Breakthrough infection

A breakthrough infection is a case of illness in which a vaccinated individual becomes sick from the same illness that the vaccine is meant to prevent. Simply, they occur when vaccines fail to provide immunity against the pathogen they are designed to target. Breakthrough infections have been identified in individuals immunized against a variety of different diseases including Mumps, Varicella (Chicken Pox), and Influenza. The character of breakthrough infections is dependent on the virus itself. Often, the infection in the vaccinated individual results in milder symptoms and is of a shorter duration than if the infection was contracted naturally. A breakthrough infection is a case of illness in which a vaccinated individual becomes sick from the same illness that the vaccine is meant to prevent. Simply, they occur when vaccines fail to provide immunity against the pathogen they are designed to target. Breakthrough infections have been identified in individuals immunized against a variety of different diseases including Mumps, Varicella (Chicken Pox), and Influenza. The character of breakthrough infections is dependent on the virus itself. Often, the infection in the vaccinated individual results in milder symptoms and is of a shorter duration than if the infection was contracted naturally. Causes of breakthrough infections include improper administration or storage of vaccines, mutations in viruses and antibody blocking. For these reasons, vaccines are rarely 100% effective. The common flu vaccine is estimated to provide immunity to the flu in 58% of recipients. The measles vaccine fails to provide immunity to 2% of children that receive the vaccine. However, if herd immunity exists, it typically prevents individuals who are ineffectively vaccinated from contracting the disease. Accordingly, herd immunity reduces the number of breakthrough infections in a population. The varicella vaccine is 85% effective at preventing varicella infection. However, 75% of individuals that are diagnosed with breakthrough varicella exhibit milder symptoms than individuals that are not vaccinated. These individuals with mild varicella have low fevers, fewer than 50 lesions on their skin and a maculopapular rashes. In contrast, unvaccinated individuals typically have a fever of 102, 200-500 skin lesions and macules (lesions that are not elevated) evolve to papules and vesicular lesions. Additionally, infection in unvaccinated individuals tends to last for a longer period of time than in individuals who have been infected. The majority of cases of breakthrough varicella are attributed to the failure of an individual to uptake the varicella vaccine. Therefore, to prevent breakthrough infections, it is proposed that children receive a second dose of varicella vaccine less than a year after getting their first dose. The mumps vaccine is a component of the Measles, Mumps and Rubella vaccine (MMR). The mumps vaccine, specifically, is 88% effective at preventing mumps. Individuals with breakthrough cases of mumps have fewer serious complications from the infections as compared to individuals unvaccinated for mumps. These complications include the development of aseptic meningitis and encephalitis. The cause of breakthrough mumps is not currently completely understood. Evolution of the virus (antigenic drift) is thought to explain the majority of breakthrough cases. Other theories suggest that memory T lymphocytes play a role in the development of breakthrough infections. Breakthrough cases of Hepatitis B are primarily attributed to mutations in the Hepatitis B virus (HBV) that make HBV surface proteins unrecognizable to antibodies produced from the HBV vaccine. Viruses with such mutations are called “vaccine escape mutants”. Breakthrough infections may also be caused by delayed vaccination, immunosuppression, and maternal viral load. It is possible for an individual to have breakthrough infection of HBV but be asymptomatic. As a person ages, their immune system undergoes a series of changes, in a process referred to as immunosenescence. Notable among these changes is a decreased production of naive T cells and naive B cells. The reduced number of naive lymphocytes (T and B cells) is attributed to the fact that the telomeres in hematopoietic stem cells (HSCs), degenerate over time and, consequently, limit the proliferation of HSCs and production of lymphoid progenitor cells. This is compounded by the fact that, with time, HSCs tend to favor the production of myeloid progenitor cells over lymphoid progenitor cells. Mature lymphocytes are also unable to proliferate indefinitely. Compounded, the reduction in number of naive lymphocytes and limitations of the proliferative abilities of mature lymphocytes contribute to a limited number and variety of lymphocytes to respond to pathogens presented in a vaccine. Indeed, vaccines, including the influenza vaccine, Tdap, and pneumococcal vaccines, are less effective in adults over the age of 65. Nevertheless, the CDC recommends that elderly adults get the flu vaccine because influenza infection is particularly dangerous in this population and vaccine provides at least a moderate level of immunity to the flu virus.