Chasing a big market opportunity that recently tripped up another vaccine developer, Bavarian Nordic reports that a single shot of its universal respiratory syncytial virus (RSV) candidate can elicit a significant immune response shortly after vaccination.
The results come from a phase 2 test of Bavarian Nordic's vaccine candidate, which targets more RSV proteins than any other candidate tested so far.
The study enrolled 421 subjects aged 55 or older at 12 sites across the U.S. One week after vaccination, most participants experienced 5- to 10-fold T-cell responses to all five RSV proteins included in BN's vaccine, compared with placebo. Participants also saw 2- to 4-fold antibody responses after two weeks. At the three-month mark, the vaccine response was still significantly better than placebo, the company reported.
In addition to targeting a greater number of RSV proteins, BN's vaccine candidate was designed to elicit a mucosal response at the site of infection.
“Our vaccine was designed to stimulate immune responses which are very broad, but are also mimicking the antibodies and T-cell responses that are generated when you’re naturally exposed to RSV, which should translate into protection,” Bavarian Nordic president and CEO Paul Chaplin said during a press call Tuesday.
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Investigators are still analyzing the blood samples taken six months after vaccination and plan to track the subjects for another six months.
Most adults recover from RSV infections with only mild symptoms, but the virus can cause severe respiratory illnesses in infants and in the elderly. While RSV treatments for infants are available, there aren’t any options for elderly adults, who make up about 78% of the 14,000 RSV-related deaths each year.
Market watchers have said an effective vaccine could be worth $6 billion per year or more, making RSV one of the last large commercial opportunities for vaccine developers. The World Health Organization has designated RSV as a high-priority target for vaccine development because there are no approved products to protect against the respiratory virus.
Novavax and MedImmune each have RSV vaccine candidates that have earned fast-track designations at the FDA. After failing a large-scale phase 3 study because of what the company called a sluggish RSV season, Novavax recently restarted its RSV F-protein recombinant vaccine program from phase 2, this time outside of an RSV season.
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Taking lessons from that trial failure, Chaplin on Tuesday said BN doesn’t want to conduct its entire phase 3 trial over just one season. While scientists are still testing blood samples taken at the phase 2 study's six-month mark, the Danish company plans to examine the duration of immunity moving forward.
To do that, BN will re-enroll some subjects who received a single vaccination, revaccinate them later this year, and follow them for another RSV season to examine one-year immune responses. That data will help BN decide whether its candidate is a seasonal vaccine, like the flu shot, or one with a longer duration of protection. That knowledge might guide BN in planning for a phase 3 currently expected to start in 2019 or 2020.