Health Advisory
2009-2010 Influenza Season Update #15

Live Attenuated Influenza Vaccine (LAIV or Nasal Spray Vaccine)

To: Vermont Health Care Providers
From: Wendy Davis, MD, Commissioner
Date: December 11, 2009

– Please Distribute Widely –

To date, about 20 percent of the 2009 H1N1 vaccine supply in Vermont has been in the Live Attenuated Influenza Vaccine (LAIV) form. This means that, as much as possible, people who are eligible should only be offered the nasal spray vaccine, and not the flu shot, to conserve supplies of flu shot for those who cannot have the nasal spray form of vaccine.

The nasal spray is recommended for healthy people age 2 through 49 who are not pregnant.

This includes the following groups:

We are aware that some patients and health care workers are concerned about taking a vaccine that contains a live attenuated virus, or think that this form of the vaccine may not be as effective as the flu shot.

Live attenuated virus

Like a number of other vaccines, the nasal spray form of the 2009 H1N1 vaccine contains a weakened form of the virus that cannot survive at body temperature. It cannot give a person the flu, and it will not put anyone around a vaccinated person at risk for the flu. The only exception to this is severely immunocompromised patients. The 2009 H1N1 nasal spray vaccine does not contain thimerosal or other preservatives.

More specifically, the virus strain in LAIV is cold-adapted – it replicates efficiently at 25ºC, a temperature that restricts replication of many wild-type influenza viruses.  It is also temperature-sensitive – it is restricted in replication at 39C, a temperature at which many wild-type viruses grow efficiently.  And it is attenuated and therefore does not produce classic influenza-like illness in the ferret model of human influenza infection. See full prescribing information at:

Efficacy of Vaccine

LAIV, the nasal spray flu vaccine, was first approved for use against seasonal influenza in 2003. Studies conducted in comparison with injectable seasonal influenza vaccine (the flu shot) have demonstrated safety and efficacy, especially among children younger than 6 years of age, and also against seasonal strain drift variants that were antigenically dissimilar from vaccine strains. A recent report comparing seasonal nasal spray vaccine to seasonal flu shot vaccine found lower efficacy (29%) in healthy 18- to 49-year-old subjects who received seasonal nasal spray vaccine in contrast to flu shot vaccine (72%), or a relative efficacy of 50%.


The study’s authors theorize that age-related immunity to seasonal flu strains due to prior exposure to related seasonal strains may play a role in the difference noted. It remains unclear how the findings in the study noted above inform decisions about what vaccine formulation to use in 2009 H1N1 vaccination efforts. More clearly, there are compelling reasons to encourage those who are eligible to receive the nasal spray to receive this formulation to conserve limited supplies of flu shot for people who have contraindications for the nasal spray.

LAIV and Health Care Personnel

From CDC’s FAQS on this topic - 10.08.09:

LAIV is a good option for most health care providers who are healthy, younger than 50 years, and not pregnant. However, health care providers should not get the nasal spray vaccine if they are providing medical care for patients who require special protected environments in the hospital because they are severely immunocompromised (e.g., those who work in bone marrow transplant units). Although no immunocompromised patient has been shown to be harmed by use of nasal spray vaccine among health care workers, the recommendation against the use of this form of vaccine in health care workers with this type of patient contact is intended as an extra precaution for fragile immunocompromised patients. Health care workers with this type of patient contact can get the nasal spray vaccine, but if they do, they should wait seven days after being vaccinated before returning to duties that include care of severely immunocompromised patients in special environments.

Below is a link to a report about the status of LAIV in the U.S. See the safety profile section for specific information on shedding and spread of LAIV to contacts:  

You may also be interested in the current Healthcare Infection Control Practices Advisory Committee (HICPAC) isolation guidelines: 

These guidelines detail “Protective Environment” precautions indicated for stem cell transplant recipients during times of greater risk for acquiring infections.

For more information, see the Centers for Disease Control (CDC) Q&A on Nasal Spray Vaccines:

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