Bioterrorism remains a major threat for the United States despite more than $65 billion spent on protecting the country from myriad dangers, the Bipartisan WMD Terrorism Research Center said in its latest report Wednesday.

The center's Bio-Response Report Card evaluated U.S. preparedness for countering threats from bioterrorism and found the country remains vulnerable to multiple threats and "largely unprepared for a large-scale bioterrorist attack." More than two dozen of the leading U.S. bio-defense experts took part in the investigation.

The report was awaited by security organizations as an indicator of what more needs to be done in the United States and abroad to deal with bioterrorism, which became a focus of attention as part of overall defense strategies after the Sept. 11, 2011, attacks on the United States.

Bioterrorism alerts have driven other governments including U.S. allies to invest more in equipment and training to deal with potential incidents involving a wide range of threats that are categorized as bioterrorism.

The anti-bioterrorism alerts have already led to more sophisticated scanning devices being introduced at airports and other points of cross-border traffic, at private and public buildings and in areas frequent by large numbers of people.

The center, a not-for-profit research and education organization, estimates that since the October 2001 anthrax attacks, the U.S. government has spent more than $65 billion on biodefense. The center maintains the spending was done "without an end-to-end, strategic assessment of the nation's bio-response capabilities."

The report card's evaluation assigned letter grades measuring U.S. preparedness and progress in "protecting the American people," the center said.

No comparable reports are available from other countries but increased awareness of potential terrorism has led to measures against bioterrorism in other countries, including states that are part of the military coalitions in Afghanistan and before that in Iraq.

Former U.S. Sens. Sen. Bob Graham, D-Fla., and Sen. Jim Talent, R-Mo., the chairman and vice chairman of the WMD Center, led the report's publication as "an objective, strategic analysis" of the U.S. readiness "to respond to various levels of biological disasters."

Advances in biotechnology have enabled a small team of individuals with college-level training to create deadly biological weapons, maintains the report.

"A thinking enemy, armed with biological weapons, could change the very nature of America -- our economy, our government and even our social structure," said Graham. "America does not yet have adequate bio-response capability to meet fundamental expectations during a large-scale biological event."

The report assessed U.S. capabilities in seven categories of bio-response in relation to the magnitude of potential biological scenarios, from "small-scale non-contagious" to "global crisis contagious." The report hands out 45 letter grades ranging from Bs to Fs.

Bs were awarded in categories related to small-scale attacks while Fs were prevalent in the categories under "large-scale" and "global crisis." There was a smattering of Cs, including in regards to communication.

The report said the United States faced three strategic priorities top of which was "leadership that sets clear priorities and engenders commitment and unity of effort. The other priorities were mobilizing "whole of nation" response planning and more investment in purpose-driven science, it added.