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Facts about the H1N1 Vaccine

by Dr. Chris Nelson

Supplies of the H1N1 influenza vaccine have finally started trickling into Kentucky.  As of Nov. 11, nearly half a million doses had been shipped to the Commonwealth.  Local health departments are allocating these on a priority need basis.

Last week, 2,000 doses of the vaccine  were made available to the University of Kentucky campus community, free of charge, on a first-come, first-serve basis. Early response was encouraging, with hundreds of people lining up outside the clinic before it even opened.

The safety and efficacy of H1N1 vaccines in clinical studies has been comparable to that of seasonal flu vaccines. Still, there are a lot of misconceptions circulating about the H1N1 vaccine that might deter people who really should be vaccinated. 

The Centers for Disease Control and Prevention (CDC) have identified priority groups who should be vaccinated first.  These include pregnant women, persons who care for infants, all persons ages 6 months through 24 years, health-care and emergency medical services personnel, and persons ages 24-64 who have medical conditions that put them at higher risk for influenza-related complications.

However, nearly everyone should be vaccinated when supplies of the vaccine become more plentiful. A total of 250 million doses are being prepared, enough to protect nearly every person in the country.  Because of something called "herd immunity," the level of protection against illness increases for everyone – even those few who cannot be vaccinated – as more people receive the vaccine.

Vaccine is being shipped as live attenuated influenza vaccine (LAIV) for intranasal use and as an intramuscular, injectable killed-virus vaccine.  LAIV is licensed for and should only be taken by healthy non-pregnant persons 2-49 years of age who do not have any chronic medical conditions. The injectable vaccine is in very limited supply and is reserved for patients who cannot receive LAIV. 

LAIV contains a live version of the novel H1N1 virus that has been genetically altered in two important ways so that it cannot cause invasive infection or symptoms. First, the virus is cold-adapted, so it can only replicate at temperatures lower than 77 degrees Fahrenheit. In the human body, this means that it can only replicate in the nasopharynx (the area behind the nasal cavity just above the throat), and not in the lungs.  Secondly, the virus is attenuated, or weakened, so that it cannot cause symptoms or disseminate to spread disease.

Many people are aware that there was a slight increase in the number of people who developed Guillain-Barre syndrome during the 1978 Swine Flu Pandemic. It is unknown whether this was related to natural exposure to this strain of influenza virus – Guillain-Barre syndrome is a rare, but recognized complication of influenza infection –  or whether this was because of the vaccine given to interrupt this pandemic. Available safety data on this year’s seasonal and H1N1 vaccines has not revealed any adverse reactions beyond common local injection site reactions.

For up-to-date information about the novel H1N1 influenza vaccine, see the following Web sites:

·         CDC 2009 Novel H1N1 Vaccine site:

·         Flu Information from U.S. Department of Health & Human Services:

·         Kentucky Health Alerts:


Dr. Chris Nelson is UK Healthcare Enterprise Medical Director for Infection Prevention and Control.