pandemic influenza




Vaccination is considered the best preventive measure against influenza. But, because of continuous changes in the genes of flu viruses, vaccines must be “matched” to strains in circulation to provoke good immunity. Vaccine is currently produced through a time-consuming process, using chicken eggs, with a lead time of four months or more. Since a vaccine cannot be produced for a flu pandemic until that strain emerges, a matched vaccine would not be available for initial global pandemic response.28 Recent U.S. pandemic planning efforts have focused on (1) expanding domestic capacity to mass-produce flu vaccine in the near term; (2) developing approaches to speed up and “stretch” existing production capacity, such as through the use of adjuvants, vaccine additives that boost the immune response so that a lower virus dose is effective; and (3) developing better approaches for flu vaccine production in the future. Although recent progress has been made to improve domestic production capacity, a vaccine for the current H1N1 pandemic will still be made using the egg-based process, with its significant lag time.

U.S. efforts to make a vaccine against H1N1 pandemic flu are underway. Federal officials have said that there are three key decision points in developing and using vaccines in response to a flu pandemic: (1) to develop prototype or “seed strain” viruses with the proper characteristics to produce a safe and effective vaccine, to develop a prototype vaccine(s), and to conduct clinical trials on the prototype(s); (2) to purchase and mass-produce large amounts of a promising vaccine; and (3) to administer the vaccine widely, that is, to conduct a mass-vaccination campaign. These decision points are presented, in a timeline of the U.S. pandemic flu vaccine strategy, in Figure 2. Each of these decision points is distinct. The first step has begun, and the second is partly underway. Officials note that it is important to begin production of a pandemic vaccine at this time, but that a decision to administer the vaccine, once it were available, would be made separately, based on conditions at the time.

Figure 2 also shows that there may be a second wave of transmission of H1N1 flu in the United States in the fall, which could occur between peaks of seasonal and pandemic flu activity in the Southern Hemisphere (i.e., during summer in the United States), and seasonal flu activity in the Northern Hemisphere (i.e., during our upcoming winter). The figure illustrates the three types of activities corresponding to the decision points noted earlier: (1) vaccine development; (2) vaccine manufacturing; and (3) vaccine distribution and administration. Each type of activity involves several distinct steps, some of which must be carried out sequentially, and others of which could be carried out simultaneously. The figure also shows the overlap between the production of seasonal flu vaccine for the Northern Hemisphere, and production of a vaccine against the pandemic strain.

vaccine development

Figure 2. Proposed Timeline for H1N1 Vaccine Development, Manufacturing, and Possible Distribution and Administration

On May 22, HHS Secretary Kathleen Sebelius announced that approximately $1 billion in existing funds were to be used for clinical trials on H1N1 prototype vaccines, to be conducted over the summer, and for commercial-scale production of two potential vaccine ingredients for the pre-pandemic influenza stockpile.30 Also in May 2009, HHS issued new orders on existing contracts with several flu vaccine manufacturers to produce a bulk supply of vaccine antigen and adjuvant and to produce pilot (also called investigational) lots of a 2009 H1N1 vaccine. Most of this would be stored in bulk, and a small amount would be prepared as vaccine for use in clinical studies to evaluate vaccine safety and the dosage required for a protective effect. This research is to include studies with adjuvant to determine its safety and the effect it would have on the immune system’s response. These efforts are led by the HHS Biomedical Advanced Research and Development Authority (BARDA), in coordination with FDA, CDC, and other HHS agencies.

If federal officials decide to request and purchase enough vaccine against H1N1 flu to support a mass vaccination campaign, sufficient doses would not be available until the fall of 2009, because of the timing and capacity limitations discussed earlier. Financing for this purchase would also have to be established. President Obama has requested substantial funding and budget transfer authority in pending FY2009 supplemental appropriations, which could support this objective. (See the section “Emergency Supplemental Appropriations for FY2009”.)

If federal officials also decide to launch a mass vaccination campaign, several key decisions would have to be made. It is not yet clear whether such a campaign would use the private-sector distribution mechanism that delivers seasonal flu vaccine each year, or the public sector mechanism that CDC, state, and local officials have practiced to distribute countermeasures from the Strategic National Stockpile. This key decision would affect several others, including how to prioritize vaccine (which would become available in phases) to those most in need, and how to track who has received the vaccine, and any adverse events that occur in those who receive it.

Source :
The 2009 Influenza Pandemic: An Overview
Sarah A. Lister Specialist in Public Health and Epidemiology
C. Stephen Redhead Specialist in Health Policy
June 12, 2009

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