Sarah Bennett
The varicella vaccine has been widely successful in reducing the number of hospitalizations and deaths due to chickenpox. However, there have been some reported cases of vaccinated individuals still contracting the disease. While the vaccine is highly effective in preventing chickenpox, it is not known how long immunity lasts, and there may be a decline in effectiveness over time. Several factors, such as the time since vaccination and the need for community exposure to boost immunity, could play a role in breakthrough varicella cases. This article will explore the latest research on vaccine-induced immunity to varicella and discuss the potential reasons why some vaccinated individuals may still be susceptible to the disease.
| Characteristics | Values |
|---|---|
| Lack of immunity after vaccination | Unclear whether vaccine-induced immunity wanes over time, but studies show antibodies present for at least 10-20 years |
| Breakthrough varicella | Increased risk of moderate-to-severe disease in children vaccinated more than 5 years ago; outbreaks reported in highly vaccinated school communities |
| Vaccine effectiveness | 97% effective in the first year, 86% in the second year, and 81-86% from the second to eighth year; two doses improve protection with a pooled estimate of 92% |
| Contraindications | Not suitable for people with impaired humoral immunity and HIV infection |
| Assessing immunity | Commercial assays lack sensitivity to detect vaccine-induced immunity; evidence of immunity includes documentation of age-appropriate vaccination or verification of a history of varicella by a healthcare provider |
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What You'll Learn
- The effectiveness of one dose of the varicella vaccine
- The impact of time since vaccination on breakthrough varicella risk
- The importance of a second dose of the varicella vaccine
- The limitations of commercial assays in detecting vaccine-induced immunity
- The contraindications for the varicella vaccine in certain individuals
The effectiveness of one dose of the varicella vaccine
The varicella vaccine is highly effective in preventing confirmed cases of varicella, although its effectiveness declines over time. The vaccine's effectiveness was evaluated in a case-control study in Navarre, Spain, in 2010–2012, which found that a single dose was 87% effective. Another case-control study conducted from 1997 to 2003 showed that one dose of the vaccine was 97% effective in the first year after vaccination and 86% effective in the second year. From the second to the eighth year after vaccination, the vaccine's effectiveness remained stable, ranging from 81% to 86%.
However, the risk of breakthrough varicella increases over time, and the effectiveness of the vaccine wanes. The introduction of universal varicella vaccination in 1995 substantially reduced varicella-related morbidity and mortality, but outbreaks continue to occur, especially in highly vaccinated school communities. This has led to the recommendation of a second dose to boost immunity and protect against vaccine failure.
Two doses of the varicella vaccine are recommended for children, adolescents, and adults who do not have evidence of immunity. The second dose helps to re-establish high levels of effectiveness and reduce the risk of breakthrough varicella. While the first dose provides good short-term protection, the second dose achieves higher antibody titers, suggesting greater and longer-lasting protection.
It is important to note that the effectiveness of the vaccine may vary depending on individual factors, and there is a possibility of vaccine failure even with two doses. The median time since vaccination is also a factor to consider, as the protection offered by the vaccine may decline after a certain period.
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The impact of time since vaccination on breakthrough varicella risk
The varicella vaccine has significantly reduced varicella-related morbidity and mortality, especially in the United States. However, there is still a chance of contracting the disease even after being vaccinated. This occurrence is known as "breakthrough varicella".
Several studies have been conducted to examine the impact of time since vaccination on the risk of breakthrough varicella. One study analysed 10 years of active surveillance data from 1995 to 2004, with a total of 350,000 subjects. The results showed that 9.5% of the subjects experienced breakthrough disease, and the annual rate of breakthrough varicella increased with time since vaccination. Specifically, the rate increased from 1.6 cases per 1000 person-years within the first year of vaccination to 9.0 cases per 1000 person-years at 5 years, and 58.2 cases per 1000 person-years at 9 years.
Another study conducted in 2012 analysed 45 cases and 135 controls and found that the time between vaccination and virus exposure was longer among cases. Logistic regression analysis revealed that the duration of time from vaccination was a significant factor associated with breakthrough disease.
The results of these studies suggest that the risk of breakthrough varicella increases with the time elapsed since vaccination. However, it is important to note that other factors, such as age, calendar year, and exposure to the virus, may also influence the risk of breakthrough disease.
Furthermore, it is recommended that individuals receive two doses of the varicella vaccine, as this has been shown to provide improved protection against breakthrough varicella compared to a single dose. The CDC recommends two doses of the vaccine for children, adolescents, and adults who do not have evidence of immunity. The two licensed vaccines in the United States are the single-antigen varicella vaccine (Varivax) and the measles, mumps, rubella, and varicella (MMRV) vaccine (ProQuad).
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The importance of a second dose of the varicella vaccine
The varicella vaccine, which protects against chickenpox, is recommended by the CDC as a two-dose series of shots for children, adolescents, and adults who do not have evidence of immunity. The first dose is typically given when a child is between 12 and 15 months old, and the second dose is administered when the child is between 4 and 6 years old. For adolescents and adults over 13 years of age, the two doses should be administered at least 28 days apart.
The two-dose vaccine is about 90% effective at preventing chickenpox. While the first dose is highly effective at preventing infection in the first two years, its effectiveness decreases slightly in subsequent years. A clinical trial showed that the two-dose vaccine provided protection for up to 10 years after vaccination, with fewer cases of breakthrough varicella compared to the one-dose vaccine. This is supported by another study that found that two doses of the vaccine provided improved protection, with a 92% effectiveness rate approximately five years after vaccination.
The importance of the second dose is further emphasized by the potential loss of vaccine-induced immunity over time. While the introduction of the varicella vaccine has significantly reduced morbidity and mortality associated with the disease, there have been outbreaks of varicella in highly vaccinated communities, suggesting that the time since vaccination may play a role in the risk of breakthrough infections.
Therefore, it is recommended that individuals who have only received one dose of the varicella vaccine should get a second dose at the appropriate time interval to ensure optimal protection against the disease.
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The limitations of commercial assays in detecting vaccine-induced immunity
Commercial assays can be used to assess disease-induced immunity, but they often lack the sensitivity to detect vaccine-induced immunity. This means that they may yield false-negative results, indicating that a person is not immune to a disease after vaccination when they actually are. This limitation can have important implications for public health and individual decision-making.
For example, in the context of varicella (chickenpox) vaccination, commercial assays may not accurately detect vaccine-induced immunity. The CDC recommends two doses of the varicella vaccine for individuals without evidence of immunity, and this recommendation is based on the assumption that the vaccine effectively prevents infection. However, some individuals may still be susceptible to varicella even after receiving the vaccine.
Breakthrough cases of varicella have been observed in vaccinated individuals, and the risk of these cases may increase over time since vaccination. This suggests that vaccine-induced immunity against varicella may wane over time, leaving individuals susceptible to infection later in life when the risk of serious complications is greater. The limitations of commercial assays in detecting vaccine-induced immunity can impact our understanding of the durability of protection offered by the varicella vaccine.
To address this challenge, researchers have optimized and validated serological assays, such as anti-ORF8 and anti-N C-terminal domain (NCTD) ELISA assays, to differentiate between natural infection and vaccine-induced immunity. These assays have shown good discrimination between natural COVID-19 infection and vaccination in individuals who received the BNT162b2 vaccine but less discrimination in those who received the CoronaVac vaccine.
The development of high-sensitivity immunogenicity assays, such as those with ultrasensitive Single Molecule Counting (SMC®) technology, is also improving the detection of immune responses to vaccines. These assays can speed up the development of ADA assays and enable the detection of immune responses that were previously challenging to identify. By enhancing our ability to detect and analyze ADA formation, these assays play a crucial role in therapeutic protein product development and our understanding of vaccine-induced immunity.
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The contraindications for the varicella vaccine in certain individuals
The varicella vaccine has been highly successful in reducing varicella-related morbidity, mortality, and healthcare costs. However, certain individuals may not be suitable candidates for the vaccine due to specific contraindications.
Firstly, individuals with impaired humoral immunity, including conditions such as hypogammaglobulinemia and dysgammaglobulinemia, are contraindicated for the MMRV vaccine. Additionally, the MMRV vaccine is not recommended for individuals with HIV infection. In such cases, alternative options like varicella-zoster immune globulin may be considered after exposure to varicella or herpes zoster.
Moreover, individuals with a history of serious allergic reactions, such as anaphylaxis, to a previous dose of the varicella vaccine or its components should avoid subsequent doses. This precaution is essential to prevent further adverse reactions.
The CDC also provides specific guidelines for immunocompromised individuals. They recommend the varicella vaccination for children with humoral immunodeficiencies, but not cellular immunodeficiencies. Additionally, they outline specific criteria for HIV-infected children considering the varicella vaccine, taking into account factors like age, CD4+ T-lymphocyte percentages or counts, and the duration of stability.
It is important to note that evidence of immunity also plays a role in vaccination recommendations. Individuals with documentation of age-appropriate varicella vaccination or laboratory confirmation of immunity may not require revaccination. Furthermore, birth in the United States before 1980 is not considered sufficient evidence of immunity for healthcare personnel, pregnant women, and immunocompromised individuals.
In summary, while the varicella vaccine is generally safe and effective, certain contraindications must be considered to ensure the safety of specific individuals. These contraindications include impaired humoral immunity, HIV infection, history of serious allergic reactions, and specific guidelines for immunocompromised individuals.
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Frequently asked questions
It is recommended that two doses of the varicella vaccine be administered, and a person is considered fully vaccinated when they have received both doses. The effectiveness of the vaccine is estimated to be 81% to 86% from the second year after vaccination to the eighth year. However, it is unclear how long a person remains protected after that. Several factors, such as age at vaccination and calendar year, may influence the duration of immunity.
The time since vaccination may influence the risk of breakthrough varicella. Studies have shown that vaccinated individuals maintained antibodies for at least 10 to 20 years, but these studies were conducted before widespread vaccine use. More recent data suggests that the effectiveness of one dose of the vaccine is around 82% within the first decade, with a slight decline in effectiveness over time.
The CDC recommends two doses of the varicella vaccine, with each dose administered subcutaneously and separated by at least three months. The second dose should be given at least 28 days after the first dose. Receiving both doses will provide improved protection against varicella.
