The 2009 H1N1 Influenza A is a type of influenza (flu) virus that causes respiratory disease that can spread between people. Most people infected with this virus in the United States have had mild disease, but some have had more severe illness and even died. Individuals aged 6 months to 24 years of age, pregnant women, and people aged 25 to 64 years of age with chronic diseases like asthma, diabetes, or heart disease are at higher risk for complications from this infection.  There are steps you can take to prevent the spread of the flu: Clean your hands, Cover your cough or sneeze with a tissue or sleeve, and Contain the flu by staying home if you are sick with flu-like symptoms.  Also, get the 2009 H1N1 Influenza A vaccine, once it is available.

The symptoms of the 2009 H1N1 Influenza A (flu) are similar to the symptoms of seasonal flu. They include: 

• Fever of more than 100 degrees F
• Cough 
• Sore throat 
• Body aches 
• Headache 
• Chills and fatigue 
• Occasionally, vomiting and diarrhea

H1N1 influenza vaccination

The Immunization Action Coalition has published the following “Ask the Experts” edition regarding H1N1 vaccination. Focused solely on vaccination against H1N1 influenza, the Q&As in this "Ask the Experts" edition will give healthcare providers some of the information they need to start immunizing immediately once H1N1 influenza vaccine becomes available. IAC thanks William L. Atkinson, MD, MPH, and Andrew T. Kroger, MD, MPH, medical epidemiologists, at the National Center for Immunization and Respiratory Diseases, CDC, for agreeing to answer the following questions.

Q: When will vaccine for the 2009 H1N1 influenza virus be available?

A: CDC estimates that approximately 45 million doses of H1N1 influenza vaccine will be available in mid-October. CDC anticipates that approximately 20 million additional doses will be released in each subsequent week. Keep in mind that vaccine availability is driven by a number of variables in the manufacturing process. Once vaccine is available, vaccination should begin immediately.

Q: Is the 2009 H1N1 influenza vaccine experimental?

A: No. H1N1 influenza vaccine will be available in an inactivated, injectable formulation and a nasal-spray, live attenuated formulation. Neither is an experimental vaccine. The 2009 H1N1 influenza vaccines are made employing the same methods and facilities used annually to produce seasonal influenza vaccine. The vaccines are undergoing additional clinical trials at this time to determine the size of the dose and the number of doses that will be needed for protection.

Q: Once a 2009 H1N1 influenza vaccine becomes available, who will be targeted to receive the vaccine?

A: On August 28, 2009, CDC issued recommendations for the use of the 2009 H1N1 influenza vaccine. The recommendations identify 5 initial target groups for H1N1 influenza vaccination. They are (1) pregnant women; (2) people who live with or provide care for infants younger than age 6 months (e.g., parents, siblings, day care providers); (3) healthcare and emergency medical services personnel; (4) children and young adults ages 6 months through 24 years; and (5) people ages 25 through 64 years who have medical conditions that put them at higher risk for influenza-related complications. You can access the complete recommendations at http://www.cdc.gov/mmwr/PDF/rr/rr5810.pdf

Q: Why are pregnant women prioritized for vaccination?

A: Data from early 2009 H1N1 influenza cases in the United States show that pregnant women account for a disproportionate number of deaths, making them a high-priority group for vaccination (see http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(09)61304-0/abstract). Also, guidance has been issued for clinicians to promptly treat pregnant women who become infected with the 2009 H1N1 virus with antiviral drugs (see http://www.cdc.gov/h1n1flu/clinician_pregnant.htm).

Q: Why aren't adults age 65 years and older included as a priority group for the 2009 H1N1 vaccination as they are for seasonal influenza, where they are included as part of the age-50-and-older priority group?

A: Current studies indicate that the risk of infection, hospitalization, and death from the 2009 H1N1 influenza virus among persons age 65 years and older is less than is the risk for younger age groups. Studies suggest that there is some degree of preexisting immunity to the 2009 H1N1 strains, especially among adults older than age 60 years. One possible explanation is that some adults in this age group have had previous exposure, either through infection or vaccination, to an influenza A (H1N1) virus. People age 65 years and older are included as a priority group if they live with or care for infants younger than age 6 months or are a healthcare or emergency services provider.

Q: Will H1N1 influenza vaccine be available for healthy people age 25 years and older (who are not in targeted groups)?

A: Once public health authorities at the local level determine that the H1N1 influenza vaccine demand for the 5 target groups has been met, providers will be notified that they can administer the vaccine to healthy people ages 25 through 64 years. Once demand for H1N1 influenza vaccine among younger age groups is met, vaccination should be expanded to all people age 65 and older.

Q: Once H1N1 influenza vaccine becomes available, should we stop administering seasonal influenza vaccine?

A: No. Providers should start administering seasonal influenza vaccine as soon as it is available and continue to administer it throughout influenza season, including during the winter and spring months.

Q: If a patient has received the seasonal influenza vaccine, do they need to receive the H1N1 influenza vaccine?

A: If a patient is in a risk group to receive H1N1 influenza vaccine, they should be vaccinated. Studies suggest that vaccination with season influenza vaccine will not provide protection against the 2009 H1N1 influenza virus.

Q: Will we be able to administer both the seasonal and H1N1 influenza vaccines at the same visit?

A: You can in most cases. See the points below.

• You can administer both the inactivated seasonal and the inactivated H1N1 influenza vaccines at the same visit (using separate syringes and sites) or at any time before or after each other.
   

• You can administer the inactivated seasonal and live H1N1 influenza vaccines together or at any time before or after each other.
   

• You can administer the live seasonal and inactivated H1N1 influenza vaccines together or at any time before or after each other.
   

• Administering both the live attenuated seasonal and the live attenuated H1N1 influenza vaccines at the same visit is NOT recommended because of concerns about competition between the two vaccine viruses. If you have only live vaccines for both seasonal and H1N1 influenza available, you should separate the doses of the two live vaccines by at least 4 weeks.

Q: Will there be a new Vaccine Information Statement (VIS) for the 2009 H1N1 influenza vaccine or can we use the same influenza VISs that have been issued from CDC for seasonal influenza vaccine?

A: A new VIS will be developed that pertains only to the 2009 H1N1 vaccine. You will find it posted at http://www.immunize.org/vis when it is available.

Q: In anticipation of H1N1 monovalent vaccine arriving later this fall, CDC recommends that we begin vaccinating with seasonal influenza vaccine now. Does protection from seasonal influenza vaccine decline or wane within 3 or 4 months of vaccination? Should I wait until October or November to vaccinate my elderly or medically frail patients?

A: CDC recommends that seasonal influenza vaccine be administered to all age groups as soon as it becomes available. Antibody to seasonal inactivated influenza vaccine declines in the months following vaccination. However, antibody level at a point several months after vaccination does not necessarily correlate with clinical vaccine effectiveness. There are no studies that compare vaccine effectiveness according to the month when the vaccination was given. The authors of a recent review on antibody declines among the elderly after vaccination reported, "In conclusion, we found no compelling evidence for more rapid decline of the influenza vaccine-induced antibody response in the elderly, compared with young adults, or evidence that seroprotection is lost at 4 months if it has been initially achieved after immunization." (see Skowronski et al., Rapid Decline of Influenza Vaccine-Induced Antibody in the Elderly: Is It Real, or Is It Relevant? Journal of Infectious Diseases 2008;197:490-502). In addition, there is a lack of evidence for late season outbreaks among vaccinated persons that can be attributed to waning immunity.