With the exception of one child (case 3), all of the children were thought to have normal immune function. Each of the five children older than one year of age had a chronic health problem not associated with immunodeficiency, although a subtle immune defect cannot be excluded. In our previous review of 861 VZ cases (1
), children with chronic conditions more often required intensive care and died than did previously healthy children (4% versus 0.2%, respectively). The children with health problems in the present report were most likely in frequent contact with health professionals; despite this, however, none of the children received VZ vaccine. The two children younger than one year of age (ie, too young to immunize) would have been spared if susceptible older household members had received VZ vaccine instead of developing chickenpox. All seven cases occurred before implementation of the routine VZ vaccination program in their home province. Thus, although VZ vaccine was available, a lack of public funding limited uptake (2
). Greater uptake of vaccine in public programs in 2003 and 2004 may account for the absence of fatal cases during these years.
Bacterial sepsis was the fatal complication in four of the seven cases, involving S pneumoniae
, group A streptococcus and Staphylococcus aureus
. The pneumococcal infection occurred before the availability of pneumococcal conjugate vaccine and is a reminder that VZ virus replication in the upper airway predisposes to otitis media, pneumonia and bacteremia with pathogens carried in the airway. Streptococcal and staphylococcal infections are more likely to occur through secondary infection of vesicles but they can also invade from the upper airway. Bacterial exotoxins may contribute to injury, as exemplified by the case of staphylococcal scalded skin syndrome and the two cases of streptococcal infection. The Canadian Paediatric Society Surveillance Program identified varicella as the predisposing factor in 16 of 26 cases (61%) of necrotizing fasciitis caused by group A streptococci, emphasizing the common association of streptococcal and varicella infections (3
The viremic phase of chickenpox ordinarily distributes virus to the skin without causing injury to other tissues. With high-grade viremia, visceral lesions can develop, most commonly in the lungs and liver. Three children in this series died of varicella pneumonitis, one of whom also had multiorgan injury. The hallmark of varicella pneumonitis is bilateral nodular lung infiltrates on radiological examination of the chest. All three children with pneumonitis had such lung infiltrates.
It is jarring to speak of deaths in relation to a common childhood infection like chickenpox. The complete Canada-wide varicella case fatality count from 2000 to 2005 is not yet available but likely exceeds the seven cases summarized in the present report. In the United States (US), six of the eight varicella-related deaths reported in 2003 and early 2004 involved children (4
). Routine vaccination in the US is substantially reducing varicella hospital admissions and deaths. By 2001, the US hospitalization rate for varicella among young children had declined 84% from prevaccine rates (5
). With improving VZ vaccination rates, the situation will approach that of measles, which was once as common as varicella but has not caused a death in Canada in the past decade and only rarely causes hospital admissions. Deaths from other former childhood killers such as tetanus, diphtheria and polio have ceased to occur as a result of widespread immunization. Deaths from varicella should be equally intolerable given a safe alternative.
Some physicians have been slow to accept VZ vaccine for a variety of reasons. For those who consider chickenpox a benign illness, we have described seven reasons to reconsider that view. With rapidly advancing bacterial or viral complications, antimicrobial treatment may not be sufficient to avoid unfortunate outcomes, even with intensive care. Prevention through vaccination is the better approach.
Earlier questions about some of the properties of the VZ vaccine have been extensively addressed:
- The vaccine has an excellent safety record, even when given concurrently with measles, mumps and rubella (MMR) vaccination.
- Protection is long-lasting, spanning decades (6).
- Infections that occur despite vaccination are generally mild, with an average of only 20 spots (6).
- Vaccinated persons have a substantially reduced risk of zoster, which occurs in a mild form with minimal neuralgia.
- Concern that reducing VZ virus circulation among vaccinated children may lead to more zoster in adults (for lack of subclinical reinfections to boost protection) has not been supported by evidence to date in highly vaccinated US communities (7).
- Vaccines combining MMR and VZ vaccines will soon be licensed, avoiding the inconvenience of separate injections. Availability of a combined vaccine will favour two-dose schedules, which have the potential to elicit more complete and durable protection.
In short, the benefits of VZ vaccination substantially outweigh the risks and remaining unknowns attached to it. The Canadian Paediatric Society recommends routine VZ vaccination (8
), which is in agreement with national guidelines and has the full support of the authors.