The Southern Hemisphere’s flu season is winding down, and new data shows this year’s flu shot was 34.5% effective in keeping folks there who got influenza from needing hospital care.

Most (68.3%) of those sent to hospital had the A(H3N2) strain of flu, according to the report from the U.S. Centers for Disease Control and Prevention.

The risk reduction seen with the current shot is within historical averages for vaccine potency against H3N2, which typically ranges between 24% and 43%, the report authors said.

The reduction in risk of hospitalization was even greater for people with chronic illnesses, who are always at higher risk for severe flu.

Among this group, getting the flu vaccine cut their odds for hospitalization by nearly 59% compared to those who didn’t get immunized, the researchers said.

All of this “support[s] CDC and WHO’s recommendation that all eligible persons aged [at or above the age of] six months should receive influenza vaccination,” wrote a team led by Erica Zeno, of the CDC’s National Center for Immunization and Respiratory Diseases.

As happens in the Northern Hemisphere, however, rates of uptake of the seasonal flu shot were low in the Southern Hemisphere, with just 21.3% taking advantage of the shot, the report found.

The Southern Hemisphere’s winter flu season typically runs from April through September.

Flu that’s so severe as to require hospitalization can sometimes lead to death. The report authors noted that throughout the Americas, flu claims the lives of up to 71,700 people each year.

The risk rises with age: Zeno and colleagues found that over 59% of those hospitalized were older adults. However, the flu shot reduced the odds of hospitalization among older adults by nearly a third (31.2%), according to the new data.

The findings were published Oct. 3 in the CDC journal Morbidity and Mortality Weekly Report.

The take-home message from the report: Get your flu shot.

“Vaccination remains one of the most effective measures to prevent influenza-associated complications, including death,” Zeno’s team said.

More information: Erica E. Zeno et al, Interim Effectiveness Estimates of 2024 Southern Hemisphere Influenza Vaccines in Preventing Influenza-Associated Hospitalization — REVELAC-i Network, Five South American Countries, March–July 2024, MMWR. Morbidity and Mortality Weekly Report (2024). DOI: 10.15585/mmwr.mm7339a1

Find out more about protecting yourself from flu at the World Health Organization.

Journal information:Morbidity and Mortality Weekly Report