History shows epidemics are unpredictable

By Bina Venkataraman, Globe Correspondent

When it comes to epidemics, history can teach -- or mislead.

In the winter of 1976, when more than 200 soldiers came down with a bad flu at Fort Dix, NJ, and one died, people around the country panicked. The Ford administration quickly responded to fears of a pandemic influenza -- mindful of the flu that had swept the world and killed millions in 1918 -- by vaccinating more than 40 million Americans, nearly a quarter of the population.

But the pandemic never happened. And the vaccine probably caused more than 500 people to suffer a neurological disorder that can result in paralysis, and it cost the federal government millions of dollars in damages.

Past disease outbreaks can be instructive for public health officials responding to the strain of swine flu that has led to at least 140 deaths in Mexico City and more than 40 confirmed cases in the United States. But the nature of epidemics is that they are unpredictable, say several leading public health figures, and drawing too many comparisons to past experience poses its own dangers.

“Each outbreak has to be evaluated on its own terms,” said Dr. Harvey Fineberg, president of the Institute of Medicine, in a phone interview today. Unlike the 1976 swine flu cluster that never spread beyond Fort Dix, the current swine flu outbreak can spread quickly from person to person, he said, and it has already appeared in disparate locations. But, Fineberg added, the aftermath of the 1976 vaccination campaign holds a cautionary tale. “The big lesson is to prepare by developing the vaccine, but not to combine that decision with the decision to go ahead and use the vaccine.”

In a conference call with reporters today, Dr. Richard Besser, acting director of the US Centers for Disease Control and Prevention, said researchers had begun developing a vaccine against the swine flu but had no plans yet to distribute it.

Some infectious disease specialists suspect the agency is being cautious because of what happened in 1976. “They are sheepish about it,” said Dr. Marc Siegel, a professor at the New York University School of Medicine who has written books about pandemics. “It was almost assumed that it was going to be a massive pandemic without really noticing what rate of transmission, if any, there was.”

Dr. Richard Wenzel, immediate past president of the International Society for Infectious Diseases, said that the death rate associated with this strain of swine flu could mean it has a far worse -- or far less dangerous -- impact than historical examples allow us to predict. He said the key to understanding the scope of the current outbreak will be knowing how efficiently the virus is transmitted and what mortality rate is associated with it -- characteristics that are not yet clear for this virus. “1918 was one of the worst epidemics we’ve had,” he said, because the mortality rate of the flu strain was high.

By analyzing the 1918 flu pandemic, scientists have identified strategies that seemed to control the spread of the virus early on in communities, said Marc Lipsitch, a professor of epidemiology at the Harvard School of Public Health. One example is shutting down schools where cases start to appear. “People start to transmit the virus before they are sick,” Lipsitch said, which means we should not just treat and isolate people who are sick. “When many cases start to appear in a community, it might be appropriate to close all the schools in that community.”

History also offers lessons about how to deal with the social backlash associated with epidemics, said Naomi Rogers, a professor of the history of medicine at Yale School of Medicine. She said the 2003 SARS outbreak, which originated in China, triggered “an unbelievable hysteria around things Asian and things Chinese” that she she fears will now be echoed in this country with respect to people who appear Mexican. She said public officials are aware of the history and seem to be acting cautiously.

“I think there’s a greater concerted political effort now to try to ameliorate irrational and discriminatory fear,” Rogers said.

While it's clear that officials are drawing on history to analyze and respond to the swine flu outbreak, it is unclear how much the public is influenced by the memory or knowledge of past epidemics.

Even though the swine flu vaccine administered 33 years ago proved unnecessary at best and possibly even deadly, the use of the word ‘pandemic' is likely to trigger more demand for vaccines than the regular flu season, said Dr. Louise M. Dembry, director of hospital epidemiology at Yale-New Haven Hospital. “Thirty-five to forty thousand people die per year in the US from the regular flu,” she said. “It’s not that it’s a benign disease even in regular times."