New flu vaccines offer promise, challenges.
And new vaccines are desperately needed: Current seasonal vaccines are only 30%-50% effective in older adults, and candidate vaccines for pandemics "are poorly immunogenic in clinical studies," Dr. Bright told attendees.
Current influenza vaccines may be safe and immunogenic, but they are highly vulnerable to antigenic drift and shift, which compromise efficacy and require reformulation and repeated immunization.
In addition, vaccine development is costly, complicated, and time consuming. As the recent H1N1 influenza outbreak demonstrates, the conventional production process is poorly equipped to respond to a pandemic, Dr. Bright said.
He discussed three promising types of influenza vaccines: live attenuated influenza viruses (LAIV), recombinant viruslike particles (VLP), and plant-based production of vaccines. Each holds promise, but all involve significant challenges, including safety, immunogenicity, scalability, and regulatory issues.
LAIV: Innovative Yet Decades Old
LAIVs have been used to combat seasonal influenza for decades in some parts of the world, including the United States and Russia, but Dr. Bright nevertheless characterized them as innovative. They have yet to be widely accepted or distributed, despite a strong safety record and low cost. In fact, he said, LAIV is the lowest-cost influenza vaccine available today. It's easy to produce and purify; it has a broad immune response, including some mucosal and cellular immunity; and it is efficacious in naive populations, he said.
There are challenges, however. LAIV "doesn't follow the known, established correlates of immunity," which can lead to regulatory and licensing hurdles.
Moreover, LAIVs are less effective in nonnaive adults, and there are current limitations on their use in children and some high-risk groups. But, he added, some of those limitations are based on "unfounded fears of the risk of reassortment."
Over the last few years, LAIV technology has expanded into development of both seasonal and pandemic vaccines.
VLP: Dealing With Vectors
VLP vaccines, with many varieties in early-stage development, show promise of being both low cost and high yield, with a rapid (12-week) production cycle, he said. Dr. Bright explained that although VLPs contain multiple influenza proteins to resemble virions, they contain no genetic material, and therefore they do not replicate or cause infection.
Safety is an issue because all VLPs "rely on some sort of vector." The challenge is to remove--or demonstrate the safety of--the residual vectors, Dr. Bright said, noting that such concerns could lead to regulatory challenges.
Plant-Based Vaccines: Speedy Development
Plant-based vaccines have been advancing steadily since 2000, he reported. Such vaccines can be produced very rapidly, at about 8 weeks from sequencing to release. New approaches to plant-based expression create high yields with low production costs. Moreover, he said, the approach is "suitable for mixing and matching constantly emerging strains."
Safety appears to be less of a concern than it is for VLPs, according to Dr. Bright, because plant-based vaccines are free of animal cells, microbial pathogens, and animal viruses. But "there are many things we don't know about the safety of plant-based proteins," he said.
Disclosures: Dr. Bright disclosed receiving stock as part of a management position in 2006 from Novavax Inc.
ARTICLES BY ROXANNA GUILFORD-BLAKE
FROM THE INTERNATIONAL CONFERENCE ON EMERGING INFECTIOUS DISEASES
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|Title Annotation:||INFECTIOUS DISEASES|
|Publication:||Internal Medicine News|
|Date:||Aug 1, 2010|
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