Claire Thompson
Chickenpox, or varicella, is a highly contagious disease caused by the varicella-zoster virus (VZV). Since the introduction of the chickenpox vaccine in the United States in 1995, cases of chickenpox have declined by more than 97%, making it a rare disease in the country. However, there have been reports of vaccine failure, where vaccinated individuals still contract chickenpox. This can be classified as primary vaccine failure, which is the failure to mount a protective immune response after vaccination, or secondary vaccine failure, which is the gradual loss of immunity over time. While the effectiveness of the vaccine is usually around 85%, rates as low as 44% have been observed, and breakthrough varicella rates in some outbreaks have been as high as 42%. Several factors have been proposed to increase the risk of vaccine failure, including immunization at a young age and the time since vaccination.
| Characteristics | Values |
|---|---|
| Effectiveness of 1-dose varicella vaccination | ~85% |
| Range of effectiveness of 1-dose varicella vaccination in published outbreaks | 20% to 100% |
| Effectiveness of 1-dose varicella vaccination for moderate/severe disease | 85.5% to 100% |
| Range of breakthrough varicella rates | 0% to 42% |
| VZV seroconversion rate determined with FAMA assay | 76% |
| VZV seroconversion rate determined with gpELISA assay | >95% |
| Total effectiveness rate of varicella vaccine | ~90% |
| Reduction in chickenpox cases in the U.S. since the start of the vaccination program in 1995 | >97% |
| Reduction in chickenpox cases between 1995 and 2004 | 85% |
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What You'll Learn
- Chickenpox cases have declined by 97% since the US immunization program began in 1995
- Breakthrough varicella is caused by primary or secondary vaccine failure
- Primary vaccine failure is when there is a failure to mount a protective immune response
- Secondary vaccine failure is the gradual loss of immunity over time
- Risk factors for vaccine failure include immunization at a young age and time since vaccination
Chickenpox cases have declined by 97% since the US immunization program began in 1995
Primary vaccine failure is defined as the failure to seroconvert or the failure to mount a protective immune response after vaccination despite seroconversion. In a study of 148 healthy children vaccinated against varicella, 76% seroconverted, while 24% had no detectable VZV FAMA antibodies. This is a significantly lower seroconversion rate than that obtained with the gpELISA assay, which is commonly used due to its ease of use and automation. The high gpELISA-determined seroconversion rates do not correspond well with the demonstrated effectiveness of the varicella vaccine, which is 80%–85%.
Breakthrough varicella is defined as the appearance of a pruritic maculopapulovesicular rash with onset >42 days after vaccination without any other apparent cause. While it is generally milder than natural varicella, it is still a cause for concern due to the risk of VZV transmission from the rash. Several countries have implemented recommendations for a 2-dose varicella vaccination schedule to address breakthrough varicella. A second dose of the vaccine is expected to increase seroconversion rates and vaccine effectiveness.
The success of the US chickenpox vaccination program has been highlighted in a special supplement in the Journal of Infectious Diseases. During the first 25 years of the program, it prevented an estimated 91 million cases of chickenpox and saved $23.4 billion in healthcare costs. Chickenpox is now rare in the United States, and the vaccine has helped protect vulnerable individuals who could not receive the vaccine, including those who are immunocompromised, pregnant, or too young. The vaccine has also had economic benefits, saving an estimated $23 billion in medical costs and lost wages due to parents staying home with sick children.
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Breakthrough varicella is caused by primary or secondary vaccine failure
Chickenpox, or varicella, is a highly contagious disease caused by the varicella-zoster virus (VZV). In 1995, the United States became the first country to include the chickenpox vaccine as part of its routine childhood immunization schedule. Since then, several other countries have followed suit, resulting in substantial reductions in the number of varicella cases, hospitalizations, and deaths worldwide.
Despite the success of chickenpox vaccination programs, breakthrough varicella infections can still occur in vaccinated individuals. Breakthrough varicella is defined as the appearance of a pruritic maculopapulovesicular rash with onset >42 days after vaccination, without any other apparent cause. While milder than natural varicella, breakthrough varicella is still a concern due to the risk of VZV transmission and the potential to establish latency, leading to herpes zoster.
On the other hand, secondary vaccine failure refers to the gradual waning of immunity over time. Even if an individual initially develops a protective immune response after vaccination, their immunity may decrease years later, leaving them susceptible to breakthrough varicella infections. The optimal timing of the second vaccine dose depends on whether breakthrough varicella is primarily due to primary or secondary vaccine failure.
Studies have shown that a single dose of the varicella vaccine is only about 85% effective in preventing the disease, and rates as low as 44% have been observed. While the second dose of the vaccine has been shown to increase effectiveness to 98%, the optimal timing between the two doses is still unknown. However, given the high rate of primary vaccine failure, a shorter interval between doses is generally recommended to prevent breakthrough infections and potential epidemics in vaccinated but unprotected adults.
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Primary vaccine failure is when there is a failure to mount a protective immune response
Chickenpox vaccines have been part of the routine childhood immunization schedule in the United States since 1995, and they have significantly decreased the incidence of chickenpox. The program has been highly effective, reducing chickenpox cases by over 97% and saving billions in healthcare costs.
However, there have been reports of vaccine failure and breakthrough varicella (chickenpox) infections among vaccinated individuals. Primary vaccine failure is defined as the failure to mount a protective immune response after vaccination. In other words, it is when an individual does not develop immunity against the virus even after receiving the vaccine.
Several studies have investigated primary vaccine failure after 1 dose of the varicella vaccine. One study found that out of 148 healthy children vaccinated, 24% showed no detectable antibodies against the varicella-zoster virus (VZV), indicating a primary vaccine failure rate of 24%. Another study reviewed literature on vaccine failure and identified 21 varicella outbreaks with breakthrough varicella rates ranging from 0% to 42%.
Risk factors associated with increased varicella vaccine failure include young age at immunization (below 12-15 months), time since vaccination with other live virus vaccines, history of eczema, asthma, vaccine brand, and the use of corticosteroids.
To address primary vaccine failure and improve protection, several countries have recommended a 2-dose varicella vaccination schedule. A second dose is expected to increase seroconversion rates and improve vaccine effectiveness.
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Secondary vaccine failure is the gradual loss of immunity over time
Chickenpox vaccines have been highly effective in reducing the number of cases, hospitalizations, and deaths. Since the start of the U.S. vaccination program in 1995, cases have declined by more than 97%, proving the vaccine's effectiveness as a public health intervention.
However, breakthrough varicella (chickenpox) cases still occur in vaccinated individuals, and this is often attributed to primary or secondary vaccine failure. Secondary vaccine failure refers to the gradual loss of immunity over time. While the exact duration of protection from the varicella vaccine is unknown, studies have shown that vaccinated individuals maintain antibodies for at least 10 to 20 years.
Published literature has indicated a relatively high rate of primary vaccine failure and limited evidence of secondary vaccine failure among 1-dose varicella vaccine recipients. Breakthrough varicella rates ranged from 0% to 42%, with no consistent trend between the rate and time since vaccination. However, it is important to note that the effectiveness of the vaccine is influenced by the rate of vaccination in the community.
The distinction between primary and secondary vaccine failure is crucial. Primary vaccine failure occurs when an individual fails to develop a protective immune response after vaccination, despite seroconversion. In contrast, secondary vaccine failure involves the waning of immunity over time, leading to breakthrough varicella infections.
To address secondary vaccine failure and improve protection, several countries have implemented a 2-dose varicella vaccination schedule. The second dose is typically administered between the ages of 4 and 6 years, but providing it earlier may offer enhanced protection. The 2-dose schedule aims to boost immunity and prevent breakthrough infections, particularly in older children and adults, where the risk of complications is higher.
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Risk factors for vaccine failure include immunization at a young age and time since vaccination
Chickenpox vaccines have been highly effective in reducing the number of cases, hospitalizations, and deaths. Since the start of the U.S. vaccination program in 1995, cases have declined by more than 97%, proving the vaccine's effectiveness as a public health intervention. The program has prevented an estimated 91 million cases and saved billions in healthcare costs.
However, vaccine failure can occur, and breakthrough varicella (chickenpox) cases have been reported. Primary vaccine failure refers to the inability to mount a protective immune response after vaccination, while secondary vaccine failure is the gradual waning of immunity over time. Risk factors for vaccine failure include immunization at a young age and time since vaccination.
Young children who receive the vaccine may experience primary vaccine failure due to the presence of maternal antibodies or subclinical varicella, resulting in false-positive results and overestimations of VZV seroconversion rates. The effectiveness of the vaccine also decreases with time since vaccination. Children between 8 and 12 years old vaccinated five or more years ago were twice as likely to experience moderate-to-severe breakthrough disease compared to those vaccinated less than five years ago.
To mitigate these risks, a two-dose varicella vaccination schedule is recommended. The second dose, administered between ages 4 to 6 years, provides additional protection and increases seroconversion rates. The effectiveness of the vaccine is also dependent on community vaccination rates, as higher rates provide better protection for the entire community.
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Frequently asked questions
Chickenpox vaccines have been part of the routine childhood immunization schedule in the United States since 1995. The vaccine has significantly decreased the incidence of chickenpox, reducing cases by 97% overall.
The failure rate of the chickenpox vaccine is unclear, but it is suggested that many cases of chickenpox in immunized children are due to primary vaccine failure. Vaccine effectiveness has usually been around 85%, but rates as low as 44% have been observed.
Primary vaccine failure is defined as the failure to mount a protective immune response after a dose of the vaccine. A study of 148 healthy children who received the vaccine found that 24% had no detectable antibodies against the virus.
Breakthrough varicella is the appearance of a rash more than 42 days after vaccination without any other apparent cause. It is caused by primary or secondary vaccine failure and can lead to the transmission of the varicella zoster virus.
