Baxter International Inc released results on its H5N1 pandemic flu vaccine Phase I/II trials this week and plans to move into Phase III testing.

In a prepared statement, Baxter said that the Phase I/II results show that the candidate vaccine produces a strong immune response at low doses and "and induces substantial levels of cross immunity against widely divergent H5N1 strains".

A comprehensive review of the results is under way and they will be published in a peer-reviewed journal.

The global healthcare company plans to start Phase III trials in the next few months, with results expected by the end of the year.

Phase III trials will test the vaccine on healthy European volunteers. This phase will evaluate the safety of the whole-virus candidate vaccine and assess its protective power in large groups before and during a potential pandemic.

The Baxter candidate vaccine showed a strong immune response without the help of adjuvants or additional agents used to boost responses.

The Phase III trial will also test the vaccine without adjuvant, and will be administered by intra-muscular injection.

John Oxford, professor of Virology at the Queen Mary School of Medicine in London, said the early and mid-phase results suggested that the candidate vaccine "may provide protection against divergent strains of virus, even at low dose levels without an adjuvant".

Baxter developed its candidate vaccine from a strain of H5N1 known as A/Vietnam/1203/2004 using a cell-based as opposed to an egg-based technology.

Known as "vero cell technology" the Baxter vaccine production system produces high yields more quickly than the traditional egg approach and is the first H5N1 pandemic vaccine using this manufacturing technique to undergo clinical trials.

Baxter says another advantage to using a cell-based culture is that it allows the "native virus" to be used straight away without having to modify it for growing in eggs. This speeds up vaccine production, allowing it to be available much earlier, within 12 weeks, Baxter says.

The PhaseI/II trial tested four different concentrations of the candidate vaccine, two of which were studied with and without adjuvant. In one of the non-adjuvant assisted concentrations, 7.5 micrograms of antigen, the seroprotection rate at day 42 was 76.2 per cent.

The immunity response to the A/Vietnam/1203/2004 strain also neutralized other strains like the Clade three strain A/Hong Kong/156/97, and the Clade two strain A/Indonesia/05/05.

Side-effects were similar to those reported for licensed, seasonal, egg-based flu vaccines and mostly comprised reactions at the injection site, headaches and fatigue.

Dr. Hartmut Ehrlich, vice president of Global Research and Development for Baxter"e;s BioScience business said that the preliminary trial results show a highly immunogenic vaccine with a"favorable safety profile without the need for an adjuvant to boost the immune response".

"Adjuvant can add considerable cost and may have a negative effect on tolerability. A good safety profile and cross immunity against multiple viral strains is critically important for governments considering the concept of using a vaccine before, or immediately after, a pandemic breaks out," he added.

In September last year, a study led by Michigan University, suggested that the most cost-effective and speedy way to respond to a flu pandemic in the US within the next five years is to use existing facilities to make vaccines from cell cultures.

The study compared the production costs of egg versus cell culture vaccine under pandemic conditions and found that training people to make cell culture vaccines in existing facilities was the only way that the US would be able to make enough doses quickly without huge capital investment in new facilities.

Click here for US National Institutes of Health information on Clinical Trials.

Written by: Catharine Paddock
Writer: Medical News Today