Several conspiracy theories were offered up around the Zika virus in 2016 as the disease spread across South America, then the rest of the world. One of the most outlandish of these rumors, the claim that Americans are immune to the virus, was posited on Twitter in May 2016:

No scientific body, whether it is from the United States or anywhere else in the world, has reached the conclusion that Americans are immune to the Zika virus (nor is there any scientific reason U.S. citizens could be immune). In fact, the Center for Disease Control has issued a warning to any American traveling to destinations such as Mexico, Central America, or the Pacific Islands:

Local mosquito transmission of Zika virus infection (Zika) has been reported in Costa Rica. Local mosquito transmission means that mosquitoes in the area are infected with Zika virus and are spreading it to people. Because Zika virus is primarily spread by mosquitoes, CDC recommends that travelers to Costa Rica protect themselves from mosquito bites. The mosquitoes that spread Zika usually do not live at elevations above 6,500 feet (2,000 meters) because of environmental conditions. Travelers whose itineraries are limited to areas above this elevation are at minimal risk of getting Zika from a mosquito. The following map shows areas of Costa Rica above and below 6,500 feet.* For more information, see Questions and Answers: Zika risk at high elevations. Sexual transmission of Zika virus from a male partner is also possible, so travelers are also encouraged to use condoms or not have sex.

Hundreds of people in the United States have already been infected by the disease. According to the Centers for Disease Control and Prevention, more than 500 Americans have already contracted the disease, and researchers at the annual meeting of the Global Virus Network warned that disease will likely become a permanent part of American life, as with West Nile Virus:

Once Zika virus arrives in the United States, it will be here to stay. Leading experts now predict that the mosquito-borne disease will become a constant low-level threat that Americans will need to be vaccinated against routinely—as we do now for rubella, a virus that, like Zika, causes birth defects. That is, once there is a vaccine for Zika. The earliest possible deployment of Zika vaccines could be several years away…

On 24 May 2016, researchers from Johns Hopkins University, George Washington University, and the University of Georgia published a study in the scientific journal Vaccine that examined Zika-related conspiracy theories. While claims that Americans are “immune” to the virus were not specifically addressed, the researchers did warn that misinformation on the internet could prove to be a significant health hazard:

In the new study, the research team members unearthed several unfounded Zika-related claims. Some conspiracy theorists claimed that the increase in microcephaly was caused by the measles, mumps, and rubella (MMR) vaccine. They also insisted that drug companies were blaming Zika virus in order to earn profits from the sale of future Zika vaccines. When other people who are searching for information about Zika come across a story like this, it may lead them to avoid vaccination and distrust health authorities, the researchers concluded. “Once people have made up their minds about something, it’s hard for them to change their opinions,” said lead author Mark Dredze of Johns Hopkins. “I’d find it surprising if this sort of story really had no impact whatsoever, and I can’t imagine it would make people more likely to pursue a healthy response.”

Researchers recommended taking swift action to debunk unscientific conspiracy theories around Zika and other viruses in order to make sure that future vaccine campaigns — once the vaccine is developed — are effective.