Flu (Influenza)
A seasonal respiratory virus. Flu circulates year-round in tropical regions and during opposite seasons in the southern hemisphere, so a recent shot is advised for most international travellers.
What it is
Influenza, or flu, is a respiratory virus that causes fever, body aches, sore throat, and cough. It can be serious for older adults, young children, pregnant people, and anyone with chronic conditions.
How it spreads
Through coughs, sneezes, and droplets in close contact. It also spreads from contaminated surfaces.
Dosing & timing
- Primary series
- One dose each flu season.
- Boosters
- Get a fresh dose each year — the strains in the vaccine are updated annually.
- Before you travel
- Ideally at least 2 weeks before travel to areas with active flu circulation.
Who should consider it
CDC recommends an annual flu shot for nearly everyone aged 6 months and older. For travellers, it matters because flu circulates year-round in tropical regions and during opposite seasons in the southern hemisphere — so even a summer trip can mean exposure.
Side effects and safety
Common (most resolve in a day or two)
- Soreness where the shot was given
- Mild fever
- Muscle aches
- Feeling tired
Serious but rare
- Severe allergic reaction (very rare)
Who should not get it
Skip it if you have had a severe allergic reaction to a previous flu vaccine. Tell your provider about any egg allergy — most flu vaccines are safe even for those with egg allergy, but your doctor may pick a specific brand.
Common questions
I had my flu shot at home — do I need another for the southern hemisphere?
Usually no. A current-season shot covers travel to either hemisphere.
Can the flu shot give me the flu?
No. The injected vaccine does not contain live virus. You may feel mildly off for a day, but that is your immune system responding, not flu.
When is flu season in the tropics?
There is no strict season — flu circulates year-round in tropical regions, so a current-season shot is a good idea any time of year.
Plan ahead: Talk to a travel health doctor 4 to 6 weeks before departure to time your flu shot with your trip.
Source: CDC — Flu (Influenza).
Disclaimer:This information is for general guidance only, based on CDC Travelers' Health. It does not replace advice from a qualified travel health professional. Consult a doctor 4–6 weeks before your trip.