (1) have close contact with persons at high risk for severe disease (e.g., healthcare workers and family contacts of immunocompromised persons), 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 childrearing age; and international travelers).

What are the criteria for evidence of immunity to varicella?

ACIP considers evidence of immunity to varicella to be

• Documentation of 2 doses of vaccine given no earlier than age 12 months, with at least 3 months between doses for children younger than age 13 years, or at least 4 weeks between doses for persons age 13 years and older •   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 •   Laboratory evidence of immunity or laboratory confirmation of disease     *Note: year of birth is not considered as evidence of immunity for healthcare personnel, immunosuppressed persons, and pregnant women.

Please review the newest recommendations for routine second doses of vaccine for everyone, including children.

In June 2006, ACIP voted to recommend that all children be given 2 doses of varicella vaccine routinely. The first dose should be given at age 12-15 months and the second dose at age 4-6 years. ACIP also recommended "catch-up" vaccination with a second dose for all adolescents and adults who may have missed a second dose. For children ages 12 months through 12 years, the minimum interval between doses is 3 months; for persons age 13 years and older, the minimum interval is 4 weeks.

Concerning the new recommendation for a second dose of varicella vaccine, does CDC recommend that children who received 1 varicella vaccine dose 10 years ago (when they were preschool age) get a second dose now?

Yes. The current recommendation is for 2 doses regardless of age, for anyone school age and older without evidence of immunity. For everyone whose varicella immunity is based on vaccination, 2 doses of varicella vaccine are recommended.

Why did ACIP revise its recommendations to add a second dose of varicella vaccine for all children?

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%-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 persons whose numbers would accumulate over time, which could lead to varicella disease later in life when it can be more severe.

Should a child who has had chickenpox prior to the first birthday get the first dose of varicella vaccine at age 1 year?

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.

How important is it to vaccinate older children and adults?

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.

How safe is varicella vaccine?

Varicella vaccine is very safe. About 20% of vaccine recipients will have minor injection site complaints, such as pain, swelling, or redness. Less than 5% of recipients develop a localized or generalized varicella-like rash 5-26 days after vaccination. These rashes have an average of 2-5 lesions, and may be maculopapular rather than vesicular. Fever following varicella vaccine is uncommon.

If a child has a very mild case of chickenpox (e.g., only 5-10 pox), is s/he immune or should s/he be vaccinated?

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.

If a child had 1 varicella vaccination and developed a vesicular (chickenpox-like) rash at the vaccination site 7 to 10 days after vaccination, does the patient still need the second dose? What if the rash covered the entire body?

If you believe the child had varicella disease (that is, breakthrough varicella) after the first dose, the child does not need another dose. If you are uncertain whether the child had varicella, the second dose should be administered on schedule. If in doubt, plan to give the second dose. If this was a case of breakthrough varicella, a second dose will not be harmful.

If a child breaks out in 5-10 maculopapular spots 2 weeks following varicella vaccination, can s/he go to school?

Transmission of varicella vaccine virus is a rare event, and appears to occur only when the vaccinated person develops a vesicular rash. A maculopapular rash 2 weeks after varicella vaccine may not have been caused by the vaccine. If the rash were caused by the vaccine, the risk of transmission is very small; however, the child should avoid close contact with persons who do not have evidence of varicella immunity and who are at high risk of complications of varicella, such as immunocompromised persons, until the rash has resolved.

If a vaccinated child gets 5-10 vesicular lesions 2 weeks after vaccination, can s/he attend school?

You cannot distinguish a mild case of varicella disease from a rash caused by the vaccine. The child may have been infected with varicella at about the same time s/he was vaccinated. The conservative approach would be to treat the child as if s/he had chickenpox and restrict her/his activities until all the lesions crust over.

If a child gets breakthrough varicella infection, ~50 lesions, can s/he go to school?

Breakthrough varicella represents replication of wild varicella virus in a vaccinated person. Although most breakthrough disease is very mild, the child is contagious and activities should be restricted to the same extent as an unvaccinated person with varicella disease.

Can my four-year old, who was recently vaccinated for chickenpox, spread the vaccine virus to other household members?

Available data suggest that healthy children are unlikely to transmit vaccine virus. Transmission of vaccine virus to a household contact has rarely been documented. It appears that transmission of vaccine occurs mostly, or perhaps even exclusively, when the vaccinated person develops a rash following vaccination.

I understand that varicella vaccine can be used in postexposure settings. How soon after exposure does the vaccine need to be given?

Varicella vaccine is effective in preventing chickenpox or reducing the severity of the disease if used within 72 hours (3 days), and possibly up to 5 days, after exposure. However, not every exposure to varicella leads to infection, so for future immunity, varicella vaccine should be given, even if more than 5 days have passed since an exposure.

An 8-month-old was erroneously given varicella vaccine. What might the consequences be? What should we do now?

An 8-month-old is likely to have residual passive varicella antibody from his or her mother. The vaccine probably will have no effect, and no action is necessary. The dose should not be counted, and the child should be revaccinated at 12-15 months of age.

Does varicella vaccine affect mantoux readings in the same way that MMR does?

There is currently no information on the effect of varicella vaccine on reactivity to a tuberculin skin test (PPD). Until information is available, it is prudent to apply the same rules to varicella vaccine as are applied to MMR: PPD may be applied before (preferably) or simultaneously with varicella vaccine. If vaccine has been given, delay the PPD for at least 4 weeks.

Scheduling and serology Back to top

What is the recommended schedule for vaccinating a child? What about adults?

For infants, the first dose should be given at age 12 months with a second dose given at age 4-6 years. The second dose could be given earlier, if necessary, as long as there is a 3-month interval between doses. All other children age 13 years and older as well as adults without evidence of immunity should also have documentation of 2 doses of varicella vaccine, separated by a minimum interval of 4 weeks.

Many children in my practice have had only 1 dose of varicella vaccine. Is there a problem waiting until the 11- to 12-year-old visit to give them the second dose?

Don't delay giving the second dose of varicella vaccine. Give the second dose the next time the child or teen is in your office. The recommendation to routinely give a second dose at age 4-6 years is intended to provide improved protection in the 15-20% of children who do not adequately respond to the first dose.

What should we do if a child younger than age 13 years was given a second dose with only a 4 week interval?

ACIP recommends that if the interval was at least 28 days it doesn't need to be repeated.

Under what circumstances should I obtain a varicella titer after vaccination?

Postvaccination serologic testing is not recommended in any group, including healthcare workers.

Which of my patients should have varicella serology prior to receiving varicella vaccine?

ACIP does not recommend serologic testing for persons younger than age 13 years. At least 90% of adolescents and adults from the U.S. can be expected to be immune to varicella, including those who do not recall having had the disease. As a result, serologic screening may be considered for persons age 13 years and older who do not have a history of chickenpox, a strategy that may be cost effective, depending on the cost of the serologic test. However, it is safe to give varicella to persons already immune to the disease, so screening is not required under any circumstance.

Should I test women for varicella immunity at their first prenatal visit?

Test pregnant women who lack either (1) documentation of receipt of 2 doses of varicella vaccine or (2) healthcare-provider diagnosis or verification of varicella or herpes zoster disease. Women who are not immune should begin the 2-dose vaccination series immediately postpartum.

What is the appropriate lab test to use to determine whether there has been previous chickenpox disease?

Commercially available laboratory tests for varicella antibody are usually based on a technique called EIA (enzyme immunoassay). Though these tests are sufficiently sensitive to detect antibody resulting from varicella zoster virus infection, they are generally not sensitive enough to detect vaccine-induced antibody. The more sensitive assays needed to detect vaccine-induced antibody are not widely available. This is why CDC does not recommend antibody testing after varicella vaccination.

Precautions and contraindications Back to top

What are the recommendations for the use of varicella vaccine in children with HIV or other immunodeficiencies?

ACIP recommends varicella vaccination of children with humoral (but not cellular) immunodeficiencies. In addition, vaccination should be considered for children with HIV infection in CDC class N, A, or B who have CD4+ T-lymphocyte percentages of 15% or higher. For additional details of these recommendations, click here.

If a person develops a rash after receiving varicella vaccination, does he need to be isolated from susceptible persons who are either pregnant or immunosuppressed?

Transmission of varicella vaccine virus is rare. However, if a pregnant or immunosuppressed household contact of a vaccinated person is known to be susceptible to varicella, and if the vaccinee develops a rash 7-21 days following vaccination, it is prudent that they avoid prolonged close contact with the susceptible person until the rash resolves.

After receiving varicella vaccine, should healthcare personnel avoid contact with immunocompromised patients?

No. This is not necessary unless the person who was vaccinated develops a rash.

Is there any concern when giving varicella vaccine to a child who lives with a susceptible pregnant woman or an immunocompromised individual?

ACIP recommends varicella vaccine for healthy household contacts of pregnant women and immunosuppressed persons. Although there may be a small risk of transmission of varicella vaccine virus to household contacts, the risk is much greater that the susceptible child will be infected with wild-type varicella, which could present a more serious threat to household contacts.

I am breast-feeding my six-month old baby. May I receive varicella vaccine without the risk of transmitting the vaccine virus to her?

Yes. There have been no reports of mother to child transmission of varicella vaccine virus. However, transmission of vaccine virus to household contacts has been documented so transmission to a breast-fed infant from its vaccinated mother is at least theoretically possible. If the susceptible mother were to be infected with wild varicella virus, the risk of transmission to the infant would be much higher. So, if the mother is at high risk of exposure to varicella, the benefits of vaccination probably outweigh the risk of transmission to the infant.

Vaccine and pregnancy Back to top

What are the recommendations for varicella vaccination before and after pregnancy?

Live varicella vaccine should not be given to a woman who is known to be pregnant or who plans to become pregnant within one month. If a woman who is planning to become pregnant in the future comes in for a visit or an annual exam, her varicella history should be obtained and if indicated, 2 doses of vaccine should be given, spaced 4-8 weeks apart. Pregnant women should be assessed for evidence of varicella immunity and if non-immune, should receive the first dose of varicella vaccine following termination or completion of the pregnancy and prior to hospital discharge. A second dose should be given 4-8 weeks later.

Can a pregnant healthcare worker with a history of varicella infection care for a patient with varicella? Is it possible for her to have a declining titer, thus making her susceptible to the virus again?

Persons with a reliable history of varicella can be considered to be immune. A reliable history would consist of (1) a healthcare provider's diagnosis of varicella or verification of history of varicella disease; (2) a history of herpes zoster, based on healthcare provider diagnosis; or (3) laboratory evidence of immunity or laboratory confirmation of disease. Immunity following disease or vaccination is probably life-long. More than one primary infection with varicella is unusual.

Should all pregnant women have serology screening for varicella?

No. Serologic testing for varicella should be considered only for women who do not have evidence of immunity (reliable history of chickenpox or documented vaccination). Once a person has been found to be seropositive, it is not necessary to test again in the future.

If a woman receives varicella vaccine, how long should she wait before becoming pregnant?

Contrary to the information provided in the package insert (3 months), the ACIP recommends that a wait of 1 month is sufficient.

If a woman receives varicella vaccine and subsequently finds out that she is pregnant, what should she be told about the risk to the fetus?

There is no information available concerning the risk to a fetus if a pregnant woman is inadvertently given varicella vaccine. However, the risk of congenital varicella syndrome following varicella disease is small, so the risk of congenital anomalies following vaccination with live attenuated varicella vaccine is probably very small. In order to clarify this risk, CDC and Merck have established a Varicella Vaccination in Pregnancy registry, similar to that which was established for rubella vaccine inadvertently given during pregnancy. Healthcare providers are encouraged to report such incidents by calling the Registry at (800) 986-8999.

Vaccine storage and handling Back to top

How should varicella vaccine be stored in my clinic?

Varicella vaccine must be kept frozen at a temperature of +5°F (-15°C) or colder until it is reconstituted. Most relatively new frost-free freezers will maintain this temperature but older dormitory-style refrigerators without a separate freezer compartment are not adequate. Freezer temperature must be carefully checked prior to ordering the vaccine. The diluent should be kept separately in the refrigerator or at room temperature. The vaccine must be administered within 30 minutes of reconstitution.

What happens if you put varicella vaccine in the refrigerator instead of the freezer?

It's possible that the vaccine could be damaged if not stored according to the manufacturer's instructions. However, it may still be possible to use the vaccine. Put the affected vaccine vials back into the freezer after you have marked them so that they are not confused with the unaffected vials, then call the Merck Vaccine Division at 800-9-VARIVAX right away. Merck will make a recommendation regarding whether the vaccine is still usable, and if so, give you a new expiration date. Do not administer the vaccine until you have consulted with Merck. Similarly, if you have inadvertently left your vaccine at room temperature instead of in the freezer or have experienced a power failure, the same instructions apply.

How can I transport varicella vaccine to a clinic that doesn't have a freezer?

Varicella vaccine is less stable than other vaccines you routinely handle. Varicella vaccine must be stored at 5°F (-15°C) or less in order for the expiration date printed on the package to be valid. Potency of the vaccine begins to decline within minutes of being exposed to temperatures above 5°F. Consequently, the vaccine should be kept at freezer temperature at all times, including during transport between clinics. Temperature can be maintained by transporting the vaccine in the original shipping container (or a container of comparable insulating quality) with an adequate amount (at least 6 pounds) of dry ice. If dry ice is not available the vaccine may be stored at refrigerator temperature 36-46°F (2-8°C) for up to 72 hours. However, once the vaccine has been removed from the freezer it should not be refrozen, and must be discarded after 72 hours at refrigerator temperature. Do not, under any circumstances, use varicella vaccine that has been out of the freezer for more than 72 hours unless it has been kept on dry ice continuously. If you discover varicella vaccine in the refrigerator, and cannot determine exactly how long it has been there, the vaccine must be discarded. Never risk giving your patients varicella vaccine that has been mishandled. If your vaccine supply has been thawed because of a catastrophic event, such as a power failure, it may still be potent enough to use. Keep the vaccine cold and estimate the temperature to which the vaccine was exposed. You must then contact the Merck Vaccine Division (800-9-VARIVAX) to determine if the vaccine is still usable. If the vaccine was purchased with state or federal funds, you should also contact your state immunization program as soon as possible.

Reviewed on 6/09