>>14233465Lots of possible reasons. There's no information on what this population is from. Maybe it's from somewhere in the third world and during the middle of the year, the insect population increases, spreading disease to newborns. If you're born in the cooler months, the insects are gone (and dying off for the year). By the time they come back, your body has developed a strong enough immune system to have a chance against insect borne diseases.
Or maybe it's somewhere with terrible air pollution, which subsides during the cooler months. There are lots of seasonal effects that vary greatly across the world.
pic unrelated
