The Centers for Disease Control and Prevention on Monday updated guidance to say that Americans who have recently been exposed to someone with COVID-19 for more than 15 minutes and do not have symptoms do not need to get tested. "You do not necessarily need a test unless you are a vulnerable individual or your health care provider or state or local public health officials recommend you take one," the CDC said. This is a change from previous guidance that said people who had spent more than 15 minutes with an individual who has tested positive for the virus should also get tested, regardless of symptoms. The U.S. has conducted more than 73 million tests this year, and about 6 million of them have come back positive. The CDC's decision has been criticized by some in the medical community. "Our work on the 'silent' spread underscores the importance of testing people who have been exposed to COVID-19 regardless of symptoms," Alison Galvani, an epidemiologist and director of the Center for Infectious Disease Modeling and Analysis, tweeted . "This change in policy will kill." It is estimated that up to 40% of people who have COVID-19 are asymptomatic, meaning they do not demonstrate common symptoms of an infection like coughing or muscle aches, according to one research letter published in May in JAMA Network.