WASHINGTON - Most healthy adults will need only one vaccine shot rather than two to protect against the 2009 H1N1 swine-origin influenza A virus, and the effect of the vaccine appears to kick in quicker than first thought, according to early results of clinical trials from Australian firm CSL Ltd. and the National Institute of Allergy and Infections Diseases (NIAID).
Those results could mean that the limited vaccine supply, with only 45 million doses expected to be made available in the U.S. by mid-October because of poorer-than-expected yields from growing the virus in chicken eggs, could be stretched further than if two shots were needed.
It also means it may be unnecessary to use adjuvants in the H1N1 vaccine, NIAID Director Anthony Fauci told BioWorld Today.
Given the positive study results, he said, the government has no plans to use adjuvants with the H1N1 vaccine. Nonetheless, Fauci added, the government still plans to test a vaccine with adjuvants in healthy adults, with a trial expected to start Monday.
Preliminary results of CSL's randomized, observer-blind, parallel-group trial of its inactivated, split-virus vaccine in 240 healthy adults 18 to 64 years conducted in Australia showed that a single 15-mcg dose produced a robust immune response in 96.7 percent of participants after 21 days. A dose of 30 mcg showed a 93.3 percent response at 21 days.
Results of the government's independent studies of the vaccine in healthy adults, which got under way on Aug. 7, "corroborate and reinforce" CSL's results, Fauci told reporters Friday during a briefing.
In addition, he said, the government's early results also showed that the vaccine candidates may take effect within eight to 10 days, quicker than expected.
"This is very good news for the vaccination program, both with regard to the supply of vaccine as well as to its potential efficacy," Fauci said.
NIAID is overseeing several government-funded trials run by a network of medical centers testing one or two shots of 15-mcg or 30-mcg doses of investigational unadjuvanted, inactivated H1N1 vaccines from Melbourne, Australia-based CSL and Paris-based Sanofi-Aventis Group.
More than 2,800 people are participating in the ongoing NIAID trials.
The government's studies of the vaccines in children started about two weeks after the adult trials, with trials in pregnant women getting under way just last week.
Fauci said early results from the children studies will be available in less than two weeks, with the pregnant women results available later.
Sanofi and CSL, along with the other U.S. licensed seasonal flu vaccine makers, London-based GlaxoSmithKline plc, Basel, Switzerland-based Novartis AG and Gaithersburg, Md.-based Medimmune Inc., also are conducting clinical trials of their H1N1 candidate vaccines independent of the government.
Results from the NIAID studies showed that among healthy adults who received a single 15-mcg dose of the Sanofi's vaccine, a robust immune response was measured in 96 percent of adults 18 to 64 years and in 56 percent of adults 65 or older, Fauci said.
Among healthy adults who received a single 15-mcg dose of CSL's vaccine there was a measured response in 80 percent of adults 18 to 64 years and 60 percent of those 65 and older.
Although there were lower responses in the elderly group, Fauci said they were "essentially right on the money" and "in the ballpark" of what are normally seen with seasonal flu vaccines.
The elderly, he noted, generally have less of a response to flu vaccines than younger populations.
Only the government is studying H1N1 vaccine candidates in the 65 and older age group, Fauci told BioWorld Today.
Officials noted that the slight discrepancies between the Sanofi and CSL vaccines in the government's trials may be due to technical differences in the preliminary measurement of the amounts of antigen in the doses used in the clinical trial lots and the relatively limited numbers of samples studied to date.
Fauci added that it also may be due to the fact that the government study results are drawn from a very early time point after immunization.
There have been nearly 600 deaths from the H1N1 swine flu in the U.S. since last spring, with more than 9,000 people hospitalized, according to the Centers for Disease Control and Prevention.
The 2009-10 flu season already is under way, with the H1N1 virus never actually going away over the summer, said Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases.
The CDC has attributed about 98 percent of the current flu-like activity to the H1N1 virus, she said.
"The levels of flu activity that we are seeing right now in September are extremely unusual for this time of year," Schuchat told reporters.
Fauci said flu shots given now should provide protection for up to a year.
CDC's Swine Flu Front Man Goes to ABC
Terrorism and emergency preparedness expert Richard Besser, the person who led the CDC's response to the 2009 H1N1 flu during the early days of the outbreak last spring, left the agency to join ABC as a senior health and medical editor to provide commentary for all news broadcasts, along side the Disney-owned network's longtime medical editor Tim Johnson.
Besser, the former director of the CDC's Coordinating Office for Terrorism Preparedness and Emergency Response, led the agency as acting director during the first five months of the Obama administration until former New York City health commissioner Thomas Frieden took the helm in June. (See BioWorld Today, May 18, 2009.)
He appeared almost ubiquitously on U.S. morning and evening news broadcasts and other television and radio programs from April to June providing updates about the spread of the swine flu.
Besser had served at the CDC since 1991, except for a five-year stint from 1993 to 1998, when he headed the University of California at San Diego's pediatric residency department.