Chickenpox, a highly contagious illness caused by the varicella-zoster virus, was once a common childhood experience, characterized by an itchy, blister-like rash. Before the introduction of the varicella vaccine in 1995, almost every child would contract the disease. While vaccination has significantly reduced the incidence of chickenpox, many parents wonder if their vaccinated child can still get the illness.
Yes, It’s Possible
A child who has received the chickenpox vaccine can still develop the illness, a phenomenon known as a “breakthrough infection.” This occurs when a vaccinated individual contracts the varicella-zoster virus despite having been immunized. Although it is possible, breakthrough chickenpox is generally less common than the illness in unvaccinated individuals. When it does occur, the experience is typically much milder.
Breakthrough infections are rare, affecting less than 10% of vaccinated children. The possibility of a breakthrough case highlights that while vaccines offer strong protection, no vaccine provides 100% immunity for every individual.
Understanding Vaccine Effectiveness
No vaccine offers absolute protection for every recipient. Vaccine effectiveness refers to how well a vaccine performs in real-world settings. For the varicella vaccine, two doses are recommended for optimal protection.
A single dose of the varicella vaccine is estimated to be about 82% effective at preventing any form of chickenpox. However, this effectiveness can decline over time. Two doses of the varicella vaccine significantly enhance protection. Clinical trials and post-licensure studies show that two doses are approximately 92% to 98% effective at preventing all forms of chickenpox. The second dose helps to reestablish very high levels of effectiveness and reduces the risk of breakthrough varicella.
Individual immune responses also play a role in vaccine effectiveness. Some individuals may not mount as robust an immune response to the vaccine as others, which can influence their level of protection. Even with two doses, a small percentage of vaccinated children may still be susceptible to the virus.
What a Breakthrough Case Looks Like
When a vaccinated child develops chickenpox, the illness usually presents differently than in an unvaccinated person. Breakthrough cases are much milder, with a reduced number of lesions and less severe symptoms. This is because the vaccine provides a level of partial immunity that helps the body fight off the virus more effectively.
A vaccinated child with breakthrough chickenpox might have fewer than 50 lesions, often appearing as red spots rather than the classic fluid-filled blisters. These lesions may be more maculopapular, flat or slightly raised, with few or no vesicles. In contrast, unvaccinated individuals can develop 250 to 500 lesions.
Children with breakthrough chickenpox often experience no fever or only a low-grade fever, unlike the higher fevers common in unvaccinated cases. The illness also tends to be shorter in duration, lasting 1 to 4 days, compared to 5 to 7 days for unvaccinated individuals. While the rash can still be itchy, the discomfort is usually less pronounced.
Caring for a Child with Breakthrough Chickenpox
Even with a milder presentation, caring for a child with breakthrough chickenpox involves managing symptoms and preventing further spread. For fever and discomfort, acetaminophen can be given. It is important to avoid giving aspirin to children with chickenpox due to the risk of Reye’s syndrome, a serious illness.
To alleviate the itching, cool baths with colloidal oatmeal or baking soda can provide relief. Calamine lotion or other fragrance-free, anti-itch lotions can also be applied to the rash. Keeping fingernails trimmed short and covering hands with mittens or socks, especially at night, can help prevent scratching and potential skin infections.
Despite the mildness of breakthrough cases, the virus is still contagious. A vaccinated person with breakthrough chickenpox can still spread the virus, though those with fewer than 50 lesions may be about one-third as contagious as unvaccinated individuals. Children should be kept home from school or childcare until no new lesions have appeared for at least 24 hours. For lesions that do not crust, isolation continues until the rash has faded and no new spots have developed within a 24-hour period. Seek medical attention if the rash becomes red, painful, or oozes pus, if the fever is high, or if the child experiences severe headache, vomiting, or difficulty breathing.