When should we start social distancing? Now.

"Should I cancel my trip?" "Should I skip that meeting, concert or community event?" "Should I visit my grandparents in assisted living?" "Should I ask my employer if I can work from home?"

With more than 100,000 cases of COVID-19 reported globally and states reporting new cases daily, Americans are asking themselves the right questions about how to reduce their risk of infection. But most of us are making these decisions based on the risk we perceive that the virus poses to ourselves and our families. Instead, we must now begin thinking about the large and important role we each play during this pandemic: We are all potential links in chains of infection. These chains have the capacity to encircle our communities, our country and the world. Indeed, many undetected chains of transmission are occurring in communities around the country. The time to act to stop transmission is now.

What makes COVID-19 so terrifying is both the virus's potential to cause a high number of deaths and that it is highly infectious. Even if 1% of cases end in death, that's hundreds of thousands of deaths we need to prevent.

As Dr. Richard Hatchett, CEO of the Coalition for Epidemic Preparedness Innovations, noted in a recent interview, the ability of this virus to cause serious disease or death combined with the extraordinary contagiousness of the disease is most concerning. On Feb. 26, less than two weeks ago, Italy had identified 400 cases, less than half of the total number of cases reported in the U.S. to date. As of March 10, Italy had reported more than 12,000 cases and 800 deaths and had quarantined the entire country. The first-rate health care system is entirely overwhelmed, and doctors are having to ration care.

The speed at which a new disease will continue to spread depends upon a number of factors. One key factor is the contact rate, the rate at which infected individuals come close enough to others to spread the disease. Reducing the contact rate and slowing down the person-to-person spread of the virus is critical to preventing the impact of this outbreak on our families, our communities and the health care system. Each person who avoids infection breaks a link in a potential branching transmission chain. By avoiding the infection, we not only avoid passing it to a vulnerable co-worker or an elderly neighbor, we break a chain that could otherwise result in dozens if not hundreds or thousands of cases over time.

What do we need to do to avoid contracting or spreading this infection? Social distancing is the most important approach and is urgently needed. This encompasses policy-driven approaches such as travel restrictions and telecommuting. During an epidemic or pandemic, local, state and national leaders and public health officials must determine how best to implement policies to protect communities before an outbreak sparks a crisis. Now is the time for such leaders to enact effective and equitable policies that are likely to mitigate the impact of COVID-19. Indeed, now is the time for all of us to integrate social distancing into our daily lives.

We do not need to wait for a policy directive to contribute to slowing the spread of this outbreak. Social distancing also includes actions we all can take to minimize our in-person contact with others. This means canceling or deciding not to attend gatherings and working from home. It means limiting in-person meetings and placing workstations at least several feet apart if it is not possible to work remotely. It means canceling all nonessential travel. We must ask ourselves before leaving home, "Do I need to go out?" Good hygiene practices, including proper hand-washing, covering coughs and sneezes, avoiding surfaces that may be contaminated, and staying at home when sick are very important, as is calling a clinic ahead of time if one has symptoms and is planning to seek care.

The goal of these behavior changes is not just to protect ourselves; it's to slow the spread of infection within the entire population and protect us all. In public health, this is called "flattening the curve," referring to the change in infectious-disease cases over time. An epidemic curve will initially rise as the number of cases increase, peak, and then case reports will drop off. Social distancing helps push the timing of the peak number of cases further into the future so that we have more time to prepare.

If the outbreak spreads too rapidly and cases spike too quickly, the health care system can become stretched beyond its capacity to treat the number of cases that require significant care. When we reach the point where the system is overwhelmed and can no longer handle any health problem, all Americans are in danger, because hospitals, ICUs, clinics and providers will not be able to adequately treat incoming COVID-19 cases or other urgent health needs. Those with COVID-19 plus people who are pregnant, children needing cancer treatment and adults requiring dialysis, will all suffer when the system is overloaded. Once communities reach that point, it will be very difficult to manage the impact of such a crisis. We have no choice but to take steps to flatten the curve now to buy precious time.

In the absence of a widespread COVID-19 vaccination (which won't be available for more than a year, at its earliest), social distancing is something we all need to do to disrupt the virus's ability to spread unabated. It's unclear how the extensive mitigation policies in China and Italy might play out in the U.S., but individual behavioral changes are important even in the absence of policies, which may be implemented too late to be fully effective. Indeed, a recent paper in Science that modeled the impact of travel limitations on disease spread found that preventing spread by adopting behavioral changes like social distancing are more effective than travel restrictions alone.

The rapidly changing landscape of COVID-19 spread in the U.S. means time is of the essence. We still have the power and the responsibility to choose to make behavior changes that can contribute to pandemic control, if this action is adopted on a large scale. Think about what you can do on a day-to-day basis to reduce your contact with others in your community, in your workplace and in public.

As more testing rolls out across the U.S., case reports are certain to rise. If we do nothing, they will continue to rise unabated. If we each make a commitment to adopt as many common-sense social distancing measures as we can as soon as possible, we can all contribute to flattening the curve and slowing the spread of the disease. Do not think that because your individual risk of infection is low, you should do nothing. If you care about your family and your community, take as many steps as possible to reduce your contact with others now.