A universal influenza vaccine — so-called because it could potentially provide protection from all flu strains for decades — may become a reality because of research led by scientists from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
The prime-boost approach opens a new door to vaccinations for influenza that would be similar to vaccination against such diseases as hepatitis, where we vaccinate early in life and then boost immunity through occasional, additional inoculations in adulthood. In experiments with mice, ferrets and monkeys, the investigators used a two-step immunization approach to elicit infection-fighting antibodies that attacked a diverse array of influenza virus strains. Current flu vaccines do not generate such broadly neutralizing antibodies, so they must be re-formulated annually to match the predominant virus strains circulating each year. A durable and effective universal influenza vaccine would have enormous ramifications for the control of influenza, a disease that claims an estimated 250,000 to 500,000 lives annually, including an average of 36,000 in the United States.
Vaccination with plasmid DNA encoding H1N1 influenza hemagglutinin (HA) and boosting with seasonal vaccine or replication-defective adenovirus 5 (rAd5) vector encoding HA stimulated the production of broadly neutralizing influenza antibodies
This prime-boost vaccine stimulated an immune response to the stem of the lollipop-shaped hemagglutinin of influenza virus. Unlike HA’s head—which mutates readily, allowing the virus to become unrecognizable to antibodies—the stem varies relatively little from strain to strain. In principle, Dr. Nabel explains, antibodies generated against the stem of HA should be able to recognize and neutralize multiple flu strains.
Moreover, although the prime-boost vaccines were both made from H1 subtypes of influenza A virus, the antibodies they generated neutralized other influenza subtypes, including H5N1 (avian influenza) virus. This indicates that a prime-boost strategy potentially could confer immunity to many or all subtypes of influenza A, says Dr. Nabel.
In another set of experiments, the scientists measured how well the prime-boost vaccine protected mice and ferrets from infection with deadly levels of flu virus. Three weeks after receiving the boost, 20 mice were exposed to high levels of 1934 flu virus, and 80 percent survived. Mice receiving DNA only, seasonal flu vaccine only or a sham prime-boost vaccine all died.
The researchers saw similar results when they tested several prime-boost combinations in ferrets, which are considered a good animal model for predicting flu vaccine efficacy in humans. All four ferrets that received a DNA prime-seasonal boost were protected from infection with a 2007 virus strain, while all six ferrets that received the DNA prime-cold virus boost combination were protected from the 1934 influenza virus.
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