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Weakened live viral vaccines are designed in the laboratory to cause few symptoms in recipients while giving them immunity against future infections. Polio was one disease that represented a milestone in the use of vaccines. Mass immunization campaigns in the U.S. in the 1950s (killed vaccine) and 1960s (live vaccine) essentially eradicated the disease, which caused muscle paralysis in children and generated fear in the general population when regional epidemics occurred. The success of the polio vaccine paved the way for the routine dispensation of childhood vaccines against measles, mumps, rubella, chickenpox, and other diseases.

Live vaccines are usually made by attenuation    (weakening) of the “wild-type” (disease-causing) virus by growing it in the laboratory in tissues or at temperatures different from what the virus is accustomed to in the host. For example, the virus may be grown in cells in a test tube, in bird embryos, or in live animals. The adaptation to these new cells or temperature induces mutations in the virus’ genomes, allowing them to grow better in the laboratory while inhibiting their ability to cause disease when reintroduced into the conditions found in the host. These attenuated viruses thus still cause an infection, but they do not grow very well, allowing the immune response to develop in time to prevent major disease. The danger of using live vaccines, which are usually more effective than killed vaccines, is the low but significant risk that these viruses will revert back to their disease-causing form by back mutations. Back mutations occur when the vaccine undergoes mutations in the host such that it readapts to the host and can again cause disease, which can then be spread to other humans in an epidemic. This happened as recently as 2007 in Nigeria where mutations in a polio vaccine led to an epidemic of polio in that country.

Some vaccines are in continuous development because certain viruses, such as influenza and HIV, have a high mutation rate compared to other viruses or host cells. With influenza, mutation in genes for the surface molecules helps the virus evade the protective immunity that may have been obtained in a previous influenza season, making it necessary for individuals to get vaccinated every year. Other viruses, such as those that cause the childhood diseases measles, mumps, and rubella, mutate so little that the same vaccine is used year after year.

Vaccines and antiviral drugs for treatment

In some cases, vaccines can be used to treat an active viral infection. In the case of rabies, a fatal neurological disease transmitted in the saliva of rabies virus-infected animals, the progression of the disease from the time of the animal bite to the time it enters the central nervous system may be two weeks or longer. This is enough time to vaccinate an individual who suspects being bitten by a rabid animal, and the boosted immune response from the vaccination is enough to prevent the virus from entering nervous tissue. Thus, the fatal neurological consequences of the disease are averted and the individual only has to recover from the infected bite. This approach is also being used for the treatment of Ebola, one of the fastest and most deadly viruses affecting humans, though usually infecting limited populations. Ebola is also a leading cause of death in gorillas. Transmitted by bats and great apes, this virus can cause death in 70–90 percent of the infected within two weeks. Using newly developed vaccines that boost the immune response, there is hope that immune systems of affected individuals will be better able to control the virus, potentially reducing mortality rates.

Questions & Answers

which structure consists of a phospholipid bilayers and it is known as the mosaic model?
Jamar Reply
what is diffusion
Patricia Reply
a passive process of transport
Jamar
10 difference between male and female reproductive system
Ina Reply
if a phase is omitted ,what will happen to the cell
Ewemoje Reply
discribe advantages and disadvantages of asexual and sexual reproduction
basi Reply
Compared to separate sexes and assuming self-fertilizing is not possible, what might be one advantage and one disadvantage to hermaphroditism?
Gift Reply
is nature of their environment among
basi
cool 😎
Precious
why are the laws of thermodynamics considered laws of nature and not scientific theories
Yolonda Reply
archea were given their own separate domain because they are?
Yolonda
which of the following is a basic component of all of the others?
Yolonda
which of the following organization levels is the least inclusive
Yolonda
which cell feature is absent in bacterial cells
Yolonda
which metric movies the base unit of measurement by one thousandth (0.001)?
Yolonda
What is biology?
Blessing Reply
List the branches of biology
Blessing
List the branches of biology
Blessing
List the branches of biology
Blessing
List the branches of biology
Blessing
must all prokaryotic cells posses a cell wall?
chris Reply
what is biology?
Cathy Reply
biology is basically the study of life
Robert
that's true
Tonia
it's the study of living things
Tonia
biology is defined as the study of living and nonliving things
Ina
Biology is not only the study of life but it is the study of death too.
Koushik
What is a celiac disease
Falase Reply
distinguish between properties and characteristics
Elee Reply
what are organelles
Elee
organelles are substances that makes up a cell
chris
organelles are special features of a cell that perform a specific task
Enock
what is biology
Prevail Reply
biology is science that studies life
Elee
it's the study of living and non living things
now that we have an estimate for the diameter of the cell.what estimate can we make about the volume of the cell?
faxhood Reply
why too much insulin result in low blood sugar
Leri Reply
For example, too much exercise can cost you to lose to much weight. Too much insulin will pull to much sugar out of your systemic system into your cells.
Eric

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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