Varicella vaccine
Encyclopedia
The varicella vaccine is a live (attenuated) virus that protects against the viral disease commonly known as chickenpox
caused by Varicella Zoster Virus
(VZV). Varicella vaccine is marketed as Varivax in the U.S. by Merck
. Another vaccine that is known as Zostavax
and used to reduce the risk of shingles (also called Herpes zoster
) and Postherpetic neuralgia
is caused by the same virus, Varicella Zoster Virus
(VZV), and is simply a larger-than-normal dose of Varivax.
During 2003 and the first half of 2004, the CDC reported eight deaths from varicella, six of whom were children or adolescents. These deaths and hospitalizations have substantially declined in the U.S. due to vaccination, though the rate of shingles infection has increased for the same reason. Ten years after the vaccine was recommended in the U.S., the CDC reported as much as a 90% drop in chicken pox cases, a varicella-related hospitalization decline of 71% and a 97% drop in chicken pox deaths among those under 20. In 2006, the shingles vaccine was determined to be effective at preventing shingles (zoster) in persons 60 years of age and older, if administered regularly. In 2011, the FDA approved Zostavax for those 50 to 59 years old.
, and the incidence of chickenpox has been dramatically reduced there (from 4 million cases per year in the pre-vaccine era to approximately 400,000 cases per year as of 2005). In Europe
most countries do not currently vaccinate against varicella, though the vaccine is gaining wider acceptance. Australia, Canada, and other countries have now adopted recommendations for routine immunization of children and susceptible adults against chickenpox.
Vaccination is common in the United States, with 41 of the 50 states require immunization for children attending government-run schools. All 50 states offer a medical exemption, with 48 of those states also offering philosophical and/or religious exemptions. The vaccination is not routine in the United Kingdom. In the U.S. opinions that it should be dropped (individually or along with all immunizations) are also sometimes voiced.
Other countries, such as Germany
and the United Kingdom
, have targeted recommendations for the vaccine, e.g., for susceptible health care workers at risk of varicella exposure. In the UK, varicella antibodies are measured as part of the routine of prenatal care, and by 2005 all National Health Service
personnel had determined their immunity and been immunized if they were non-immune and have direct patient contact. Population-based immunization against varicella is not otherwise practiced in the UK. It is feared that there would be a greater number of cases of shingles in adults, until the vaccination was given to the entire population—because adults who have had chickenpox as a child are less likely to have shingles in later life if they have been exposed occasionally to the chickenpox virus (for example by their children). This is because the exposure acts as a booster vaccine.
The long-term duration of protection from varicella vaccine is unknown, but there are now persons vaccinated more than thirty years ago with no evidence of waning immunity, while others have become vulnerable in as few as 6 years. Assessments of duration of immunity are complicated in an environment where natural disease is still common, which typically leads to an overestimation of effectiveness, and we are only now entering an era in the U.S. where the long-term efficacy of varicella vaccine can be accurately gauged.
The vaccine is exceedingly safe: approximately 5% of children who receive the vaccine develop a fever or rash, but as of 1 May 2006, there have been no deaths yet attributable to the vaccine despite more than 40 million doses being administered.
Cases of vaccine-related chickenpox have been reported in patients with a weakened immune system, but no deaths.
The literature contains several reports of adverse reactions following varicella vaccination, including vaccine-strain zoster in children and adults.
A mean of 2,350 reports per year are attributed to varicella vaccine based on 20,004 cases reported to the Vaccine Adverse Event Reporting System (VAERS) database from May, 1995 through December, 2003. Minor events are known to be under-reported to VAERS.
Two doses are always recommended. In the first case a first dose is administered at 12 to 15 months and a second dose at age 4-6 years. For people older than 13 the two doses are administered 4 to 8 weeks apart.
The varicella vaccine is not recommended for seriously ill people, pregnant women, people who have experienced a serious allergic reaction to the varicella vaccine in the past, people who are allergic to gelatin
, people allergic to neomycin
, people suffering from an immune system disease, such as HIV
, people receiving high doses of steroids, people receiving treatment for cancer
with x-rays, drugs
or chemotherapy
, as well as people who have received blood products or transfusions during the past 5 months.
, pneumonia
, and anaphylaxis
.
The possible mild side effects include redness, stiffness
, and soreness at the injection site, as well as fever
. A few people may develop a mild rash
which usually appears around the shot's area.
There is a risk of developing herpes zoster
(shingles) following vaccination. However, this risk is less than the risk due to a natural infection resulting in chickenpox. Most of the cases reported have been mild and have not been associated with serious complications.
, clinical trials have demonstrated that varicella vaccine is 70% to 90% effective for preventing varicella and more than 95% effective for preventing severe varicella.
Furthermore, follow-up evaluations took place in the United States of children immunized that revealed protection for at least 11 years. Also, studies were conducted in Japan
which indicated protection for at least 20 years.
People who do not develop enough protection when they get the vaccine may develop a mild case of the disease when in close contact with a person with chickenpox. In these cases, people show very little sign of illness. This has been the case of children who get the vaccine in their early childhood
and later have contact with children with chickenpox. Some of these children may develop a mild chickenpox also known as breakthrough disease.
Zoster (shingles) most often occurs in the elderly. Multiple studies have not observed any effect on zoster incidence. This may be because infants and children immunized in varicella vaccination programs have not yet reached the age where zoster typically occurs. It is likewise too early to observe the effect on postherpetic neuralgia
(PHN).
It has been claimed that adult shingles may increase after introduction of varicella vaccine.
Preliminary evidence that this has occurred is available from data collected from the Antelope Valley Varicella Surveillance Project (VASP) which began surveillance of shingles in 2000. VASP case reports indicate there was a statistically significant increase in adult shingles cases reported to the Antelope Valley Varicella Active Surviellance Project (VASP) from 2000 to 2003. The 56.1% increase from 237 cases in 2000 to 370 cases in 2002 yields a rate ratio of 1.4 (95% C.I. 1.2-1.7). Increases in cases of shingles reported to VASP occurred in every age category (except 70+) from 2000 to 2001. VASP also reported that verified cases of shingles among adults aged 50 years and older increased 27.5% from 2006 to 2007. (Annual Summary, 2001, 2002, 2003, 2006, 2007 Antelope Valley Varicella Active Surveillance Project, Los Angeles County Department of Health Services; Centers for Disease Control and Prevention (CDC) Cooperative Agreement No. U66/CCU911165-10; Mascola L, et al.)
Additional controversy has arisen because cell lines derived from aborted fetal tissue were used in its development, and thus violates the ethics and beliefs of people who oppose the use of aborted fetal tissue in medical research.
: "After observation of study populations for periods of up to 20 years in Japan and 10 years in the United States, more than 90% of immunocompetent persons who were vaccinated as children were still protected from varicella." However, since only one out of five Japanese children were vaccinated, the annual exposure of these vaccinees to children with natural chickenpox boosted the vaccinees' immune system. In the United States, where universal varicella vaccination has been practiced, the majority of children no longer receive exogenous (outside) boosting, thus, their cell-mediated immunity to VZV (varicella zoster virus) wanes--necessitating booster chickenpox vaccinations.
Some persons exposed to the virus after vaccine can experience milder cases of chicken pox (and usually then harbor both the attenuated vaccine or oka strain as well as the wild type or natural chickenpox strain which are both subject to reactivation as shingles).
Catching "wild" chickenpox as a child has been thought to commonly result in lifelong immunity. Indeed, parents have deliberately ensured this in the past with "pox parties" (see below). Historically, exposure of adults to contagious children has boosted their immunity, reducing the risk of shingles.
The CDC and corresponding national organisations are carefully observing the failure rate which may be high compared with other modern vaccines - large outbreaks of chickenpox having occurred at schools which required their children to be vaccinated.
. Vaccines are less effective among these high-risk patients, as well as being more dangerous because they contain attenuated live virus (see last footnote). In a study performed on children with an impaired immune system
, 30% had lost the antibody after five years, and 8% had already caught wild chickenpox in that five year period.
, but are now discouraged by doctors and health services due to the risk of serious injury or death (even in children, as described above) from acquiring the disease. The reasoning behind such parties is that guests exposed to the varicella virus will contract the disease and develop strong and persistent immunity
at an age before disaster is likely, particularly from chickenpox or rubella
. The first reference to such a practice is the letter of Lady Montagu to Sarah Chiswell describing parties held in Istanbul for the purpose of variolation—an effective technique for gaining immunity to smallpox
. Lady Montagu imported variolation to England.
Chickenpox
Chickenpox or chicken pox is a highly contagious illness caused by primary infection with varicella zoster virus . It usually starts with vesicular skin rash mainly on the body and head rather than at the periphery and becomes itchy, raw pockmarks, which mostly heal without scarring...
caused by Varicella Zoster Virus
Varicella zoster virus
Varicella zoster virus is one of eight herpes viruses known to infect humans . It commonly causes chicken-pox in children and Herpes zoster in adults and rarely in children.-Nomenclature:...
(VZV). Varicella vaccine is marketed as Varivax in the U.S. by Merck
Merck & Co.
Merck & Co., Inc. , also known as Merck Sharp & Dohme or MSD outside the United States and Canada, is one of the largest pharmaceutical companies in the world. The Merck headquarters is located in Whitehouse Station, New Jersey, an unincorporated area in Readington Township...
. Another vaccine that is known as Zostavax
Zostavax
Zostavax is a live vaccine developed by Merck & Co. which has been shown to reduce the incidence of herpes zoster by 51.3% in a study of 38,000 adults aged 60 and older who received the vaccine. The vaccine also reduced by 66.5% the number of cases of postherpetic neuralgia and reduced the...
and used to reduce the risk of shingles (also called Herpes zoster
Herpes zoster
Herpes zoster , commonly known as shingles and also known as zona, is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body, often in a stripe...
) and Postherpetic neuralgia
Postherpetic neuralgia
Postherpetic neuralgia is a neuralgia caused by the varicella zoster virus. Typically, the neuralgia is confined to a dermatomic area of the skin and follows an outbreak of herpes zoster in that same dermatomic area...
is caused by the same virus, Varicella Zoster Virus
Varicella zoster virus
Varicella zoster virus is one of eight herpes viruses known to infect humans . It commonly causes chicken-pox in children and Herpes zoster in adults and rarely in children.-Nomenclature:...
(VZV), and is simply a larger-than-normal dose of Varivax.
Dangers of chickenpox
Prior to the introduction of vaccine in 1995 in the US (released in 1988 in Japan & Korea), there were around 4,000,000 cases per year in the U.S., mostly children, with typically 10,500–13,000 hospitalizations (range, 8,000–18,000), and 100–150 deaths each year. Though mostly children caught it, the majority of deaths (by as much as 80%) were among adults.During 2003 and the first half of 2004, the CDC reported eight deaths from varicella, six of whom were children or adolescents. These deaths and hospitalizations have substantially declined in the U.S. due to vaccination, though the rate of shingles infection has increased for the same reason. Ten years after the vaccine was recommended in the U.S., the CDC reported as much as a 90% drop in chicken pox cases, a varicella-related hospitalization decline of 71% and a 97% drop in chicken pox deaths among those under 20. In 2006, the shingles vaccine was determined to be effective at preventing shingles (zoster) in persons 60 years of age and older, if administered regularly. In 2011, the FDA approved Zostavax for those 50 to 59 years old.
Vaccination worldwide
Japan was among the first countries to vaccinate for chickenpox. Routine vaccination against varicella zoster virus is also performed in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and the incidence of chickenpox has been dramatically reduced there (from 4 million cases per year in the pre-vaccine era to approximately 400,000 cases per year as of 2005). In Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
most countries do not currently vaccinate against varicella, though the vaccine is gaining wider acceptance. Australia, Canada, and other countries have now adopted recommendations for routine immunization of children and susceptible adults against chickenpox.
Vaccination is common in the United States, with 41 of the 50 states require immunization for children attending government-run schools. All 50 states offer a medical exemption, with 48 of those states also offering philosophical and/or religious exemptions. The vaccination is not routine in the United Kingdom. In the U.S. opinions that it should be dropped (individually or along with all immunizations) are also sometimes voiced.
Other countries, such as Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, have targeted recommendations for the vaccine, e.g., for susceptible health care workers at risk of varicella exposure. In the UK, varicella antibodies are measured as part of the routine of prenatal care, and by 2005 all National Health Service
National Health Service
The National Health Service is the shared name of three of the four publicly funded healthcare systems in the United Kingdom. They provide a comprehensive range of health services, the vast majority of which are free at the point of use to residents of the United Kingdom...
personnel had determined their immunity and been immunized if they were non-immune and have direct patient contact. Population-based immunization against varicella is not otherwise practiced in the UK. It is feared that there would be a greater number of cases of shingles in adults, until the vaccination was given to the entire population—because adults who have had chickenpox as a child are less likely to have shingles in later life if they have been exposed occasionally to the chickenpox virus (for example by their children). This is because the exposure acts as a booster vaccine.
The long-term duration of protection from varicella vaccine is unknown, but there are now persons vaccinated more than thirty years ago with no evidence of waning immunity, while others have become vulnerable in as few as 6 years. Assessments of duration of immunity are complicated in an environment where natural disease is still common, which typically leads to an overestimation of effectiveness, and we are only now entering an era in the U.S. where the long-term efficacy of varicella vaccine can be accurately gauged.
The vaccine is exceedingly safe: approximately 5% of children who receive the vaccine develop a fever or rash, but as of 1 May 2006, there have been no deaths yet attributable to the vaccine despite more than 40 million doses being administered.
Cases of vaccine-related chickenpox have been reported in patients with a weakened immune system, but no deaths.
The literature contains several reports of adverse reactions following varicella vaccination, including vaccine-strain zoster in children and adults.
A mean of 2,350 reports per year are attributed to varicella vaccine based on 20,004 cases reported to the Vaccine Adverse Event Reporting System (VAERS) database from May, 1995 through December, 2003. Minor events are known to be under-reported to VAERS.
Administration
This vaccine is a shot given in the fatty tissue. It is recommended for all children under 13 and for everyone 13 or older who has never had chickenpox.Two doses are always recommended. In the first case a first dose is administered at 12 to 15 months and a second dose at age 4-6 years. For people older than 13 the two doses are administered 4 to 8 weeks apart.
The varicella vaccine is not recommended for seriously ill people, pregnant women, people who have experienced a serious allergic reaction to the varicella vaccine in the past, people who are allergic to gelatin
Gelatin
Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
, people allergic to neomycin
Neomycin
Neomycin is an aminoglycoside antibiotic that is found in many topical medications such as creams, ointments, and eyedrops. The discovery of Neomycin dates back to 1949. It was discovered in the lab of Selman Waksman, who was later awarded the Nobel Prize in Physiology and medicine in 1951...
, people suffering from an immune system disease, such as HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
, people receiving high doses of steroids, people receiving treatment for cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
with x-rays, drugs
DRUGS
Destroy Rebuild Until God Shows are an American post-hardcore band formed in 2010. They released their debut self-titled album on February 22, 2011.- Formation :...
or chemotherapy
Chemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
, as well as people who have received blood products or transfusions during the past 5 months.
Side effects
Serious side effects are very rare. However, in rare occasions, some severe reactions have been reported such as seizuresSeizure
An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
, pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
, and anaphylaxis
Anaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...
.
The possible mild side effects include redness, stiffness
Stiffness
Stiffness is the resistance of an elastic body to deformation by an applied force along a given degree of freedom when a set of loading points and boundary conditions are prescribed on the elastic body.-Calculations:...
, and soreness at the injection site, as well as fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
. A few people may develop a mild rash
Rash
A rash is a change of the skin which affects its color, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell and may be painful. The causes, and...
which usually appears around the shot's area.
There is a risk of developing herpes zoster
Herpes zoster
Herpes zoster , commonly known as shingles and also known as zona, is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body, often in a stripe...
(shingles) following vaccination. However, this risk is less than the risk due to a natural infection resulting in chickenpox. Most of the cases reported have been mild and have not been associated with serious complications.
Effectiveness
According to the American Academy of PediatricsAmerican Academy of Pediatrics
The American Academy of Pediatrics is the major professional association of pediatricians in the United States. The AAP was founded in 1930 by 35 pediatricians to address pediatric healthcare standards. It currently has 60,000 members in primary care and sub-specialist areas...
, clinical trials have demonstrated that varicella vaccine is 70% to 90% effective for preventing varicella and more than 95% effective for preventing severe varicella.
Furthermore, follow-up evaluations took place in the United States of children immunized that revealed protection for at least 11 years. Also, studies were conducted in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
which indicated protection for at least 20 years.
People who do not develop enough protection when they get the vaccine may develop a mild case of the disease when in close contact with a person with chickenpox. In these cases, people show very little sign of illness. This has been the case of children who get the vaccine in their early childhood
Early childhood
For the video game rating with a similar age group see ESRBEarly childhood is a stage in human development. It generally includes toddlerhood and some time afterwards. Play age is an unspecific designation approximately within the scope of early childhood.-Education:Infants and toddlers experience...
and later have contact with children with chickenpox. Some of these children may develop a mild chickenpox also known as breakthrough disease.
Controversy
Mortality due to primary varicella has declined significantly in countries which make wide use of the varicella vaccine.Zoster (shingles) most often occurs in the elderly. Multiple studies have not observed any effect on zoster incidence. This may be because infants and children immunized in varicella vaccination programs have not yet reached the age where zoster typically occurs. It is likewise too early to observe the effect on postherpetic neuralgia
Postherpetic neuralgia
Postherpetic neuralgia is a neuralgia caused by the varicella zoster virus. Typically, the neuralgia is confined to a dermatomic area of the skin and follows an outbreak of herpes zoster in that same dermatomic area...
(PHN).
It has been claimed that adult shingles may increase after introduction of varicella vaccine.
Preliminary evidence that this has occurred is available from data collected from the Antelope Valley Varicella Surveillance Project (VASP) which began surveillance of shingles in 2000. VASP case reports indicate there was a statistically significant increase in adult shingles cases reported to the Antelope Valley Varicella Active Surviellance Project (VASP) from 2000 to 2003. The 56.1% increase from 237 cases in 2000 to 370 cases in 2002 yields a rate ratio of 1.4 (95% C.I. 1.2-1.7). Increases in cases of shingles reported to VASP occurred in every age category (except 70+) from 2000 to 2001. VASP also reported that verified cases of shingles among adults aged 50 years and older increased 27.5% from 2006 to 2007. (Annual Summary, 2001, 2002, 2003, 2006, 2007 Antelope Valley Varicella Active Surveillance Project, Los Angeles County Department of Health Services; Centers for Disease Control and Prevention (CDC) Cooperative Agreement No. U66/CCU911165-10; Mascola L, et al.)
Additional controversy has arisen because cell lines derived from aborted fetal tissue were used in its development, and thus violates the ethics and beliefs of people who oppose the use of aborted fetal tissue in medical research.
Duration of immunity
Some vaccinated children have been found to lose their protective antibody in as little as five to eight years. However, according to the World Health OrganizationWorld Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
: "After observation of study populations for periods of up to 20 years in Japan and 10 years in the United States, more than 90% of immunocompetent persons who were vaccinated as children were still protected from varicella." However, since only one out of five Japanese children were vaccinated, the annual exposure of these vaccinees to children with natural chickenpox boosted the vaccinees' immune system. In the United States, where universal varicella vaccination has been practiced, the majority of children no longer receive exogenous (outside) boosting, thus, their cell-mediated immunity to VZV (varicella zoster virus) wanes--necessitating booster chickenpox vaccinations.
Some persons exposed to the virus after vaccine can experience milder cases of chicken pox (and usually then harbor both the attenuated vaccine or oka strain as well as the wild type or natural chickenpox strain which are both subject to reactivation as shingles).
Catching "wild" chickenpox as a child has been thought to commonly result in lifelong immunity. Indeed, parents have deliberately ensured this in the past with "pox parties" (see below). Historically, exposure of adults to contagious children has boosted their immunity, reducing the risk of shingles.
The CDC and corresponding national organisations are carefully observing the failure rate which may be high compared with other modern vaccines - large outbreaks of chickenpox having occurred at schools which required their children to be vaccinated.
Immunocompromise
The mortality rate in immunocompromised patients with disseminated herpes zoster is 5-15%, with most deaths from pneumoniaPneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
. Vaccines are less effective among these high-risk patients, as well as being more dangerous because they contain attenuated live virus (see last footnote). In a study performed on children with an impaired immune system
Immunodeficiency
Immunodeficiency is a state in which the immune system's ability to fight infectious disease is compromised or entirely absent. Immunodeficiency may also decrease cancer immunosurveillance. Most cases of immunodeficiency are acquired but some people are born with defects in their immune system,...
, 30% had lost the antibody after five years, and 8% had already caught wild chickenpox in that five year period.
Pox parties
A "pox party" is a party held by parents for the purpose of infecting their children with childhood diseases. Similar ideas have applied to other diseases, e.g. measlesMeasles
Measles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...
, but are now discouraged by doctors and health services due to the risk of serious injury or death (even in children, as described above) from acquiring the disease. The reasoning behind such parties is that guests exposed to the varicella virus will contract the disease and develop strong and persistent immunity
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
at an age before disaster is likely, particularly from chickenpox or rubella
Rubella
Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...
. The first reference to such a practice is the letter of Lady Montagu to Sarah Chiswell describing parties held in Istanbul for the purpose of variolation—an effective technique for gaining immunity to smallpox
Smallpox
Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...
. Lady Montagu imported variolation to England.