I have COVID-19 but am not sick. Can I give it to others?

(Note: references and additional reading are in notes at the bottom for those who would like them.)

Short answer: Yes.

Long answer: We’re still learning a lot about COVID-19 and the virus that causes it (SARS-CoV-2). One key question is: “What is the role of people who are infected with the virus but don’t have symptoms?” A number of studies have been shared in the last week that help us answer that question.

We know that lots of people with COVID-19 don’t have symptoms. Estimates vary, but using data from the Diamond Princess cruise ship and China it looks like 20-40% of people with COVID-19 won’t develop symptoms.(1) However people who are infected might still be contagious. We are seeing more and more evidence this happens with COVID-19.(2) While we are still debating the amount that people without symptoms are contributing to the overall spread of COVID-19, it's pretty clear that they do play a role.

So what do we do with this information?

If people without symptoms can transmit the virus, COVID-19 is going to be much harder to control than many of us had initially hoped. The measures we need to flatten the curve in this situation aren’t that different from what we are already doing but our margin for error diminishes substantially. We need to make sure we do these things very, very well for a long time (probably 12-24 months):

• Stay home and quarantine if you or anyone in your household is diagnosed with COVID-19. If one of your close contacts is diagnosed with COVID-19, assume that you have it too even if you feel fine. Given that testing is still so limited, I think it is appropriate for anyone with cold or flu symptoms, and their close contacts, to act as if they have COVID-19 and self-quarantine.
• If you are in a high risk group, reduce your contact with other humans as much as possible. You might still need to go to work or to the store to buy groceries, but work with your employer and your community to minimize you contact with others when you do these things.(3) Please ask for help if you need it. This is not only to benefit you. It’s to benefit all of us.
• Even if you’re not in a high risk group, reduce your contact with other humans as much as possible. Go to work if teleworking isn’t an option for you, but do your best to minimize your contact with others. If you're young and healthy, you might think you can't get sick and there is no reason for you to do social distancing. This is not true. You can still get severe COVID-19 infection and die. You also put others in danger if you get sick.
• Don't hoard medical supplies or toilet paper!(4)

A scary and hard reality is that even if we do all of this, COVID-19 will still hit us hard (5) but we still have some control to decrease how hard it hits. If we work together on this, we can save lives.

Notes:

(1) Mizumoto et al; Nishiura et al

(2) Case reports: Bai et al; Cai et al; Tong et al. Clinical studies: Woelfel, et al; Hu, et al; Shi et al; Pan et al; Hoehl et al; Zou et al. Epidemiologic observational studies: Hu, et al. Modeling studies: Ganyani et al; Nishiura et al.

(3) Many people, organizations, and businesses are trying hard to support people who are high risk for severe COVID-19 illness. In Seattle, many stores have designated hours for high-risk individuals to shop. Mutual aid organizations are appearing all over the world. Find the one near you to get extra support.

(4) Some of you are probably wondering if we should all be wearing masks since people without symptoms can spread the virus. At this point, we still don't have evidence that everyone wears masks is helpful. That is something that will need to be considered and studied, but at the moment we don’t have enough masks to go around even for the people who definitely need them under the current guidelines. For now, please continue to leave masks for people who are sick and for healthcare workers.

(5) Ferguson et al. did an extremely well thought out modeling study examining the impact of these different interventions. The paper is technical but it’s very clearly written and many should be able to follow a good portion of it. The findings are sobering and can be scary but this is the reality we’re facing.