A Zika attack rate of just 1 percent across the six states most at risk for the mosquito-borne disease could result in $1.2 billion in medical costs and lost productivity, a new study finds. That’s more than the $1.1 billion in emergency Zika funding that Congress approved last year after months of delay and which is expected to run out this summer.

“One of the troubling things last year was that (Zika funding) was viewed as a cost — every week, there was another delay and more people becoming infected and more chances of birth defects,” study co-author Bruce Y. Lee, an associate professor at Johns Hopkins University Bloomberg School of Public Health, told me. “The problem is that public health is viewed separately from the economy, even though keeping the population healthy is an investment that benefits the economy.”

As soon as Zika virus emerged in Brazil in 2015, Lee and colleagues knew it was only a matter of time before the mosquito-borne virus made it to U.S. shores. So, they began building a computational model to estimate the economic burden that Zika could have on the U.S., with the hope that policymakers use the estimates when deciding how to prepare for and respond to the continuing disease threat. The forecasts of that computational model were published in late April in PLOS Neglected Tropical Diseases, reporting a potential economic burden of billions of dollars.

To generate economic forecasts, researchers considered a variety of Zika scenarios across six particularly vulnerable states: Alabama, Georgia, Florida, Louisiana, Mississippi and Texas. Scenarios varied by the number of people infected (the “attack rate”) and took into account the probability of a pregnant woman becoming infected as well as the likelihood of infections leading to birth defects or Guillian-Barré syndrome. They also considered a number of potential costs, including testing pregnant women for Zika, treating and caring for children born with birth defects, as well as productivity losses. The scenarios took place over a Zika epidemic that spanned 230 days, which mirrored the outbreak duration that occurred in Brazil. Here’s what they found: Across the six states, an attack rate of 0.01 percent would cost society $183.4 million in direct medical costs and lost productivity. At attack rate of 0.025 percent would cost $198.6 million; a rate of .1 percent would cost $274.6 million; 1 percent would cost $1.2 billion; and 2 percent would top $2 billion.

While U.S. Zika infection rates aren’t expected to reach levels seen in South America and the Caribbean, the researchers did offer this perspective: The attack rate of Zika in French Polynesia and that of chikungunya in Puerto Rico — a virus similar to Zika and spread by the same species of mosquito — is higher than 10 percent.

The study also estimated that an attack rate of .05 percent would lead to 10 children born with microcephaly, a rate of .10 percent would lead to 20 cases, and a rate of .75 percent to 150 cases. An attack rate of 0.01 percent would lead to 770 outpatient visits for Zika-infected nonpregnant patients, more than 350,000 ultrasounds for pregnant women and at least one amniocentesis. Each 1 percent increase in the attack rate would result in about 3,500 additional medical screening visits. On medical costs, an attack rate of .05 percent across six states would mean $123.2 million in direct medical costs; a rate of .10 percent in $130.8 million; and a rate of .75 percent in $220.9 million. Part of the Zika-related health care costs would be paid through Medicaid as well. For instance, an attack rate of .05 percent in Louisiana would result in $2.6 million in Medicaid costs.

In calculating productivity losses, Lee and colleagues considered time for additional screenings for pregnant women as well as lifetime productivity losses associated with birth defects and Guillian-Barré syndrome. Total productivity losses across the six states were more than $100 million for an attack rate of .05 percent and more than $700 million for a rate of .75 percent.

Study co-authors Lee, Jorge Alfaro-Murillo, Alyssa Parpia, Lindsey Asti, Patrick Wedlock, Peter Hotez and Alison Galvani write:

Without details regarding the Zika-prevention measures that would be implemented and how effective these may be, it is unclear what percentage of these costs may be averted. Possible targets of Zika control investment could be improved vector control, more extensive Zika screening, and accelerated vaccine development. Assuming a third of the costs could be averted, an attack rate of 1% would justify investments in the $1 billion range.

Lee, who also serves as an associate professor in the Johns Hopkins Carey Business School, said a Zika outbreak could be particularly straining for the six vulnerable states studied, which include some of the poorest states in the nation with more limited resources available to respond to the disease.

As the U.S. heads into mosquito season, state and local public health departments — the agencies on the frontlines of Zika prevention and response — face serious funding problems. At the federal level, an Affordable Care Act repeal, combined with severe budget cuts proposed in the White House budget plan, could significantly slash the budget at the Centers for Disease Control and Prevention. And many local health departments expect continued cuts to public health preparedness funds. According to news reports, CDC officials have cautioned public health departments to not expect new Zika funding after remaining funds run dry.

Lee described the current funding situation as “incredibly short-sighted.”

“(Zika) continues to spread silently, through mosquito populations and through people,” Lee said. “We really have no idea how many people are infected at this point.”

According to CDC, as of May 9, more than 1,800 women in the U.S. have laboratory evidence of Zika virus. For a copy of the economic burden study, visit PLOS Neglected Tropical Diseases.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for 15 years. Follow me on Twitter — @kkrisberg.