1. What kind of vaccine is varicella? What is its dosage schedule?

Varicella vaccine is a live attenuated virus vaccine that is administered subcutaneously. For children through age 12 years, it is administered subcutaneously as a single 0.5ml dose. Persons 13 years of age and older should receive two 0.5ml doses subcutaneously 4-8 weeks apart.

2. Can the varicella vaccine be given at the same time as other vaccines?

Yes, varicella vaccine can be given at the same time as other vaccines given routinely in childhood. It is recommended that for children 12-18 months of age, the varicella vaccine be given at the same time as MMR vaccine or, when administered separately, MMR and varicella vaccine should be given at least 28 days apart.

3. How effective is the varicella vaccine in preventing varicella disease?

Pre-licensure studies of varicella vaccine showed the vaccine to be 70-90% effective in preventing disease and more than 95% effective in protecting against severe disease. If a vaccinated person does get varicella, it is usually a very mild case with fewer lesions (usually <50, which are frequently not vesicular), mild or no fever, and a quicker recovery. Investigations of vaccine field effectiveness since vaccine licensure have demonstrated that vaccine provides 100% protection against moderate to severe disease and most commonly is effective in preventing 80-90% of all disease. These data indicate that the vaccine performs well under conditions of community use.

4. Is waning immunity a problem with the varicella vaccine?

The length of protection/immunity from any new vaccine is never known when it is first introduced. Available data from following up children vaccinated in prelicensure clinical trials indicate that protection from varicella vaccine lasts for at least 25 years (Japanese data) and 14 years (U.S. data). Experience with other live viral vaccines (e.g. measles, rubella) has shown that post vaccination, immunity remains high throughout life. For these vaccines, second doses are needed to cover the small percent of people who fail to seroconvert after the first dose (primary vaccine failure). Follow-up studies continue to assess levels of immunity in vaccines as disease incidence declines.

5. Will a booster vaccination be needed in the future?

Ongoing studies and surveillance will determine the need for, and if appropriate, the timing of additional doses in the future. At this time, there is no recommendation for a booster dose.

6. How will use of varicella vaccine affect the epidemiology the disease?

As all vaccines have done, varicella vaccine will affect the epidemiology of the disease. Most importantly, the incidence of disease will decline in all age groups. This is already occurring in sites conducting active surveillance for varicella. In 1999, there was a dramatic decline in cases and the expected spring time increase in varicella cases did not occur. As we would expect, the greatest decline in incidence has occurred among children 1-4 years; however, the decline in incidence is occurring in all age groups, including adults who currently do not have recommendations for varicella vaccine and infants < 12 months who are not eligible for vaccination. As transmission continues to decline, decreasing circulation of wild virus will increase the likelihood that unexposed and unvaccinated children will enter adolescence and adulthood without immunity. Thus, it is increasingly important to offer vaccine to all susceptible adolescents and adults as well as children in line with current recommendations. The Advisory Committee on Immunization Practices (ACIP), American Academy of Pediatrics (AAP), and American Academy of Family Physicians (AAFP) recommend vaccination at 12-18 months and catch-up vaccination of all susceptible children and adolescents in order to prevent outbreaks at older ages, when disease is more severe, among older children who are neither vaccinated nor exposed to wild type virus.

7. Should serologic testing be done prior to vaccination?

A reliable history of varicella is considered presumptive evidence of immunity. However, if an adult has a negative or uncertain history of varicella, testing is likely to be more accurate than relying on history alone, since 70% to 90% of adults who do not have a reliable history of varicella are actually immune. Thus, serologic testing before vaccination is likely to be cost-effective since the cost of a lab test ($25-$75) is usually less than vaccination (approximately $100 for two doses of vaccine). Depending on the cost of the laboratory test it may also be cost-effective to determine the serologic status of older children with negative or uncertain histories of varicella prior to vaccination. However, testing is not required and the vaccine is well-tolerated in persons who are immune.

8. What laboratory tests are available to determine varicella immunity prior to vaccination?

   The most common commercially available test is the EIA (enzyme immunoassay). This test is sensitive enough to determine immunity following natural disease, but may not be sensitive enough for determining immunity following vaccination when antibody levels are lower. The serology test used to determine immune response to varicella vaccine during the clinical trails, the gpELISA test, is not available commercially. Thus, serological results obtained following vaccination must be interpreted with caution since some commercially available tests are not sensitive enough to detect low levels of antibody post-vaccination. Other tests with higher sensitivity than the commercially available EIA such as the FAMA (flourescent antibody-to-membrane antigen) assay requires extensive experience and is performed only in a few academic laboratories. A VZV latex bead agglutination assay is now commercially available that is more sensitive than most conventional EIAs.

9. What adverse events are associated with varicella vaccine?

Varicella vaccine is very safe. Although vaccine recipients in uncontrolled trials reported minor injection site complaints (20% reported pain, swelling or redness) and rashes (3%-5% reported a localized rash, and an additional 3%-5% developed a generalized varicella-like rash 5-26 days after vaccination), the rate of adverse events was much lower in the only randomized, controlled clinical trial conducted in children. In this trial 1% of vaccine recipients developed injection site rash compared with 0.3% of placebo recipients and 3.2% of vaccine recipients developed generalized rash compared with 1.7% of placebo recipients. These rashes had an average of 2-5 lesions and were likely to be maculopapular rather than vesicular. The incidence of fever did not differ between the vaccination and placebo groups. Experience with the first 11 million doses distributed show that very infrequently (in approximately 2.8 per 100,000 doses given) serious adverse events such as seizures, encephalitis, pneumonia, anaphylaxis and death have occurred. Note: Reporting a serious adverse event after vaccination does not indicate a causal association between vaccination and the event. Physicians should report serious adverse events to the Vaccine Adverse Event Reporting System (VAERS) at 1-800-822-7967.

For more information, visit the following site:
http://vaers.hhs.gov

Updated ACIP recommendations:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm

10. For serious adverse events that occur after varicella vaccination, are there laboratory methods that distinguish the vaccine virus from the wild virus?

Yes, CDC’s National VZV Laboratory provides VZV strain discrimination testing to state and local public health organizations and to private physicians in cases of suspected adverse events following vaccination. The laboratory offers free testing for suspected adverse events such as:

• Individuals who develop > 50 lesions 7-42 days post vaccination;
• Individuals who develop certain serious adverse experiences post vaccination including pneumonia, pneumonitis, cerebritis (encephalitis), cerebellitis (cerebellar ataxia) and aseptic meningitis;
• Herpes zoster post vaccination;
• Suspected cases of secondary transmission of the vaccine virus;
• Pregnant women who inadvertently receive varicella vaccine or who have been exposed to a vaccinee and who develop a varicella rash.

The contact phone number at the National VZV Laboratory for information on this service including how to collect and transport specimens is (404) 639-0066.

The National VZV Laboratory is also equipped to provide VZV serological testing and VZV diagnostic testing including strain discrimination for cases of severe disease or death believed to be related to VZV infection, and for suspected breakthrough infections with VZV and for VZV outbreaks.

11. What are the contraindications and precautions to varicella vaccination?

Varicella vaccine should not be given to persons who are allergic to any component of the vaccine or who have had a severe allergic reaction to a prior dose of vaccine. The vaccine contains neomycin and gelatin, but does not contain preservatives or egg protein.

Although the vaccine is not licensed for persons with blood dyscrasias, leukemia, lymphoma or malignant neoplasms affecting the bone marrow or lymphatic system, the vaccine is available at no cost for a limited group of patients with acute lymphoblastic leukemia (ALL) through a research protocol. In 1999, ACIP altered its recommendations for the use of varicella vaccine. The committee continued to contraindicate the vaccine for persons with cellular immunodeficiences but removed the restriction on vaccination of persons with defects of humoral immunodeficiency. In addition, ACIP suggested that physicians consider vaccinating a subset of HIV-infected children who are in CDC Class N1 or A1 and have an age-specific CD4% >25%. These children should receive 2 doses of the vaccine separated by 3 months.

As was previously recommended, the following groups of persons should not be vaccinated:

• persons taking large doses of corticosteroids (>2mg/kg of body weight or >20mg/day of prednisone or its equivalent);
• persons with a moderate or severe concurrent illness;
• women who are pregnant;
• persons who have received blood products (such as whole blood or immune globulin) during the previous 5 months;
• and persons with a family history of congenital hereditary immunodeficiency in first degree relatives unless they are known to be immunocompetent.

Caution is advised when immunizing children receiving salicylates. No adverse events associated with the use of salicylates after varicella vaccination have been reported. However, the vaccine manufacturer recommends that vaccine recipients avoid using salicylates for 6 weeks after receiving varicella virus vaccine because of the association between aspirin use and Reye syndrome following varicella. Vaccination with subsequent close monitoring should be considered for children who have rheumatoid arthritis or other conditions requiring therapeutic aspirin.

For further information, visit the following site:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm

See also Recommendations for Postexposure Prophylaxis of Varicella of Persons at High Risk for Severe Disease

12. What data are available concerning transmission of varicella vaccine virus to contacts?

Available data suggest that the risk of vaccine virus transmission from healthy vaccinees is very low and occurs only if the vaccinee has a rash. With the currently licensed vaccine, there have been 3 documented cases of transmission from healthy vaccinated children. The risk for transmission from vaccinees who are immunocompromised is higher.

13. Will post-exposure use of the vaccine prevent or modify varicella?

    Yes, the vaccine may prevent or modify illness when administered within 3 to 5 days after exposure. The ACIP now recommends vaccination of susceptible persons who are eligible for vaccination as soon as possible after exposure--ideally within 3 days but possibly up to 5 days of an exposure--to prevent illness or modify disease severity. If a person has already been infected, and the vaccine is given soon enough, disease may be modified or prevented. If the person was infected >5 days prior to vaccination, there is unlikely to be any benefit from vaccination but vaccination is not known to be harmful. Finally, exposure even in a household setting does not result in transmission 100% of the time. So, if the exposed person has not been infected, vaccination will confer protection against subsequent exposures.

    For further information, visit the following site:
    http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm

14. Can vaccination be used to control outbreaks of varicella?

Varicella outbreaks in closed settings (e.g. child care centers, schools, institutions) tend to be protracted and go through several generations of infection before coming to an end in the absence of an intervention. School outbreaks have been documented to last for 3-6 months. Varicella vaccine has been used successfully by state and local health departments and by the military for outbreak prevention and control. Although the vaccine works by preventing illness or modifying the severity of illness in those vaccinated within 3 days and possibly up to 5 days after exposure, most of the benefit of vaccinating all susceptible individuals in an outbreak in a closed setting derives from vaccinating persons before exposure, since few individuals are actually infected in the first generation. For this reason, although it is desirable to intervene as early in an outbreak as possible, it is still useful to intervene at any point after the outbreak has been recognized and before all susceptible individuals have contracted illness. Intervening with vaccination can decrease the number of cases in an outbreak and shorten the outbreak’s duration.

For further information, visit the following site:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm