Posted June 7, 2023. Past health advisories and alerts are archived for historical purposes and are not maintained or updated.
Summary
Over the past weeks, there has been a notable rise in breakthrough varicella cases throughout Spokane County. These cases primarily involve children who have received one or both doses of the varicella vaccine. Breakthrough varicella cases may present with atypical, milder symptoms. There may be fewer skin lesions, and these lesions can easily be mistaken for bug bites or other rash illnesses. When vaccination status makes clinical diagnosis of varicella complicated, it is recommended to PCR test the skin lesions. Breakthrough varicella cases can transmit the virus to others and are subject to the same exclusions from schools and day care as unvaccinated cases.
Background
The varicella vaccine is highly effective: the effectiveness against clinical varicella after one dose of varicella vaccine is estimated to be 82% and 98% after two doses. According to the Centers for Disease Control and Prevention (CDC) about 15 to 20 percent of people who have received one dose of chickenpox vaccine do still get chickenpox, and children who received two doses of the vaccine were three times less likely to get the disease than those who only had one dose. As vaccine coverage increases, the proportion of varicella cases who are vaccinated has increased, with 69% of cases in 2008 being among vaccinated persons. Vaccinated cases typically have a milder presentation which includes:
While the cases are typically milder, it is still possible for cases to transmit the virus to others. Persons with chickenpox are contagious for one to two days before the rash appears and continue to be contagious until all the blisters are crusted over, usually in four to seven days after rash onset.
Recommendations for Clinicians
When varicella rash is suspected in a fully vaccinated case, it is best to confirm diagnosis with laboratory PCR testing of scabs, vesicular fluid, or scrapings of maculopapular lesions. Children suspected of varicella infection should be excluded from schools, childcare, and other group settings until all blisters have crusted over. Vaccinated children may develop lesions that do not crust. These children should be isolated until no new lesions appear within a 24-hour period.
Resources
Do You Know What Breakthrough Varicella (Chickenpox) Looks Like?
