Even among microbiologists and virologists, characterizing an influenza pandemic is a bit like, well, defining pornography.
“The old saying is: ‘What’s the definition of a pandemic strain?’ ‘Well, you can’t really be sure but you’ll know when you see one,”’ says Dr. Walt Dowdle, a long-time head of the influenza laboratories at the U.S. Centers for Disease Control, now retired from that post.
That may have seemed a truism at one point. But with the current outbreak of swine flu, it may not seem so anymore.
Though the global count of confirmed cases has crested 10,000 in more than 40 countries on five continents, some politicians say they don’t see a pandemic in the offing.
Some argued at the World Health Assembly in Geneva over whether the World Health Organization should rewrite the definition of a pandemic in ways that would exclude this virus. A number — among them several affluent countries with antiviral stockpiles and pandemic vaccine contracts — insisted the lack of severity associated with this new strain of flu means it doesn’t merit the name.
The job of defining what constitutes a pandemic belongs to scientists, not politicians. But even scientists have divergent views about what is unfolding with the new H1N1 virus.
“I think it is a pandemic already,” says Dr. Allison McGeer, an influenza expert at Toronto’s Mount Sinai Hospital, which this week admitted two H1N1 patients. On Wednesday, Ontario’s confirmed case count jumped 45 per cent, to 272 from 187.
But Dr. Peter Palese, head of microbiology at Manhattan’s Mt. Sinai School of Medicine, offers a differing opinion.
“In the past we talked about a 1918 pandemic, a 1957 and a 1968. And if you use it in that sense, in the classical sense of serious pandemic, then obviously (with) the swine H1N1, the name is not justified.”
After years of fearing the next pandemic would be triggered by the dangerous H5N1 avian flu virus with its 60 per cent case fatality rate, flu scientists were as taken aback as everyone else by the out-of-left-field emergence of this swine flu virus.
It’s an H1N1 virus, meaning it bears hemagglutinin (H) and neuraminidase (N) proteins on its surface that are distant relatives of those found on a human flu strain — also called H1N1 — that has been circulating for most of the last century.
It used to be thought that to cause a pandemic, a virus with a new hemagglutinin had to break out of nature.
This virus’s hemagglutinin is not brand new — but it is new enough to a wide segment of society to be able to infect a lot of people, especially young people, quite easily. But there are hints that exposure to H1N1s that circulated before 1957 may have given people in their 60s and older some protection against this new virus.
That fact, combined with the mildness of most cases and the low number of deaths, has some scientists wondering if this really is a pandemic strain in the making.
However, the WHO’s criteria for a pandemic deliberately don’t take severity into account, focusing instead on spread of a new virus to which a large portion of the population has no immunity. Severity, the WHO says, will likely vary from place to place, depending on the vulnerabilities of different populations. As well, it could change over time as a new virus spreads in waves around the world.
By the WHO’s definition, a virus crosses the pandemic threshold when there is evidence of spread in the community in two WHO regions. With the virus galloping through schools in Japan, many observers believe the call is imminent — if the WHO does not bow to pressure to change the rules.
Infectious diseases expert Dr. Michael Osterholm says the agency will hurt its own credibility if it bends scientific reality to political will.
“You know, you can decide not to call a house burning down a fire because it can only be a fire if it’s so many acres big. But it’s still a fire,” says Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy.
“I’m worried that if we get into this pandemic, not pandemic debate, we’re only going to see WHO suffer miserably in terms of their scientific integrity. That’s what I think would be really unfortunate. Because we need to have a strong international public health agency whose credibility rests on its scientific word.”
To Osterholm’s eyes, the situation is clear: The novel H1N1 virus is causing a pandemic.
One of the grand old men of flu agrees this virus will earn pandemic moniker, though he says swine flu will probably go down in the annals of pandemics as a minor event.
“My prediction would be that it’s going to be further transmitted and will become pandemic in the sense of global in distribution,” says Dr. Edwin D. Kilbourne, who played key roles in the responses to the 1968 pandemic and the 1976 swine flu incident.
“But it’s not going to be a very important disease in terms of mortality,” predicts Kilbourne, who lives in Madison, Conn. “And perhaps not even in terms of total morbidity.”