Experts weigh new H5N1 vaccine strategies

Feb 3, 2009 (CIDRAP News) – At an Infectious Diseases Society of America (IDSA) symposium in Washington, DC, today on seasonal and pandemic influenza, a group of experts fielded questions from reporters on some of the new trends and emerging issues, including prepandemic strategies for H5N1 avian influenza vaccines, now that some countries are stockpiling them.

Keiji Fukuda, MD, MPH, coordinator of the World Health Organization's (WHO's) global influenza program, told reporters that experts don't really know what virus will spark the next global pandemic, but given the persistent and lethal nature of the H5N1 virus, the WHO has received pledges from pharmaceutical manufacturers to develop a 150 million dose international vaccine stockpile. He said the stockpile is intended to stop or slow a pandemic if the outbreak is detected early enough.

The existence of individual-country H5N1 vaccine stockpiles and plans for a WHO global stockpile have raised complex questions about potential uses for the vaccine during the prepandemic period, Fukuda said.

Some countries are weighing what to do with the vaccines, especially since some doses are set to expire. Global health officials are considering other options, such as vaccinating people in high-risk countries such as China, Indonesia, or Vietnam or perhaps adding the antigen to seasonal flu vaccines as a priming strategy.

The United States, for example, has so far stockpiled about 26 million H5N1 vaccine doses, though some has already expired or is about to expire, according to a Sep 2008 report on US pandemic vaccine policy from the Congressional Budget Office (CBO). The HHS has launched studies to determine how long stockpiled vaccines remain safe and effective, but in the meanwhile it assumes a 2-year shelf life.

The United Kingdom has stockpiled 3 million doses of H5N1 vaccine. Several countries have announced stockpiling plans, including France, Ireland, Italy, and Austria, according to the CBO report. Other countries such as Japan are in the midst of clinical trials to produce their own H5N1 vaccines.

During a Jan 28 US Department of Health and Human Services (HHS) webcast update on the status of the nation's pandemic preparedness, Robin Robinson, director of the HHS Biomedical Advanced Research and Development Authority (BARDA), said the influenza community this year will discuss the possibility of adding H5N1 antigen to the seasonal flu vaccine. "The benefit is that it could provide some priming . . . the counter side is that we don't know yet what this H5N1 vaccine would be like in millions of people in a seasonal situation," he said.

Robinson added that health officials are highly sensitive of the 1976 experience with the swine flu immunization, when some cases of Guillian-Barre syndrome were associated with the vaccine.

Fukuda said the WHO's Strategic Advisory Group of Experts (SAGE) on immunization will meet in early April to discuss potential uses of H5N1 vaccine during the prepandemic period.

In November 2008, the WHO established a SAGE working group to focus on H5N1 vaccine issues. According to the Jan 9 issue of the WHO Weekly Epidemiological Record, the working group said it would address:

  • Use of the H5N1 vaccine during the prepandemic period to protect people in high-risk jobs, such as cullers, essential workers, and the public
  • Priming and immunization strategies for essential workers and the general public
  • Recommendations to the WHO and other groups on what to do with H5N1 doses that are about to expire
  • Possible changes to the projected size of the WHO's H5N1 vaccine stockpile

"It's likely that different countries will look at this issue differently. This is quite an important pivotal discussion," Fukuda said. Though the WHO's stockpile is still in a virtual state, made up of pledges from pharmaceutical companies, Fukuda said countries that have real stockpiles are facing imminent issues about what to do with expiring H5N1 vaccine. "This will be a country-by-country decision," he said.

Arnold Monto, MD, an influenza epidemiologist at the University of Michigan, told reporters that some experts began discussing the possibility of adding H5N1 antigen to the seasonal flu vaccine a few years ago, but he said some elements of the vaccine have changed since then.

For example, he said more companies are developing H5N1 vaccines that use adjuvants, or immune-boosting chemicals, as a dose-sparing strategy, which might complicate combining the H5N1 component with the seasonal flu vaccine. Also, he said unlike single-dose seasonal flu vaccines, the H5N1 vaccine is given in two doses.

Though Monto predicted that discussions will continue on the appropriate use of the H5N1 vaccine, he said new uses for the vaccine won't happen anytime soon.

Among other possibilities for the H5N1 vaccine, pharmaceutical companies might some day market the product to the public, Monto said, adding that if the H5N1 virus ever turns up in North American birds, Americans might demand the vaccine.

At today's press conference, influenza experts also provided updates on other influenza topics:

  • The US flu season has been relatively mild, said Nancy Cox, PhD, director of the influenza division at the Centers for Disease Control and Prevention (CDC). She said she expects flu activity to increase over the coming weeks as the season peaks. "Remember, it's not too late to get the seasonal flu vaccine," she said.
  • Among several suggestions to improve the seasonal flu vaccine, experts are considering adding a second influenza B strain to the vaccine to help solve the problem of deciding which strain to add, said Monto. Early returns this season suggest that Victoria strains are more common, though this season's vaccine contains the Yamagata strain.
  • Much more work is needed on bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), that cause influenza complications, said Andrew Pavia, MD, chair of the IDSA National and Global Public Health Committee. Pavia also said more work is needed to develop better treatments and determine who is at increased risk of dying from the complications.
  • A road map for influenza research is being fleshed out by the Wellcome Trust, an independent medical research funding charity based in London, said Frederick Hayden, MD, an influenza expert at the University of Virginia School of Medicine in Charlottesville. He said the process will help identify research gaps.

See also:

WHO SAGE on Immunization Web site

Background information on WHO SAGE H5N1 vaccine working group
http://www.who.int/immunization/sage/sage_wg_H5N1_oct08/en/index.html

May 16, 2008, CIDRAP News story "Launch of WHO H5N1 vaccine stockpile still awaited"

Jan 9 WHO Weekly Epidemiological Record

Jan 16 CIDRAP News story "Experts consider 4-strain flu vaccine to fight B viruses"

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