Sparse details of the world's first clinical trial of a swine flu vaccine emerged Tuesday, with Chinese manufacturer Sinovac reporting that a single dose of its vaccine produces a good immune response.
But the company did not reveal key details, including the size of the dose or the formulation of the vaccine, information that would be needed to determine whether other vaccine makers could expect to see similar results.
Authorities are anxious to learn more about the trial, conducted in 1,641 people aged three years and older in China.
"WHO looks forward to reviewing as soon as possible detailed immunogenicity results from the Sinovac clinical trial," Dr. Marie-Paule Kieny, head of the World Health Organization's vaccine research initiative, said via email.
"They can bring precious early information on what H1N1 vaccine formulations seem to be effective."
The Sinovac release said the pandemic vaccine was well tolerated by participants with no signs of serious side-effects. The adverse reactions that were reported were similar to those seen with seasonal flu vaccine administration, it said, with a sore arm being the most common complaint.
"As demonstrated in the clinical trial of our H1N1 vaccine, we can confirm the immunization schedule and dosage, which can provide the scientific reference to the state government to establish the inoculation strategy of H1N1 vaccine," Sinovac president and CEO Weidong Yin said in the release.
"Sinovac plans to complete the summary report as soon as possible and fully evaluate the safety and immunogenicity of the H1N1 vaccine."
The director of the U.S. National Institute of Allergy and Infectious Diseases said news that a single dose might be adequate to protect against the virus is a hopeful sign, but cautioned against drawing any conclusions until more is known about the trial and its findings.
"This is encouraging news if in fact the product that they used is similar to the product that we're using, number 1, and number 2, if the data backs up the statement that they gave to the press," Dr. Anthony Fauci said from Bethesda, Md.
He said Sinovac should share its data.
"I'd like to see the data. I'd like to know . . . did they really have an adequate immune response to just one dose? If so, that's great news, I'm glad to hear that. But we need to see the data."
A flu vaccine expert at the University of Rochester, N.Y., echoed Fauci's caution, but said it is plausible that one shot may suffice for at least a portion of the population.
"I think at a certain age you're going to respond to a single dose probably pretty well," said Dr. John Treanor, chief of infectious diseases at the University of Rochester Medical Center.
"I don't know what that age cut-off is. Who knows? Maybe everybody will respond to a single dose. That's one of the big unanswered questions right now."
An earlier release from the company said Sinovac would study several dose sizes, ranging from five to 30 micrograms.
Seasonal flu shots contain 15 micrograms for each virus type they protect against. But it could not be assumed that a standard dose would be sufficient to protect against a new virus, one to which most people under 55 or 60 have little or no immunity.
Sinovac had also announced it would study vaccines made in different ways, one using whole viruses and the other using viruses that had been broken down or split. (In both cases the viruses are killed, or in the language of vaccine makers, inactivated.)
The former process is thought to provoke a stronger immune response, but also triggers more reactions in recipients. As a consequence, most major vaccine manufacturers have switched to a split virus process.
If the formulation that worked for Sinovac was whole virus vaccine, the results may not translate for other vaccine makers, Fauci said.
"You can't say all of a sudden 'We're going to start doing whole virus.' Sorry, the train left the station," he said.
Likewise it will be important to know whether the vaccine contained an adjuvant, a compound that boosts the immune system's response to vaccine, allowing smaller doses to be used. Some manufacturers are planning to make adjuvanted pandemic vaccine. But others, like Sanofi Pasteur, will not.
Canada intends to use adjuvanted vaccine produced in Ste-Foy, Que., by GlaxoSmithKline.
Dr. David Butler-Jones, head of the Public Health Agency of Canada, has said data GSK generated while studying its experimental vaccine against H5N1 avian flu suggests one dose of adjuvanted vaccine may be adequate to protect most people in Canada against swine flu.