Argentina's Western Equine Encephalitis Virus Outbreak Impacts 21 People

Last year, the World Health Organization (WHO) confirmed the first known case of Western Equine Encephalitis (WEE) in more than two decades in Argentina.

Since then, and until January 9, 2024, 21 human cases in Argentina have been confirmed by the WHO/PAHO.

To alert international travelers to this WEE health risk, the U.S. CDC issued a Level 1 - Practice Usual Precautions, Travel Health Notice on January 12, 2024.

WEE is a rare, mosquito-borne viral disease that affects equines and humans. Most human cases are associated with epidemics in birds or horses.

The CDC says travelers to these regions of Argentina should avoid mosquito bites, which can transmit the Eastern Equine Encephalitis Virus (EEEV).

EEEV transmission is most common in and around freshwater hardwood swamps in the Atlantic and Gulf Coast states and the Great Lakes region in the U.S.

Only about 4-5% of human EEEV infections result in EEE.

In the United States, an average of 11 human cases of EEE are reported annually, according to the CDC. There were 7 EEEV neuroinvasive disease cases in 2023, reported by four states.

From 2012-2021, most cases of EEE have been reported from Massachusetts, Michigan, Florida, Georgia, and North Carolina.

As of 2024, the CDC says no vaccine prevents EEE virus infection.

However, the U.S. Army Medical Research Institute of Infectious Diseases developed a human vaccine for EEE in the mid-1980s, but it has never been approved for public use.

The U.S. government recently invested in a vaccine against western, eastern, and Venezuelan equine encephalitis viruses. 

MVA-BN® WEV has completed Phase 1 clinical development demonstrating potential for broad, and long-term protection, with a Phase 2 study planned for 2024.