How common is chickenpox?
Chickenpox is highly contagious and very common, with a secondary attack rate in households of 85 - 90%. It is primarily a disease of young children and is most common in school aged children between 5 and 9 years of age when approximately 50% of cases occur. Only 10% of cases occur in adolescents older than 15 years of age and it is estimated that 95% of people have been infected by 30 years of age.
What are the complications of chickenpox in normal children?
The most common complication of chickenpox is secondary bacterial infection with Group A Streptococcus Pyogenes and Staphylococcus Aureus that occurs in 5 to 10% of children. Bacterial infection should be suspected whenever redness and swelling occur around a pox lesion that is enlarged in size. Because cellulitis may follow a local infection, prompt empirical therapy with oral antibiotics such as cloxacillin or cephalexin is indicated. Otitis media may also complicate chickenpox and has been reported to occur in about 5% of children. More serious complications of chickenpox are rare and hospitalization is indicated in only 1 in 5,000 cases. Severe complications include pneumonia, encephalitis, cerebellar ataxia, Reye's syndrome, Guillain - Barre syndrome, nephritis, carditis, arthritis, orchitis, uveitis, thrombocytopenia, hemorrhagic chicken pox and purpura fulminans.
When can children return to school?
This has been a controversial issue for sure, but ought not to be. The latest word from the Canadian Pediatric Society, which restates it's 1994 recommendation (Can J Infect Dis 10;193-196, May/June 1999) is that children with mild varicella should be allowed to return to day care or school as soon as they feel well enough to participate normally in all activities, regardless of the state of the rash. Mild chicken pox is defined as having a low fever for a short period of time and fewer than 30 spots. Many of these children are 'well' by the second or third day of the illness and can participate in regular activities. The decision to return to school therefore should be based on individual facts and circumstances. As you indicated, many schools and day care centres still have strict exclusion policies that that keep children with varicella at home for 5 days after the rash appears (and some schools keep them home even longer, until the vesicles are completely dried). The reasoning behind the CPS position statement is that varicella is contagious from two days before the rash appears and is believed to be most infectious from 12 - 24 hours before the rash is recognized. Since the goal of exclusion is to protect other children from developing varicella, by the time the rash has appeared it is already too late to prevent the spread. Is varicella worth preventing with the varicella vaccine?In the United States 3 million cases of varicella are reported a year and it is estimated that approximately 150,000 - 200,000 cases of these become complicated. Approximately 100 deaths per year are attributed to varicella. Varicella vaccine was licensed in the USA in 1995 and is purportedly cost effective if one takes into account the cost of parental work time lost in addition to all other factors related to varicella. However, do medical costs alone provide an economic justification for varicella vaccination?
Will varicella vaccine give complete and long lasting protection?
Consolidated experience for 10 years shows that about 70-80% of vaccinees will have complete protection and the remaining vaccinees will have partial protection against clinical illness. The vaccine is apparently 95% effective against severe varicella, the disease that predisposes an individual to the frequent complications of bacterial superinfection. It is not yet known however whether rarer complications to varicella, such as pneumonia encephalitis or hepatitis will be prevented. In Japan, where 20 year follow-up studies have been conducted, there is evidence for persistent immunity and at this time it appears that there is no evidence for waning post-vaccination protection. The concern is of course that if immunity wanes over time, these individuals will become fully susceptible to chickenpox and the effect of vaccination might have a negative outcome by shifting the disease from children to adults.
Will the vaccine reduce the risk of zoster?
Zoster may occur in individuals vaccinated but the reported cases have been mild and the rate has been less than in age-matched control patients after natural varicella infection. The choice between having a latent natural virus or latent vaccine virus in the ganglia causing zoster seems to favor the latter.
Is there a risk that the vaccine virus will be transmitted to healthy contacts?
The varicella virus is present in the vesicular lesions that occur in some vaccinees and mild varicella has been transmitted from children with leukemia to their healthy contacts. There has also been a report of a pregnant woman who was infected from her vaccinated healthy child. Unlike MMR, the manufacture of varicella vaccine advises against vaccinating children in contact with pregnant women.
What is the bottom line regarding varicella vaccine in Canada?
The vaccine is now currently available in Canada. The vaccine no longer needs to be kept frozen before use as a product which is refrigerator stable for ninety days has now been released.
What are the current Canadian recommendations to prevent severe varicella in children and adolescents?
Current recommendations are to use VZIG (Varicella zoster immune globulin) alone or in combination with a acyclovir in high risk patients. These would include such patients as immuno-compromised children and susceptible newborns (infants born to mothers who developed varicella within 5 days of delivery or 2 days after delivery). Adolescents and adults are at greater risk for developing severe chicken pox and should be treated with oral acyclovir at the first sign of varicella lesions.
| PEARLS |
|---|
| Chicken pox is highly contagious and very common particularly in school-aged children. |
| The most common complication of varicella is secondary bacterial infection. |
| Varicella vaccine was licensed in the USA in 1995 and is now currently available in Canada |
| Problems with the vaccine; thermal instability, duration of immunity and transmission to others.. |
Key References:
CPS Statement, Chickenpox: Prevention and treatment, Can J Paed, 1994; 1:88-93
Plotkin S, Varicella Vaccine, Pediatrics, 1996; 97: 251-252
July, 1996
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