Mosquito season has barely begun in the U.S., and repellant producers are already selling more than ever. According to the Wall Street Journal, various bug spray products saw sales increase by 100% to 200% in February and Spectrum Brands Holdings (SPB), maker of Cutter and Repel, has been shipping to retailers three times more than it normally would at this time of year.

There is no vaccine or treatment for Zika, so prevention is the only course of action. Though it has mild symptoms in most victims, it has been connected to severe birth defects in infants whose mothers contracted the virus, which is transmitted either by certain types of mosquitoes or sexually. Most cases occur in Central and South America, the Caribbean, and parts of Asia. There have been 193 incidences reported in the U.S. as of March 9, most of which involved people traveling overseas, and 173 in Puerto Rico, the U.S. Virgin Islands, and American Samoa.

“We’ve seen what has happened in Latin America,” a spokesperson for Off maker S.C. Johnson & Son told the Journal. “We are preparing for the eventuality that it will be here.” Many repellant-producing factories have added extra shifts during weekdays and are now operating on weekends.

U.S. companies are cooperating with international government agencies to make shipping repellant over borders easier in the case that demand increases in areas where the necessary chemicals are in low supply. Since the products are considered pesticides, most countries require regulatory approval before they can be imported.