The next flu pandemic could appear in spring or summer rather than winter, according to researchers.

They found that while winter is the normal flu season, many major flu outbreaks were first detected between late March and early July. That includes the 1889, 1918 (the Spanish flu), 1957, 1968 and 2009 (the swine flu) epidemics, The New York Times reported.

A person with the seasonal flu may have some protection against other flu viruses, even genetically different ones, according to Spencer Fox, a graduate student in infectious disease modeling at the University of Texas at Austin and one of the study authors.

That protection lasts about six weeks and even a highly infectious flu virus would be temporarily slowed during the winter if a large proportion of the population already had the seasonal flu, Fox told The Times.

But the new virus could take hold once that protection fades. That would be in late March at the earliest.

The study was published in the journal PLoS Computational Biology.