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Early clinical data indicates that two different swine flu vaccines are safe and effective, according to papers published online today in the New England Journal of Medicine.
Twenty-one days into one trial involving 240 subjects aged 18 to 64, a vaccine composed of a single antigen developed by CSL Biotherapies, a flu shot manufacturer based in Parkville, Australia, appears to significantly boost antibody levels in more than 93% of people at both normal and double doses. No serious adverse effects have yet been found, the authors report.
In another three-week trial of 175 adults aged 18 to 50 run by clinicians at the University of Leicester, UK, Novartis’ adjuvanted swine flu vaccine yielded protective levels in at least 80% of participants at half the normal dose and more than 90% of subjects given a full dose. Many people experienced pain and muscle ache, and two participants became feverish. The study confirms early reports of success announced last week.
Neither flu trial included a proper control group. So it’s impossible to rule out the possibility that subclinical exposure to the virus jacked up immune systems in the trial from Australia, where the pandemic has recently been circulating, notes Kathleen Neuzil, an infectious disease expert at the University of Washington School of Medicine in Seattle, in an accompanying editorial. Similarly, without a non-adjuvanted group in the British trial, the importance of the adjuvant — designed to enhance the effectiveness of the flu shot — remains uncertain, she writes.
A third NEJM report published today by the US Centers for Disease Control and Prevention inspected levels of pre-existing immunity to the widely circulating H1N1 virus. Using a test called a microneutralization assay, which determines whether blood serum samples contain antibodies that block viral infection, the CDC researchers found that around 1 in 3 older adults had significant antibodies against swine flu, but less than 1 in 20 people under 30 harboured similar protection.
Previous vaccination against seasonal influenza had little effect, leading the CDC scientists to conclude that the “optimal protection against 2009 H1N1 in persons of all ages will be achieved with the development of a strain-specific pandemic vaccine.” Similar results were published in May in the CDC’s Morbidity and Mortality Weekly Report.