Varicella Activity Among Post-Secondary Students

Advisory Alert

March 9, 2018

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Re: Varicella Activity Among Post-Secondary Students

To our community health care providers,

I am writing to advise you of lab-confirmed cases of primary varicella infections occurring in unimmunized international students attending a local post-secondary institution from mid-January until early this month. Please have primary varicella infection on your differential when patients present to you with clinically compatible signs and symptoms. This Advisory Alert provides you with information on varicella etiology, clinical presentation and transmission, laboratory testing, vaccine considerations and reporting requirements.


Varicella is caused by varicella-zoster virus (VZV), a DNA virus that is a member of the herpesvirus group.

Clinical Presentation

The incubation period for varicella is typically 14 to 16 days post exposure to varicella or a herpes zoster rash, with a range of 10 to 21 days. A mild prodrome of fever and malaise may occur 1 to 2 days prior to onset of rash, particularly in adults. The rash is generalized and pruritic, first appearing on the head, chest and back and then spreading to the rest of the body. Progression is rapid from macules to papules to vesicles prior to crusting.

Infants, adults and immunocompromised persons are at higher risk for more severe disease and are at greater risk of complications from infection. Complications can include bacterial infection of the skin and soft tissues, pneumonia and, less commonly septicemia, toxic shock syndrome, necrotizing fasciitis, osteomyelitis, bacterial pneumonia and septic arthritis.

Breakthrough varicella is infection with wild-type VZV occurring in a vaccinated person > 42 days after varicella vaccination. Breakthrough varicella is usually mild with patients presenting as afebrile or with a low-grade fever and fewer than 50 skin lesions. Duration of illness is typically short and the rash is more likely to be predominantly maculopapular rather than vesicular. Approximately one quarter to one third of persons with a history of 1 dose of varicella vaccine who have breakthrough infection experience symptoms more typically associated with those who are unvaccinated.


Varicella is highly contagious and is spread from person-to-person by direct contact, inhalation of aerosols from vesicular lesions and possibly through infected respiratory secretions that may also be aerosolized. The period of communicability is as long as 5, but typically 1 to 2 days prior to rash onset until the lesions have crusted over. Contagiousness may be prolonged in individuals with altered immunity. Recovery from primary infection usually provides ongoing immunity.


Diagnostic testing includes serology and culture with current testing guidelines below:


Please ensure that clients presenting to you are immunized in accordance with the publicly funded immunization schedule. Susceptible household contacts of immunocompromised, immunodeficient and/or pregnant women should receive vaccination as appropriate for age and risk factors. Varicella vaccine administration to eligible susceptible persons within 3 to 5 days after exposure has been shown to be effective in preventing or reducing the severity of infection.…/immunization_schedule.pdf

Management of Cases and Contacts

Treatment of cases where appropriate is based on clinical indication. Health care workers (HCWs) with acute varicella illness must be excluded from work until lesions are dried and crusted. Varicella infection in pregnancy requires prompt treatment initiated within 24 to 48 hours of rash onset to prevent maternal and fetal sequelae.

Children in whom varicella disease occurred at <12 months of age should receive the routine two-dose varicella containing vaccine schedule.

Pregnant contacts should be advised to consult with their physician promptly to confirm history of varicella vaccination or disease. Varicella immune globulin (VarIg) should be offered if serologic testing shows no evidence of immunity. Although there is no assurance that administering VarIg to a pregnant contact will prevent congenital malformation in the fetus, it may modify maternal varicella severity.

Susceptible exposed HCWs with significant exposure are required to be excluded from any work in hospital from 10 days after the first exposure until 21 days after the last exposure. Contact with and exposure to dried scabs from varicella or zoster lesions does not constitute significant exposure.


Primary varicella infection is a reportable disease in Ontario. Report any suspect and confirmed cases to Public Health Sudbury & Districts for follow-up.

Should you have any questions, please contact the immunization program at 705.522.9200, ext. 301.

Ariella Zbar, MD, CCFP, MPH, MBA, FRCPC
Associate Medical Officer of Health and Director, Clinical Services

This item was last modified on April 4, 2024