One thing certain about the flu is uncertainty, according to Marc Lipsitch, a professor of epidemiology at the Harvard School of Public Health and a prominent authority on the spread of infectious disease.

The rise and rapid spread of H1N1 flu virus, known as swine flu, has kept Lipsitch busy in recent months. An expert in computer modeling of disease dynamics, Lipsitch has been part of a team advising federal officials on swine flu’s likely behavior and the government’s response to it.

In April, shortly after the flu hit the headlines, Lipsitch was called to Atlanta as an adviser to the U.S. Centers for Disease Control and Prevention. For a week, he worked intensively with other advisers and officials there to provide analysis and perspective. He appreciated, he said, how difficult the job of health policymakers is in the early stages of a pandemic, when difficult decisions are being made on the basis of still-sketchy information about how dangerous and contagious a pathogen is.

“Academics have the ability to spend more time thinking about these questions than people who provide valuable services,” Lipsitch said. “I felt frantic the whole time, but not nearly as frantic as the people who had to [make decisions] each day.”

Lipsitch kept in touch with officials in Atlanta after he returned to Boston through conference calls, at first daily and now weekly.

Last summer, as a member of the 2009 H1N1 Working Group of the President’s Council of Advisors on Science and Technology, he helped draft an assessment of the federal government’s handling of the swine flu outbreak so far. He gave it high marks, particularly for its flexibility.

Flexibility is key in handling an outbreak’s beginning, he said. Because officials didn’t know how dangerous H1N1 was, the initial response included fairly dramatic steps, such as closing schools if a case were diagnosed there. Those responses were dialed back as officials began to understand that, while contagious, H1N1 wasn’t as deadly as past pandemic flus have been — at least so far.

“People took it seriously and then scaled back as the nature of it was shown,” Lipsitch said. “The response was well-tailored to cover the range of possibilities at any one time.”

Lipsitch was recently named the head of a new center at the Harvard School of Public Health designed to provide better information about disease outbreaks to public health officials and policymakers. The Center for Communicable Disease Dynamics, which received a $10 million grant from the National Institutes of Health, will focus on mathematical modeling of seasonal infectious diseases such as the flu, on drug resistance, and on the best ways to allocate resources in interventions.

Lipsitch said that more people with such public health expertise are needed in the United States, so part of the center’s mission will also be to educate a new generation of students in the discipline.

Lipsitch, who received his doctorate from Oxford University in 1995, has considerable experience to lend to the effort. Much of his study has focused on the pathogen that causes pneumonia, childhood ear infections, and meningitis, Streptococcus pneumoniae. He has evaluated how it spreads, how it is affected by interventions, and what the patterns of drug resistance are. He also worked on the 2003 outbreak of severe acute respiratory syndrome, or SARS, and has worked to better understand the 1918 Spanish flu that killed millions around the world.

With the Northern Hemisphere flu season looming with the pending of winter, Lipsitch said uncertainty remains about the nature of the flu’s coming second round. Though H1N1 is so far not as severe as past flu epidemics, it is clear that some will die from the ailment, Lipsitch said. Vaccines, which are being rushed through development and distribution, will be available in October, but it takes time to administer the dose and more time for the body to develop immunity.

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