The COVID-19 pandemic, which was first reported in the U.S. in March, is spreading across multiple states, especially in the South and West. Researchers and scientists are scrambling to understand the hows and whys of the virus in hopes of finding a solution to slowing or stopping the spread of the deadly virus. But recent reports paint a grim picture: We have a minimal idea who among us are spreading the virus.

Health officials report new confirmed coronavirus cases daily. These patients have developed telltale signs - cough, difficulties in breathing, and fever. However, the toll of confirmed cases does not include an elusive bunch of spreaders: the asymptomatic patients.

According to an estimate released by the U.S. Centers for Disease Control and Prevention, about 40 percent of coronavirus infections across the nation is caused by infected individuals who display little to no signs often associated with the virus.

Why are asymptomatic cases happening?

COVID-19 is a very evasive virus, making it harder for researchers to understand the biology of the disease fully.

In recent months, federal health agencies and organizations such as The World Health Organization said that people with underlying health conditions are more likely to develop severe coronavirus symptoms. But scientists have yet to discover why some do not get symptoms at all.

The biggest challenge in studying how asymptomatic cases transmit the virus is by finding out how often it happens. The recent surge of COVID-19 cases in the U.S. led officials to cut back on widespread testing. The setback directly affects data that would show the actual figures of asymptomatic and pre-symptomatic spread.

Research studies also show that health officials may be failing in following up on patients after testing to see if they might have developed symptoms. A study published in Nature estimated that Chinese health officials might have missed over 87 percent of infection in Wuhan during the early months of the pandemic.

How contagious are asymptomatic and pre-symptomatic individuals?

It is unclear how contagious asymptomatic individuals are. Part of the reason is that researchers face difficulties in documenting the transmission of the virus involving individuals who show no symptoms.

The C.D.C. estimates that asymptomatic cases might be 75 percent as infectious as symptomatic patients. However, the assumption is based on a vague understanding of "viral shedding" in which people unknowingly release contagious diseases into the air.

Chinese research showed asymptomatic individuals do not carry as much of the virus as patients who develop symptoms. A study showed infected people who did not display telltale signs of the infection had a weaker immune response and produced fewer antibodies.

Stanley Perlman, a professor of microbiology and immunology, said the immune system of asymptomatic carriers matches those found in bats. The immune response in the flying mammals allowed them to clear the virus, which experts say may also be the case with asymptomatic spreaders.

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