How Not to Get COVID-19: What We Know and What We Don’t

Research tells us how the virus spreads and how to stay safe.

Posted May 15, 2020

Fabian/Adobe Stock
Source: Fabian/Adobe Stock

As states across America begin to reopen after months of closures due to the coronavirus pandemic, people must make individual decisions about how much exposure they have to other people. Meanwhile, scientists across the globe are racing to learn as much as they can about how COVID-19 spreads and the best ways to keep people from contracting the disease.

Although the evidence is currently limited, epidemiologists and public health experts have learned some lessons about how the virus spreads and steps you can take to stay safe. Here’s what we know to date:

One of the most dangerous aspects of COVID-19 is that people who are infected can transmit the virus five days before they experience any symptoms. (For other respiratory viruses, including the flu, sick people are only contagious 24 hours before experiencing symptoms.) A study published in the journal Nature estimates that 44 percent of all infections occur before the sick person realizes they have the virus.

This is the main reason why socially distancing in public is so important. It also means screenings and temperature checks are less effective at preventing the spread of the virus.

Some of the most eye-opening research on how COVID-19 spreads comes from analyses of what scientists are calling “super-spreader events”—gatherings where a large percentage of attendees contract COVID-19. A study published by a Chinese public health organization found that the air-conditioning system in a restaurant in China helped to spread the virus to ten different customers eating there. Another account describes how the virus spread through a small town in Georgia after an infected person attended a funeral there. The vast majority of these super-spreader events take place indoors, where ventilation is poor and people are packed closely together.

So, as people return to gathering—although in more limited ways—what steps can they take to avoid contracting COVID-19?

Masks might help. Handwashing is certainly effective.

A systematic review published in 2011 combines data from 67 studies to answer the question, do physical interventions, such as masks and handwashing, help to prevent the spread of respiratory viruses?

(It is important to note that this review does not include any information about the current pandemic, but does provide some information about how respiratory viruses spread.)

The review found high-quality evidence that handwashing is effective at preventing the spread of respiratory viruses, especially among young children.

It offers limited evidence that using masks helps prevent the spread of respiratory viruses, and that N95 masks are more effective than regular surgical masks, especially in hospital settings. But the review does not include evidence about wearing non-medical masks in community settings, such as grocery stores or workplaces. It also finds that global interventions, such as screening visitors at entry ports, lead to a small delay in the spread of the virus, but the data are not significant enough to draw a strong conclusion.

A newer systematic review published at the end of April includes evidence specifically related to the current pandemic. It combines the evidence from 19 randomized, controlled trials—the gold standard of medical research. Eight of the trials were conducted in community settings, six in health care settings and five related to source control of the virus.

In community settings, the review found that wearing masks and hand-washing together are the most effective virus control strategies. In healthcare settings, it found that respirators are effective in reducing disease transmission, but only if worn continually during a shift, and masks are much less effective. It also found that when individuals who are sick with coronavirus wear a mask, it reduces the likelihood they will infect someone else.

The take-home message: Scientists are still learning about how COVID-19 spreads between people. By taking a careful look at how the disease has spread in the past and evaluating interventions put in place to date, they are building a clearer picture of the best ways to prevent the transmission of COVID-19. To date, there is some conclusive evidence that wearing masks when out in public and frequent handwashing are your best bet to help limit the spread of the virus. Avoiding prolonged time indoors with large groups of other people may also be an important way to avoid contracting COVID-19.

Visit Cornell University’s Bronfenbrenner Center for Translational Research’s website for more information on our work.