Scientists Race for Vaccine Against Killer Flu
By Robert S. Boyd
WASHINGTON – Under a microscope, it’s only a tiny ball covered with knobs and bumps, hardly worthy of its reputation as a mass killer. But within its shell, it harbors biological machinery that can be deadlier than a nuclear war.
This fearsome creature is the virus that causes bird flu. It usually infects chickens, ducks and turkeys, but it also can jump to humans. Under the right conditions, it could spread like wildfire and kill millions of human beings.
Health authorities consider another worldwide flu pandemic, like the three mass infections that killed as estimated 50 million people in the 20th century, to be both inevitable and overdue.
“There is a storm brewing that will test us all,” World Health Organization Director-General Lee Jong-wook warned late last month. “Failure to take this threat seriously and prepare appropriately will have catastrophic consequences.”
President Bush summoned leaders of three vaccine manufacturers to the White House Friday and urged them to step up their efforts to make a vaccine that would be effective against bird flu.
“The world is obviously unprepared or inadequately prepared for the potential of a pandemic,” Secretary of Health and Human Services Mike Leavitt told an international flu conference at the State Department on Friday.
Bird flu is different from – and potentially far more dangerous than – the domestic flu virus that afflicts millions of Americans every year. Even though there are vaccines against domestic flu, it still causes about 36,000 deaths a year.
There’s no approved vaccine, so far, against the new, virulent strain of bird flu, which was discovered in Hong Kong in 1997 and is now coursing throughout Asia. It already has killed at least 60 people, more than half of those it infected.
This strain, known as H5N1, is considered so alarming because most humans have not been exposed to it – or to a vaccine against it – and hence have developed no immunity to it.
Scientists, however, have learned a great deal about how the virus works. Its genes have been decoded and its inner mechanism laid bare. Researchers can observe the sneaky tactics it employs to evade the body’s immune system, invade and destroy living cells.
Like any virus, the bird flu variety consists of a small clump of RNA, a simpler version of the DNA that carries the genetic instructions for all living cells. The RNA is surrounded by a coat of proteins – chains of molecules called amino acids.
The virus isn’t technically alive. It cannot reproduce on its own; it must kidnap the genes of a living cell to make more “daughter” viruses.
The most worrisome flu strain is H5N1. Its first human fatalities were reported in Hong Kong in 1997.
Ominously, several genes in the H5N1 virus resemble the “Spanish flu” bug that killed 50 million people or more at the end of World War I, according to a report in last week’s Nature by Jeffrey Taubenberger of the Armed Forces Institute of Pathology in Rockville, Md.
Usually people get the H5N1 virus from contact with birds, but at least one probable case of a fatal, person-to-person infection occurred in Thailand in 2004. An 11-year-old girl caught the disease from household chickens. Before she died, she apparently passed the virus on to her mother and aunt, Kumnuan Ungchusak of the Thai Ministry of Public Health reported in the New England Journal of Medicine on Jan. 27.
The two women perished a few days later.
The major defense against flu is a vaccine, a modified form of the flu virus delivered by a shot in the arm or a nasal spray. The vaccine prompts the body’s immune system to produce swarms of protective molecules known as antibodies. The antibodies attach themselves to the HA or the NA protein, rendering them harmless.
The domestic flu vaccine being distributed in the United States this fall protects against two combinations of viral genes- H1N1 and H3N2 – which have been circulating worldwide since 1997. This vaccine, however, offers little or no protection against H5N1.
Two years ago, an experimental H5N1 vaccine was developed by Robert Webster, a viral expert at St. Jude Children’s Research Hospital in Memphis, Tenn. Webster’s vaccine is being tested in laboratories, but it won’t be available for public use this flu season.
In the last few weeks, the National Institute for Allergy and Infectious Diseases, in Bethesda, Md., awarded multimillion-dollar contracts to companies in California, Maryland and Pennsylvania to develop and stockpile future bird flu vaccines.
Meanwhile, Kanta Subbarao, a viral expert at the National Institute of Allergy and Infectious Diseases, and her colleagues are working to develop vaccines against the H2, H7 and H9 proteins, as well as the dreaded H5.
In addition to vaccines, doctors have a number of drugs to treat patients exposed to or infected with flu.
One such drug, Tamiflu, interferes with the NA protein. This prevents the release of daughter viruses, so an infected person can’t relay the disease to others. However, Tamiflu is only partially effective against the H5N1 virus.