Even before terrorist attacks killed at least 30 and wounded scores more in the heart of Brussels Tuesday, nearly half of Americans said they worried “a great deal” about possible terrorist attacks in the U.S. heartland, recent Gallup polling found. The percentage of Americans who expressed concern — 48 percent— was higher than in most years since 2004.

The survey was conducted earlier in March, amid growing concerns about the Islamic State group, aka ISIS. The group was responsible for attacks in Paris last November that resulted in 130 deaths. Several Americans allegedly supportive of the group have carried out smaller-scale lone-wolf attacks. The findings were similar to polling results in 2015, but higher than years prior.

The violence in Brussels could elevate concerns among Americans. The coordinated attacks targeted an airport and subway station, injuring more than 230 people in addition to the at least 30 people killed. ISIS claimed responsibility for the violence online.

Adding to the nearly half of Americans who said they feared the possibility of future attacks on U.S. soil, 23 percent said they worried a “fair amount.” Just 29 percent said they were not concerned. Older Americans were more likely than young people to say they feared terrorism. 

Despite the relatively high worry, polling indicated that Americans were more concerned about the availability and affordability of healthcare, the economy and crime and violence. Ranking as a number one concern, 55 percent of those polled said they worried “a great deal” about healthcare. 

Unlike many European nations, the U.S. is largely considered safe from ISIS members trained in Syria and Iraq in paramilitary tactics. Whereas hundreds of European ISIS supporters have returned home, prompting major security concerns, U.S. officials fear self-radicalized, homegrown individuals who might be inspired by the group. There were reportedly 60 terrorism-related cases prosecuted in the U.S. in 2015 — higher than any year since 2001.

Despite heightened security in several big cities, most Americans went on as usual with their days.

“While we take this threat seriously, we will not live in fear,” New York City Mayor Bill de Blasio said. “Our lives will continue today in honor of those lost to terrorism. Securing New York City is our show of solidarity with the people of Brussels and the victims of terrorism worldwide.”