A new study has suggested that when flu season dies out in the US each spring, some strains of influenza actually migrate, spending the summer in South America and perhaps travelling even farther away.
"The prevailing view that has developed over the past three years or so is the out-of-tropics hypothesis, in which the strains that bring about each temperate flu season originate from China and Southeast Asia, where influenza A is less seasonal," said University of Michigan postdoctoral fellow Trevor Bedford.
Bedford and colleagues analyzed genetic sequences of a strain of influenza that hit patients between 1998 and 2009.
The researchers discovered some strains of flu seem to move on to more hospitable places instead of dying off when flu season ends.
The findings could help researchers design vaccines to target influenza in specific areas, Bedford said.
"We found, for instance, that South America gets almost all of its flu from North America. This would suggest that rather than giving South America the same vaccine that the rest of the world gets, you could construct a vaccine preferentially from the strains that were circulating in North America the previous season. As we gather more data from other regions, this could be done for the entire world," he said.
Also, he said: "By doing this kind of research, we get a clearer idea of where in the world flu is actually coming from. We know that it's mostly Southeast Asia, but now we see that it can come out of temperate regions as well, so our surveillance needs to become more global."
The paper was scheduled to be published online May 27 in the open-access journal PLoS Pathogens.