Flu Season Returns to Southern Hemisphere — Vax Before Travel

Southern hemisphere influenza activity has increased but remained below the seasonal thresholds

Australia beach sunset

Over the last decade, an increasing number of countries located in the tropics have considered expanding seasonal influenza vaccinations.

This debate is due to the complexities of seasonal influenza, two challenging questions confront these countries, which are when to vaccinate and which formulation, northern or southern hemisphere to use. 

Each year, decisions are made by various health leaders to produce influenza vaccines for the following season.

From an antigenic evolution perspective, there is no evidence to suggest the need for a 3rd recommendation for vaccine composition specifically for the tropics, says the World Health Organization (WHO).

And, since the 2017-2018 flu vaccination effectiveness (VE) was reported to be just 36 percent, everyone is hoping for better results for the 2018-2019 flu season.

As of early May 2018, in the southern hemisphere, influenza activity has increased but remained below the seasonal thresholds, reports the WHO.

In Chile and Paraguay, SARI levels continued to be reported above the alert threshold. In Brazil, influenza detections of predominantly influenza A viruses increased slightly.

The WHO’s laboratories have tested more than 97,697 specimens, which 9,993 (10.1%) were positive for influenza viruses.

Worldwide, seasonal influenza subtypes A and B accounted for approximately the same proportion of influenza detections as last year. Among positive viruses, 56.1% were typed as influenza A 43.9% as influenza B.


Of the sub-typed influenza A viruses, 54.6% were influenza A (H1N1)pdm09 and 45.4% were influenza A (H3N2).

Of the characterized B viruses, 84.9% belonged to the B-Yamagata lineage and 15.1% to the B-Victoria lineage. 

In late February, the WHO made its recommendations as to which influenza strains to include in vaccines used in the 2018-2019 northern hemisphere influenza season:

  • an A/Michigan/45/2015 (H1N1)pdm09-like virus;
  • an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus;
  • a B/Colorado/06/2017-like virus (B/Victoria/2/87 lineage); and
  • a B/Phuket/3073/2013-like virus (B/Yamagata/16/88 lineage).

For people traveling to the Southern Hemisphere, if you need a flu shot, vaccines are available at most pharmacies offering several FDA approved flu vaccines.

Travel vaccination appointments can be requested here. 

The CDC Vaccine Price List provides the private sector prices for general information.

Flu vaccine discounts can be found here.

Vaccines, like any medicine, can have side effects, says the CDC. You are encouraged to report negative side effects of vaccines to the FDA or CDC.