VACCINE RESOURCE COMMITTEE

of the Edmonton Zone Medical Staff Association

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measles, mumps, rubella and varicella Vaccine Question #3:

Does getting chickenpox lead to better immunity than the vaccine?

Some people think natural infection (getting chickenpox disease) is better than getting the vaccine but getting the chickenpox vaccine is much safer than getting the disease.

The chickenpox vaccine is significantly safer and more effective than getting the chickenpox disease itself, offering protection against severe illness and complications.

The rate of breakthrough varicella disease in vaccine recipients following one dose of univalent varicella vaccine has been estimated at 7.2% over a 10 year follow-up period. A two dose primary schedule for children 12 months to 12 years of age has shown to reduce the cumulative risk of breakthrough disease 3.3-fold compared to children who received only one dose. The estimated vaccine effectiveness 10 years following the receipt of two doses of univalent varicella vaccine is estimated at over 98% against any varicella disease and 100% against severe varicella.

There are no data regarding the long-term effectiveness of MMRV vaccine.

A review of data from the Canadian Institute for Health Information for 1994 to 2000 showed that over 1,550 varicella hospitalizations occur annually for all age groups. Information on pediatric hospitalized cases and deaths are available from the Immunization Monitoring Program, ACTive (IMPACT) These data indicate that the majority of hospitalizations occur in previously healthy children.  Since the public funded vaccine programs began in 2004 in Canada, the annual hospitalizations of varicella dropped from 288 (1999 to 2004) to 114 (2005-2009).

More severe disease and serious complications from chickenpox can occur in any person who develops chickenpox, although they are more common in babies, teenagers, adults, pregnant women and those with weakened immune systems.  

The complications of varicella include secondary bacterial skin and soft tissue infections, otitis media, bacteremia, pneumonia, osteomyelitis, septic arthritis, endocarditis, necrotizing fasciitis, toxic shock-like syndrome, hepatitis, thrombocytopenia, cerebellar ataxia, stroke and encephalitis. Varicella increases the risk of severe invasive group A streptococcal infection in previously healthy children by 40- to 60-fold. Complications are more common in adolescents, adults and immunocompromised people, who have higher rates of pneumonia, encephalitis and death.

A non-immune pregnant woman who develops primary varicella infection during pregnancy may cause congenital varicella syndrome in the fetus. It is rare when infection occurs before the 13th or after the 20th week of gestation. The risk is approximately 2% when infection occurs at 13-19 weeks of gestation. Congenital infection results in a wide clinical spectrum, which may include low birth weight, ophthalmic abnormalities, skin scarring, limb atrophy, cerebral atrophy and a variety of other anomalies. Almost one-third of affected infants die by early in the second year of life. Maternal varicella occurring in the 5 days before to 2 days after birth is associated with severe neonatal varicella in 17% to 30% of infants, with high case fatality for the newborn.

Varicella case fatality rates are highest among adults (30 deaths/100,000 cases), followed by infants under 1 year of age (7 deaths/100,000 cases) and then those aged 1 to 19 years (1-1.5 deaths/100,000 cases). Since 2000, a total of 11 pediatric deaths due to varicella were reported by IMPACT with a range of zero-three deaths per year.

Following the initial varicella illness, varicella-zoster virus establishes latency in the sensory nerve ganglia, which may be reactivated later in life as herpes zoster (also known as shingles).

Sources:

Health Link BC: Chickenpox (varicella) vaccine
Government of Canada: Varicella (chickenpox) vaccines: Canadian Immunization Guide
Government of Canada: Varicella (Chickenpox)