A single swine flu dose enough for protection: Data

A single standard dose of vaccine may be enough to protect most people against swine flu, according to preliminary research in China that suggests twice as many people as projected could receive the pandemic shot.

An experimental vaccine gave a protective immune response in 85 per cent of adults who received an initial dose at the same strength used in seasonal flu shots, Xiaofeng Liang, director of the national immunisation programme at the Chinese Center for Disease Control and Prevention, told a meeting in Beijing today.

The results provide the earliest indication of the formula that Sanofi-Aventis SA, GlaxoSmithKline Plc and other drugmakers may need to use in making hundreds of millions of doses of vaccine to fight the new H1N1 influenza strain. Authorities in the US and UK have predicted two shots would probably be needed, a regimen that would reduce the number of people who could be protected before the northern hemisphere’s winter. “This is very promising information, and if we are able to get an immunogenic response with one dose as opposed to two doses, this would be a very significant change in our expectations,” Keiji Fukuda, the World Health Organistion’s assistant director-general of health security and environment, told the meeting. “Up until now, most of us have been thinking that two doses would be necessary to develop an immunogenic response.” Health officials are awaiting more data from China, as well as studies overseas, to confirm the results. More results will become available in mid September, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, told reporters Friday.

‘Waiting anxiously’
“We are waiting anxiously for the immunogenicity data to get a better handle on how well one dose and two doses might work,” Ira Longini, a University of Washington statistician who advises the US government on flu, told the Beijing meeting today. “It may turn out that one is sufficient. Then we could obviously get a lot more vaccine into people much faster. It could essentially double the supply.”

The China data are based on interim results from two of the 10 companies conducting studies in the country on vaccines to fight the new H1N1 virus.

Chinese studies
Several vaccine types and strengths are being tested in seven provinces of China across four age groups in studies supervised by the country’s CDC, he said.

The trials are assessing the safety and effectiveness of at least three different vaccine strengths in single or two-dose programs, and involving inoculations based on whole and split viral particles, he said. The studies also looked at whether an aluminum-based chemical called an adjuvant boosted the body’s ability to produce infection-fighting antibodies.

Vaccines produced annually for seasonal flu combine 15 micrograms of antigen — the protein that prompts the production of antibodies — from each of the three most common influenza strains.

Liang said that a similar dose may be needed to protect most people against the pandemic strain.

“Adolescents and adults had a better response than children and the elderly,” he said. “Taking into consideration the safety, immunogenicity and the cost, a 15-microgram, split vaccine without adjuvant could be used for future vaccination.”

No data is available in children younger than 3, Liang said. A final decision on whether one or two doses will be required to provide protection across all age groups in China won’t be taken until all the data has been collected and analysed, he said.

Sinovac Biotech Co, a Beijing-based company created in 2001 to make immunisations for hepatitis, said last week that its H1N1 vaccine was safe and protected people against the pandemic virus after a single shot.