Today’s much awaited meeting billed as “urgent” of the Advisory Committee on Immunization Practices (ACIP) recommended that the U.S. government launch a vaccine program against the 2009 H1N1 influenza virus.
The 15-member ACIP, which advises the Department of Health and Human Services (HHS), said that because there likely will be a limited amount of vaccine at the start of the traditional influenza season this fall, five groups of people should be put at the head of the line.
- In addition to people who have underlying conditions that put them at a greater risk of severe disease from the swine flu virus, the other top priority groups include:
- Pregnant women,
- Everyone between 6 months and 24 years of age
- People who live with infants under 6 months of age (who cannot be vaccinated themselves)
- Healthcare workers and emergency personnel.
Dosage and Required Number of Shots Unsure
Estimates suggest that this initial target population includes up to 159 million people. HHS currently predicts that it will at most have 160 million doses in October. Each dose will contain 15 micrograms of product, and that may not be enough vaccine if, as many expect, two doses are needed to establish a protective immune response (this reduces the amount down to 80 million possible doses). Anne Schuchat, director of the national center for immunization and respiratory diseases at the U.S. Centers for Disease Control and Prevention, a division of HHS, stressed that many questions still remain about the demand for the vaccine, as well as the ultimate dose needed per person.
Further complicating matters, vaccine may be ready and approved by the Food and Drug Administration before clinical trials that test different doses of the vaccine are completed, she said. “The clinical trials will give us information that’s helpful, but there are other decisions to be made going forward” that will need to take circumstances into account, said Schuchat. “The National Biodefense Science Board, which advises the HHS preparedness group, has actually recommended going forward without waiting for the clinical trials—at least in some amount of vaccine. It’s a serious question we’re deliberating on right now.”
Plan B if Supply is Limited
Given the uncertainties about supply and demand, Schuchat noted that ACIP also came up with a “just-in-case prioritization group” of about 41 million people. That group would restrict vaccine availability to some healthcare workers and emergency personnel, and the age cut off would drop to 4; those under 18 with underlying risk factors also would be eligible.
The word “adjuvant” comes from the Latin adjuvare, meaning “to help.” Adjuvants are substances that enhance the ability of an antigen to stimulate an immune response in the body. The addition of adjuvants helps to boost the potency of the antigen and stimulate the immune system in an effective manner.
The current recommendations do not tackle the thorny issue of adjuvants, which may be needed to boost immunity from the viral antigens in the vaccine or to stretch the amount of product that can be made from a limited amount of antigen. Safety issues about the use of adjuvants may delay the approval of vaccines which contain them, said Schuchat. “We are evaluating the need for adjuvants, but our working plans right now are that we’re expecting not to need them.”
Vaccine manufacturers also intend to use thimerosal in some of the vaccines. This mercury containing preservative was removed from many other vaccines after public concern grew about potential harm to children. Schuchat said thimerosal-free vaccine will be available. But she also emphasized that ACIP and CDC generally do “not express a preference for thimerosal-free, based on the science about that component.”
More Canadian Pigs Catch New Flu Virus
According to the Ministry of Agriculture, Fisheries and Food of Quebec (MAPAQ), the 2009 H1N1 influenza virus infected a herd of pigs in this Canadian province. This is only the third hog farm known to have become infected with the virus that is causing the swine flu pandemic in humans.