Preparing fo a possible pandemic presents difficulties, writes Dick Ahlstrom, Science Editor.
Irish health officials are preparing for the possibility of an influenza pandemic even though a human pandemic caused by a virus that has already killed at least 60 people in Asia might never arise.
There is no way to know whether the H5N1 avian flu strain that has spread to Turkey and Romania from the Far East will ever cause widespread human infection, states the chairman of the Government's expert committee on the influenza pandemic, Prof William Hall.
"I am not trying to minimise the dangers. What we have to do is prepare as well as possible," says Prof Hall who is director of the National Virus Reference Laboratory at UCD and a consultant microbiologist at St Vincent's hospital.
The committee has already asked the Department of Health for a million doses of a powerful antiviral drug that can suppress flu infection; 600,000 doses are already available with the remainder arriving early next year.
The committee also wants the department to procure vaccines against the H5N1 virus for healthcare workers. "We have also asked the department about making arrangements with vaccine producers to get us on the waiting list for any new candidate vaccine that might come along."
This shows however just how uncertain things are when it comes to preparing for an influenza outbreak. The vaccine makers need examples of any strain that can cross-infect humans but no such strain has yet arisen. The illness currently remains one only affecting birds.
It has emerged however that one candidate vaccine that might be useful against the H5N1 flu strain does not produce strong immunity when given only once.
The current vaccine against this strain would need a double dose to protect against infection, Prof Hall says. This means much more vaccine would be required should a human outbreak of H5N1 occur.
The preparations must continue given the possibility that this avian virus could make a jump into humans and spread internationally, Prof Hall argues. Avian flu viruses usually only infect birds and pigs but spontaneous changes in the virus as it passes through a host can suddenly make it infectious for humans.
Two different flu viruses infecting a single host, be it bird, pig or human, can also recombine, delivering a virus that is at once more infectious, more dangerous and new enough that there will be little natural immunity against it.
This makes the waiting game very difficult, not knowing what the virus is going to do next. The H5N1 strain now threatening to mutate and make the jump into humans has killed more than half of those who caught it after close proximity to infected birds.
It is far more virulent than the deadly 1918 Spanish flu that caused death in one in 20 cases and killed 50 million.
There have been millions of cases of H5N1 avian flu in birds over several years with few human infections. There is "no significant evidence for human to human spread", Prof Hall says. "The recent identification of the virus in Turkey has not been associated with any human infection. It is not a common characteristic of the virus." However there is a risk the virus could adapt after passing through a human host making it much more infective and allow human to human transmission.