By Tan Ee Lyn
HONG KONG, March 5 (Reuters) - Top virologists called on Monday for a greater effort in developing effective vaccines against a potential flu pandemic and warned that all contingency plans would be in vain without them.
While the H5N1 bird flu virus is widely seen as a likely candidate for the next pandemic, the experts cautioned the world against losing sight of other flu viruses.
Flu vaccines thus should be "broad-based" and protect against as many virus strains as possible, they said.
"If you solve the problem of vaccines, our pandemic preparedness planning will be much more realistic," Albert Osterhaus, virology professor at the Erasmus Medical Centre in Rotterdam, told Reuters.
"If we are not prepared in terms of antivirals and vaccines, millions of people are going to die," he said.
Viruses mutate all the time and any vaccine against a pandemic flu virus can only be designed after the disaster has occurred.
But the pharmaceutical industry is already designing "pre-pandemic H5N1 vaccines" in the hope they can offer some form of protection before a pandemic vaccine is ready, a process that can take up to six months.
Osterhaus, who is in Hong Kong for a medical conference, said more work needed to be done to shorten this process.
"We have to find a strategy where we can rapidly have a vaccine in two, three months (of a pandemic)," he said.
"In principle, we have the technology, but we don’t have the capacity. To date, the world production of flu vaccine is 400 million doses, but we are over 6 billion people, and probably we have to shoot (inject) twice."
The threat of a pandemic has spurred new projects to make vaccines cheaper and more effective.
Osterhaus’s laboratory is trying to design vaccines that use less antigen and more adjuvants.
Antigens are substances that stimulate the production of antibodies when they are introduced into the body, such as toxins, viruses and bacteria. But there simply would not be enough antigen in the event of any flu pandemic.
"We have to use less of the antigen in the vaccine so we can vaccinate more people. We need more antigen, more than 10 times more, so the key message is we need to go with adjuvants," said Osterhaus.
Adjuvants are additives that enhance the effect of drugs or vaccines.
"We are testing different adjuvant systems, to see which is the best, gives the broadest, longest-lasting protection, and with the least amount of antigen," Osterhaus said.
The search for a viable pandemic vaccine is also brewing in the laboratory of leading HIV/AIDS drug scientist David Ho.
Using DNA technology, Ho has constructed a broad-spectrum vaccine, which he hopes would be effective against various strains of H5N1. Initial tests on mice showed the vaccine was effective against the H5N1 strain in Vietnam.
"These results are still some time away from getting into human testing. This is a very slow process," cautioned Ho, who is in Hong Kong to attend another medical conference organised by Massachusetts General Hospital, University of Hong Kong and the Nature publishing group.
Both Ho and Osterhaus stressed the need to move away from using chicken eggs in the production of flu vaccines.
"In a pandemic, you need much more vaccine. But chickens only lay one egg a day. You can’t order them to lay two or three a day," Osterhaus said.