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Live-attenuated vaccines Live vaccines use a weakened form of the germ that causes a disease

February 20, 2019 0 Comment

Live-attenuated vaccines
Live vaccines use a weakened form of the germ that causes a disease.
Because these vaccines are parallel to the natural infection that they help to prevent, they generate a strong and long-lasting immune response. due 1 or 2 doses of most live vaccines can give you a lifetime of defense against a germ and the disease it causes.
But live vaccines also have some termination.
Because they contain a small amount of the weakened live virus, some people should talk to their health care provider before receiving them, such as people with weakened immune systems, long-term health problems, or people who’ve had an organ transplant.
They need to keep cool, so they don’t travel well. That means they can’t be used in countries with limited access to refrigerators.
Live vaccines are used to protect against:
• Measles, mumps, rubella (MMR combined vaccine)
• Rotavirus
• Smallpox
• Chickenpox
• Yellow feve
Measles, mumps, rubella (MMR combined vaccine)
Measles is caused by Measles virus, an RNA virus of the Paramyxoviridae family.
It most commonly affects young children.
While Rare in the US, it is endemic in various parts of Asia and Africa.
Available as
MMR: Combination of Measles, Mumps, and Rubella vaccines.
MMRV: Combination of Measles, Mumps, Rubella, and Varicella vaccines

Effectiveness
MMR Single dose 93% effective.
Two doses about 97% effective.
Usage
Children: All children should be vaccinated against measles. Two doses are usually required: First one at 12-15 months of age, and a booster dose at 4-6 years of age.
Adults: Adults who are unvaccinated and who had never had measles should receive at least one dose of the vaccine (preferably two). High-risk people like college students, international travelers, and health-care workers should get two doses. The doses should be separated by a period of at least 28 days.
Pregnant women: All unvaccinated women planning to become pregnant should be vaccinated at least 1 month before getting pregnant. The vaccine should not be used during pregnancy. (Unprotected, pregnant women should wait till they have given birth before getting MMR/MMRV vaccine.)
Rubella or German Measles is caused by Rubella virus, an RNA virus of the Togaviridae family.
It most commonly affects young children. If contracted during pregnancy, Rubella can cause serious birth defects in the newborn.
Mumps is an acute viral infection of parotid glands. It is caused by mumps virus, an RNA virus of the Paramxyoviridae family.
It most commonly affects young children. Orchitis is a potentially serious complication which may lead to infertility.
Rota virus is an important cause of severe gastroenteritis in infants and young children, around the world.
Rota virus is an RNA virus of the Reoviridae family, transmitted by oral-fecal route.
While many cases are mild and easily manageable, severe rotavirus gastroenteritis can lead to life-threatening dehydration.
Available as
RV5: A pentavalent live-attenuated vaccine containing five human-bovine reassortant rotaviruses, given orally.
RV1: A monovalent live-attenuated vaccine that contains a human rotavirus strain (type G1p1A), given orally

Effectiveness
None of the vaccines is currently considered preferable over the other.
Efficacy studies demonstrated that rotavirus vaccine was 85%-98% protective against severe rotavirus disease and 74%-87% protective against rotavirus disease of any severity through approximately the first rotavirus season.
Usage
Routine Vaccination:
All children should be vaccinated against Rotavirus using either RV5 or RV1.
RV5: 3-dose schedule is used, given at 2, 4 and 6 months of age.
RV1: 2-dose schedule is used, given at 2 and 4 months of age.
Vaccination should be completed before the end of 8th month of life.
Minimum interval between two doses is at least 4 weeks.
Children who’ve had a rotavirus infection before should still receive the complete course of vaccination because one infection might provide only partial immunity against further rotavirus infections.
Precautions
Contraindications:
Children who’ve had severe allergic reaction to previous dose of the vaccine or who are allergic to any component of the vaccine (including latex in case of RV1).
Children diagnosed with severe combined immunodeficiency (SCID).
Infants with a history of intussusception.
Precautions:
Rotavirus vaccine may not be suitable for some immunocompromised children. Consultation with immunologist or infectious disease specialist is advised.
Child with mild acute illness including mild gastroenteritis can be vaccinated. However those with moderate to severe gastroenteritis or febrile illness are advised to wait until their condition improves.

Smallpox is caused by Smallpox virus (Variola virus), a DNA virus of the Poxviridae family.
Smallpox used to be a significant cause of mortality and morbidity around the globe before it was eradicated through world-wide vaccination.
At the current state of events it is considered to be a disease of the past, the last case of naturally occurring smallpox being diagnosed in 1977 in Somalia.
Available as
Smallpox Vaccine: It contains the live Vaccinia virus (a virus closely related to smallpox and cowpox virus).

Usage
Smallpox has been declared to be eradicated globally and routine vaccination is offered no more.
The vaccine is now used for protection of scientists and healthcare workers who are involved in research related to smallpox virus.
Since 2001, US and UK started stockpiling smallpox vaccine to prepare against any possible bio-terror attack. Center for Disease Control (US) states that they have stockpiled enough smallpox vaccines to vaccinate every person in the US in case of a smallpox emergency.
Some US armed forces personnel deployed in Middle East and other areas outside US are also vaccinated against smallpox.
Precautions
Should not be used in:
Patients who had severe allergic reaction to a previous dose of MMR or MMRV vaccine, Neomycin, Gelatin, or any other component of the vaccine.
Pregnant women.
Patients with AIDS, Cancer or undergoing radiotherapy.
Consult before usage if:
Persons who are immunodeficient due to any reason,
Pregnant women,
People allergic to a previous dose of the vaccine or any component of the vaccine.
(Visit CDC’s website for details regarding contraindications, precautions and other information about smallpox vaccine)
Chickenpox (Varicella) is caused by Varicella-Zoster Virus (VZV), a DNA virus of the Herpesviridae family.
Available as
Varicella (Varivax): single antigen Varicella vaccine.
MMRV: combination of Measles, Mumps, Rubella, and Varicella vaccines.
(The following discussion is about single antigen Varicella vaccine, for MMRV see Measles Vaccines).
Effectiveness
MMR Single dose 85% effective.
Two doses about 88-98% effective.
Vaccinated people can get Chickenpox but the disease is usually milder and short-lived.
Usage
Children: Children aged 12 months – 12 years should be vaccinated against chickenpox with either Varicella vaccine or MMRV. Varicella vaccine: 2 doses given subcutaneously at least 3 months apart.

Adults: Persons above 13 years age who are unvaccinated and who had never had chickenpox should receive two doses of varicella vaccine, given at least 28 days apart.
Pregnant women: Vaccine should not be used in pregnant women. Women should wait at least 28 days after vaccination before getting pregnant.
Precautions
Should not be used in:
Patients who had severe allergic reaction to previous dose of the vaccine, Neomycin, Gelatin, or any other component of the vaccine.
Pregnant women.
Patients having leukemia/lymphoma, blood dyscrasias, and thrombocytopenia.
Patients with family history of congenital immunodeficiency disease (unless they are immunocompetent) or receiving high-dose immunosuppressant therapy (including steroids).
Patient who had blood/blood products transfusion during the past 11 months.
Acutely ill patients may not be vaccinated until they have recovered.
Salicylates (Aspirin) should be avoided for 6 weeks after getting the vaccine because of the potential risk of Reye Syndrome.
Yellow fever is a serious hemorrhagic viral disease, caused by Yellow Fever Virus, an RNA virus of Flaviviridae family.
It manifests with fever, jaundice and hemorrhagic phenomenon.
The disease is endemic in South America and tropical Africa.
Available as
YF Vaccine 17D: Contains the 17D strain of yellow fever virus, which is live-attenuated. It is given subcutaneously or intramuscularly as a single shot.

Effectiveness
Human studies regarding the efficacy of YF vaccine are limited. However, retrospective observations suggest that the vaccine is highly effective in prevention of YF.
World-wide only 5 cases of YF have been reported in those who have been vaccinated since the vaccine has been in use.
Usage
The vaccine is recommended for anyone older than 9 months who is living in or travelling to an area where Yellow fever is common. It is given as a single dose vaccine, which provides long-term immunity. A booster dose after 10 years may be considered for those who continue to be at risk of acquiring YF.
Some countries require certificate of yellow fever vaccination before allowing entry to a person.
YF vaccine is recommended for laboratory personnel who might be exposed to virulent YFV or to concentrated preparations of YF vaccine virus strains by direct or indirect contact or by aerosols.
Precautions
Contraindicated in:
Infants less than 6 months old.
Safety has not been established for those aged 6-8 months. Such infants should only be vaccinated if an outbreak of YF occurs.
Persons severely allergic to egg protein or any other component of the vaccine.
Immunocompromised individuals like those having HIV/AIDS, primary immunodeficiency, or those taking using immunosuppressive drugs.
Use in pregnancy:
Insufficient evidence is present regarding the safety of YF vaccine during pregnancy and breastfeeding. It is concluded that the potential benefits of vaccination are likely to far outweigh the potential risks in women living in YF endemic areas or in case of outbreaks.
In other situations, the women should be informed regarding the potential adverse effects of the vaccine and if possible travel to YF endemic areas be postponed.

Advantages and disadvantages of live attenuated vaccine
Advantages
• Activates all phases of the immune system (for instance IgA local antibodies are produced)
• Provides more durable immunity; boosters are required less frequently
• Low cost
• Quick immunity
• Some are easy to transport/administer (for instance OPV for polio can be taken orally, rather than requiring a sterile injection by a trained healthworker, as the inactivated form IPV does)
• Vaccines have strong beneficial non-specific effects. That is effects which go beyond the specific protective effects against the targeted diseases.
Disadvantages
• Secondary mutation can cause a reversion to virulence
• Can cause severe complications in immunocompromised patients.
• Some can be difficult to transport due to requirement to maintain conditions (e.g. temperature)