Before you visit South Africa, Australia or South America this summer, you should heed the advice of health officials. According to the Centers for Disease Control and Prevention, northerners traveling to the southern hemisphere or to tropical areas should get flu shots to avoid influenza, which is active year-round in the southern half of the world.

When northerners exit their flu season—October to March—southerners enter theirs (April to September).

What’s interesting this season, though, is that the strains used in the influenza vaccines for northerners who travel south are identical to those used in southern hemisphere vaccines.

Additionally, health experts advise travelers to get vaccinated if they are traveling with someone who has been in these areas, even if they haven’t.

Learn more about flu vaccines here.