Live attenuated influenza vaccine
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Live attenuated influenza vaccine (LAIV) is a type of influenza vaccine in the form of a nasal spray. It is an attenuated vaccine, unlike most influenza vaccines, which are inactivated vaccines. LAIV is administered intranasally, while inactivated vaccines are administered by intramuscular injection. Both live attenuated and inactivated vaccines are typically trivalent. That is, they contain material from three different influenza virus strains recommended by national and international public health agencies as most likely to be protective against seasonal influenza in any given year. LAIV is sold under the trade name FluMist in the United States and Fluenz in Europe.
FluMist is manufactured by MedImmune and was first introduced in 2003. It was the first and (as of 2007) the only live attenuated vaccine for influenza available outside of Europe. In September 2009 a LAIV intranasal vaccine for the novel H1N1 influenza virus was approved. In 2011, the vaccine was approved by the European Medicines Agency for use in the European Union under the name Fluenz.
Even though the virus in LAIV is attenuated (low in virulence), it is still a living virus, and may cause an infection with complications in people with weakened immune systems or other underlying medical conditions. LAIV is recommended only for people 2–49 years of age, and is not recommended for people who have a weakened immune system, for pregnant women, or for people with certain chronic diseases. In contrast, inactivated virus vaccines contain no living virus, and cannot cause a live infection. Persons receiving LAIV may shed small amounts of the vaccine virus during the first week. People coming in contact with the vaccinated person are not considered to be at risk, unless their immune systems are severely weakened (bone marrow transplant recipients).
Source of LAIV 
MedImmune is one company that manufactures LAIV, which it sells under the trade name "FluMist" in the United States and "Fluenz" in Europe. For the 2010–2011 flu season, FluMist was the only LAIV approved by the FDA for use in the USA. All other FDA-approved lots were inactivated virus vaccines. In September 2009 a LAIV intransal vaccine for the novel H1N1 influenza virus was approved and the seasonal intranasal vaccine was approved by the European Medicines Agency for use in the European Union in 2011, though distribution will not likely begin until 2012.
Groups for whom FluMist is recommended 
In Canada, the National Advisory Committee on Immunization (NACI), the group that advises the Public Health Agency of Canada, currently recommends that everyone aged 2 to 64 years be encouraged to receive annual influenza vaccination, and that children between the age of 6 and 24 months, and their household contacts, should be considered a high priority for the flu vaccine.
In February 2008, the U.S. Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) recommended vaccination for all children and teenagers between six months and 18 years of age.
FluMist is a vaccine of demonstrated effectiveness against seasonal influenza. Reviews conducted in 2008 and 2011 suggest that FluMist may be equal to or more effective than injected influenza vaccines in children aged 6–71 months and in children aged 6–17 years.
In 2007, FluMist received additional approval from the U.S. Food and Drug Administration (FDA) extending the age groups it is approved for, to include healthy children two years old and onward. And the CDC's Advisory Committee on Immunization Practices (ACIP), endorsed the needle-free vaccine as a good option for healthy (non-asthmatic) children aged 2 through 4 years. This extended approval supplemented approvals for children over four years of age that were already effective. The sum of these approvals is that FluMist is approved and recommended from the child's 25th month through the adult's 49th year of age.
FluMist is currently recommended for all healthy persons at least two years old and under 50 years of age wishing to protect themselves from influenza and its complications, or to avoid spreading the flu to members of certain vulnerable groups:
"All healthy, non-pregnant persons age 49 yrs and younger who want to reduce the likelihood of becoming ill with influenza, or of spreading it to others who meet any of the criteria listed below:
-Working or living with at-risk people as listed in the section above.
-Healthcare personnel or other persons who provide direct care to at-risk people (except persons in close contact with severely immunosuppressed persons).
-Household contacts and out-of-home caregivers of children age 0–59m.
-Travelers who may be among people from areas of the world where there is current influenza activity (e.g., on organized tours).
-Students or other persons in institutional settings (e.g., dormitory residents)." 
For comparison, only Sanofi-Aventis's injectable influenza vaccine is approved for children 7 months of age and older; FluMist is approved after the second year, and other injectable vaccines from four years of age onward. Injectable influenza vaccine approvals have no upper age limit, while FluMist has not yet been tested or presented for FDA approval for use by persons 50 or older.
Within the age groups they are approved for, injectable vaccines do occasionally present mild side effects such as soreness, redness, swelling, fever, and aches, and FluMist sometimes causes brief and mild symptoms such as a runny nose. Side effects of both FluMist and injected vaccines tend to be slightly more prevalent the first year, and to diminish with vaccinations given in subsequent years.
Tests against injected (killed virus) vaccinations have shown that FluMist is more effective than needle shots in preventing influenza, especially in children aged 6 to 17 but one smaller study in adults showed lower effectiveness against influenza B viruses in adults.
In past years when flu vaccine has been in short supply, healthy people were requested to abstain from vaccination early in the season, to leave the limited supply for the most vulnerable groups. Flu vaccine supplies are now abundant, and since healthy people benefit from vaccination they are now encouraged to protect themselves and others by being vaccinated.
The 2007 recommendations by the US Advisory Committee on Immunization Practices (ACIP) include six principal changes or updates. These stress that all persons who want to reduce the risk of becoming ill with influenza or of transmitting influenza to others should be vaccinated, and that young children not previously vaccinated should be vaccinated twice, and include these specific recommendations:
ACIP reiterates a previous recommendation that all persons, including school-aged children, who want to reduce the risk of becoming ill with influenza or of transmitting influenza to others should be vaccinated (see Box and Recommendations for Using TIV and LAIV During the 2007--08 Influenza Season).
ACIP emphasizes that immunization providers should offer influenza vaccine and schedule immunization clinics throughout the influenza season (see Timing of Vaccination).
ACIP recommends that health-care administrators consider the level of vaccination coverage among health-care personnel (HCP) to be one measure of a patient safety quality program and implement policies to encourage HCP vaccination (e.g., obtaining signed statements from HCP who decline influenza vaccination) (see Additional Information Regarding Vaccination of Specific Populations).
In 2000, a study found FluMist be well tolerated in 57 adults with asymptomatic HIV and median CD4 counts of 541. The FluMist patient information further clarifies, "Although FluMist was studied in 57 asymptomatic or mildly symptomatic adults with HIV infection [...], data supporting the safety and effectiveness of FluMist administration in immunocompromised individuals are limited." In 2008, FluMist was tested and found safe for children suffering from HIV and taking anti-retrovirals.[dead link]
However, the U.S. Centers for Disease Control state clearly that people with HIV/AIDS should not receive FluMist  and that advice is augmented by the suggestion that close household contacts or caregivers of severely immunocompromised individuals should not receive FluMist due to transmission risks from individuals immunized with FluMist.
The vaccine was approved for use in the European Union by the European Medicines Agency in 2011. Marketing approval in Europe, where it will be called Fluenz, is for the prevention of seasonal influenza in children aged from two to less than 18 years, though distribution will not likely begin until 2012.
Groups for whom FluMist is not recommended 
- People less than 2 years of age
- People 50 years of age and over
- People with a medical condition that places them at high risk for complications from influenza, including those with chronic heart or lung disease, such as asthma or reactive airways disease
- People with medical conditions such as diabetes or kidney failure or people with illnesses that weaken the immune system, or who take medications that can weaken the immune system
- Children less than 5 years old with a history of recurrent wheezing
- Children or adolescents receiving aspirin
- People with a history of Guillain-Barré syndrome, a rare disorder of the nervous system
- Pregnant women
- People who have a severe allergy to chicken eggs or who are allergic to any of the nasal spray vaccine components
It is possible for individuals vaccinated with FluMist to spread the virus to others for up to 21 days after vaccination. For this reason it is recommended that those vaccinated with FluMist avoid close contact with individuals with weak immune systems during that time.
Testing pandemic FluMist variants 
FluMist is designed to be quickly modifiable to present the surface antigens of seasonal flu. The modifiability could also allow it to be quickly customized as a vaccine against a pandemic influenza if one were to emerge. In light of the Global spread of H5N1 advance preparation to reduce human mortality in the event of an H5N1 pandemic has begun. Modifying FluMist to serve as a specific human H5N1 vaccine is among the measures studied.
In June 2006, the National Institutes of Health (NIH) began enrolling participants in a Phase 1 H5N1 study of an intranasal influenza vaccine candidate based on MedImmune's live, attenuated vaccine technology.
In September 2006 the NIH NIAID reported that inoculation with a FluMist vaccine modified to present the surface antigens of certain H5N1 variants provided broad protection against other H5N1 variants in the mouse and ferret models. Attenuated live viruses were found protective against H5N1 in mice and chickens in a 2009 study.
Although early work is focusing on the looming H5N1 threat, the CDC team led by Kanta Subbarao and others intends to eventually prepare and store surface antigens for all known strains of influenza, ready to be grafted onto the base attenuated FluMist core virus whenever a pandemic threat might emerge.
"Several trials have reported that LAIVs can boost virus-specific CTLs as well as mucosal and serum antibodies and provide broad cross-protection against heterologous human influenza A viruses." (58, 59) "[V]accine formulas inducing heterosubtypic T cell–mediated immunity may confer broad protection against avian and human influenza A viruses." 
In September 2009 a LAIV intranasal vaccine for the novel H1N1 influenza virus was approved.
FluMist was originally developed by Hunein "John" Maassab, Professor of Epidemiology at the University of Michigan School of Public Health in Ann Arbor, Michigan and later by Aviron, in Mountain View, California, under the sponsorship of NIH in the mid-1990s. MedImmune, Inc. purchased Aviron in 2002, and the FDA approved FluMist in June 2003. FluMist was first made available in September 2003.
The U.S. FDA initially approved FluMist only for healthy people ages 5 to 49 because of concerns over possible side effects. Now FluMist is approved and recommended for healthy children 24 months of age and older. The FDA approved the current unfrozen refrigerated version for the same age group (ages 5–49) in August 2006 following completion of phase 3 clinical trials. CAIV-T has been approved by the FDA and is the version offered on the market beginning in fall of 2007.
The current version of the vaccine is called CAIV-T, and is stable for storage in a refrigerator, rather than requiring freezer storage as did the originally-approved formulation. Approved for the 2007-2008 flu season, the refrigerated formulation can be distributed more economically, so that the price differential with shots (which had hampered sales of the original frozen version of FluMist) is now largely eliminated. FluMist was initially priced higher than the injectable vaccines, but sold only 500,000 of the 4 million doses it produced its first year on the market, despite a comparative shortage of flu vaccine in fall 2004. The price was sharply lowered the next year, and the company reports distributing 1.6 million doses in 2005. Because of the price drop, despite selling almost three times as many doses in 2005, the company reported $21 million in FluMist sales, compared to $48 million the previous year. Further cuts in pricing had to await FDA approval of a refrigerator-cooled FluMist formulation, as the initial formulation required freezer storage and thawing on demand before administration. Although it is positioned as a premium product, the remaining price premium for FluMist over the cost of needle-injected vaccine is small.
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