“It was striking that this was not regular influenza we were looking at, whatever it was,” Fukuda later told me. Ordinary flu preyed on the weak: infants, the elderly, and the infirm. But this strain had demonstrated that even the young and healthy—especially the young and healthy—were its targets. “What does it look like?” he asked. “It looks like young people dying from something new. So it really brought us back to 1918.”
The parallels were eerie. Ordinary flu has what scholars describe as a U-shaped mortality curve, with deaths concentrated among the very young and very old and a far lower proportion among those in between. The milder pandemics of 1957 and 1968 adhered to the same pattern. But during the Spanish flu of 1918, more than half the deaths were among those between eighteen and forty. This gave the disease a W-shaped mortality curve, reflecting the heavy toll in the middle of life as well as at the beginning and end. The avian flu outbreak in Hong Kong was much the same. And after the virus resurfaced in 2003, spreading its reach across much of East Asia, the deaths continued to follow this disquieting pattern. The largest toll was among those between ages ten and nineteen, followed by those in their twenties. The overall case-fatality rate was highest among those between ages ten and thirty-nine.
“Most of the time in public health and in medicine,” Fukuda continued, “there’s a fair amount of uncertainty, but you rarely come across issues where there’s a really high degree of uncertainty and what you’re sitting on may be something like a 1918. You feel like, ‘I don’t know what is going to happen. I don’t know what is going on. But what is going on is not good, and what it reminds me of is the worst not-good of the century.’”
Researchers have yet to account fully for why the Spanish flu and avian flu, alone among contemporary flu outbreaks, manifest this W-shaped curve. “Explaining the extraordinary excess mortality in persons 20-40 years of age in 1918 is perhaps the most important unsolved mystery of the pandemic,” wrote researchers at the U.S. National Institutes of Health. The answer could lie with another uncanny similarity between the two viruses. Historical accounts from 1918 and experiments on a version of the Spanish flu strain resurrected in the lab reveal that it also provoked tremendous cytokine storms, those withering counterattacks by the body’s immune system. Scientists speculate that the young and healthy may be most vulnerable because, ironically, they have the most robust immune systems, thus the ones that launch the most vicious and ultimately suicidal responses. These victims may be undone by their own strength.
Scientists’ understanding of this novel bird flu strain is still evolving, and the more they learn, the more they worry. Some now suspect that bird flu is moving down the same path as the virus responsible for the deadliest epidemic in human history. “This is a kissing cousin of the 1918 virus,” warns Michael Osterholm, director of the Center for Infectious Disease Research and Policy and a frequent commentator on the pandemic threat.
Spanish flu, like bird flu, is thought by scientists to have been a wholly avian virus that developed solely through a series of internal mutations, as opposed to the genetic reassortment that spawned the 1957 and 1968 strains in addition to the swine flu of 2009. Some of the mutations discovered in the 1918 virus look familiar. “Notably, a number of the same changes have been found in recently circulating, highly pathogenic H5N1 viruses that have caused illness and death in humans and are feared to be the precursors of a new influenza pandemic,” wrote a team of researchers led by Jeffrey Taubenberger, the American scientist who first fully analyzed the genes of the 1918 virus. Just since 1997, bird flu has become more like the Spanish flu strain. A series of studies shows bird flu has grown more virulent and less susceptible to antiviral drugs. “The H5N1 avian flu viruses are in a process of rapid evolution,” said researcher Elena A. Govorkova in 2005. “We were surprised at the tenacity of this new variant.” A later lab study suggested that bird flu may have already become more ferocious than the 1918 virus, laying even greater waste to the respiratory system and, fiendishly, targeting those lung cells specifically involved with repairing damaged tissue. In September 2006, WHO brought the world’s premier flu specialists to Geneva to scrub the evidence. Malik Peiris, the renowned microbiologist from Hong Kong, told the three dozen participants at this private session something that took their breath away. If the virus continued to develop along the same path, ultimately emerging as a pandemic strain through internal mutation rather than genetic reassortment, its high lethality could persist. He concluded there was no scientific reason for expecting a decrease in the fatality rate, currently at 60 percent of recorded cases. His comments, though later reported by WHO, were largely overlooked by the media. Their import was horrifying. Once the virus evolved into a form easily passed among people, it would be expected to infect a quarter of humanity. So even if the actual fatality rate was only 50 percent after accounting for overlooked mild cases, this could mean the deaths of nearly a billion people.
That figure is so big as to be incomprehensible. Researchers would rather dwell on scenarios more akin to 1918. That strain claimed fewer than five percent of those it infected. If the coming pandemic follows suit, the global death toll would only be 62 million, according to one extrapolation.
The World Bank originally projected that a severe pandemic could cost the world economy $800 billion in the initial twelve months. By late 2008, the World Bank had nearly quadrupled this estimate, concluding that an epidemic would cost about $3.13 trillion during the first year. Even a mild pandemic, like the 1968 Hong Kong flu, would cost $450 billion, and a moderate one like the 1957 Asian flu would reach $1.3 trillion.
The gloom was suffocating in those final weeks of 1997, like the cold, foul mist wrapping Hong Kong’s steep slopes and settling on its myriad islands. A small, tongue-shaped islet called Ap Lei Chau had become the latest focus of the city’s collective anxiety.
Five-year-old Chan Man-kei had been playing with friends at her kindergarten, a brightly decorated school on the ground floor of a public housing project in Ap Lei Chau, when she started throwing up. Her parents had been called. A doctor had referred her to nearby Queen Mary Hospital, where her lab samples tested positive for bird flu. About a week later, on Tuesday, December 16, Hong Kong health officials announced that two of her younger cousins had also been hospitalized in Queen Mary’s isolation ward. They, too, might have the virus.
Hours after that disclosure, Fukuda and Chan addressed the press about the heightened prospect of human transmission. “It’s a possibility in this case and one of the things we are concerned about,” Fukuda acknowledged at the evening news conference. Chan agreed that Man-kei might have infected her cousins. “They live together at Grandma’s and play together,” she said. The health department was trying to crack the case, she told reporters, assuring them, “We are working at breakneck pace.”
Ap Lei Chau was connected to the southern shore of Hong Kong island by a bridge. A decade earlier, the government had erected several dozen brown-and-gray high-rise apartment buildings on the green hillsides of Ap Lei Chau, and about ninety thousand people now lived there, making it one of the most densely populated islands on Earth. Man-kei’s two younger cousins and a third sibling stayed with their parents and grandparents in an apartment barely three hundred square feet in size. This was often where Man-kei spent her days.
When health investigators arrived at the apartment, they were rebuffed. The family patriarch, a sixty-four- year-old watchman, refused to speak with them or provide blood samples to see if he’d been exposed to the virus. Other family members were also reluctant to talk. They were afraid of being stigmatized or shunned by neighbors spooked by this new, mysterious plague. Fukuda arranged to meet one relative secretly at a cafe, the first of several clandestine interviews health officers conducted over the course of the outbreak. Eventually, they were able to tease out a history of the children’s recent activities, noting what they had done together and what they’d done separately. (Only one of the younger cousins ultimately tested positive for the virus. All three children survived.) But the source of their infection remained elusive.
Chan was frustrated. She couldn’t visit Ap Lei Chau herself because of the media frenzy this would cause. Nor was she getting a good sense of the family and its surroundings from the investigators. She kept sending them back to scare up more details, instructing them to observe the neighborhood at different times of day and different days of the week.
“I want to know exactly what is going on,” she insisted. “What do the children do?”
“They play in the car park,” came the response. “That’s their play-ground.”
Chan wanted to be able to picture the parking lot. She told them to take photographs and draw her a map. They did. Nothing seemed amiss.
But when the team returned to Ap Lei Chau the following Sunday, they spied cages of geese in the parking lot at the base of the apartment tower. There were several stalls near the entrance. Perhaps they’d been there on previous occasions and the children had passed too close. The investigators snapped some photographs and later presented them to Chan. They were all thinking the same thing.
Samples were taken from the grubby cages and tested. “Bingo,” Tsang recalled. “We found a positive swab in one of the stalls.”
