A mild first wave of flu pandemic could reduce deaths from a future outbreak of more severe infection, a new analysis suggests.

A review of the effects of the 1918 flu pandemic on American soldiers and British sailors and civilians found that people who were infected during the first, milder spring and summer wave had a 35 percent to 94 percent lower risk of catching the more severe strain than those who weren't infected earlier. The higher end of that continuum is similar to the 70 percent to 90 percent protection offered by vaccines.

Their risk of death also was 56 percent to 89 percent lower, according to an analysis published in the Journal of Infectious Diseases. Scientists from the National Institutes of Health, George Washington University and Tulane and Xavier Universities in Louisiana conducted the analysis.

"You wouldn’t want to eradicate this wave because it probably provided protection," says study author Lone Sinonsen, a visiting professor of global health at George Washington University School of Public Health and Health Services.

Still, it may be difficult to apply that conclusion in another pandemic, she says.

"You have to judge how severe [a disease outbreak] is before deciding whether to close schools and movie theaters and suffer the consequences of all that," Simonsen says. "It's going to be very hard to judge that in real time."

Richard Hatchett, associate director of emergency preparedness at the National Institute of Allergy and Infectious Diseases (NIAID), agreed.

"I'm not sure there is any direct application of the results of this paper to current pandemic planning," Hatchett told the University of Minnesota's CIDRAP News.

The Department of Health and Human Services calls for isolation of patients and voluntary quarantining of family members, as well as closing schools, depending on how severe a flu outbreak is. "I think their [the study authors'] recommendation of not implementing aggressive nonpharmaceutical interventions in a mild pandemic is in line with what the government is currently recommending," Hatchett told CIDRAP.

(CDC microbiologist Terrence Tumpey examines a reconstructed 1918 pandemic influenza virus/Public Health Image Library)