What should I do if exposed to Covid?

If you're vaccinated, the risk of infection for a single exposure is low but noticeable

This is part of a collection of articles on Covid-19

In my last post, I discussed what to do if you get Covid. Here, I'll briefly discuss what to do if you were in close contact with someone with Covid.

First, I'll say that if you're an average person, you should just assume that at some point in January you most likely have been or will be exposed. The exception would be basically if you're staying at home and avoiding nearly all contact with people (i.e. lockdown bubble).

Second, being exposed very much does not guarantee that you'll be infected - the chances of infection for a given exposure are low, especially if you're boosted. So if you've been exposed, you should still continue to take precautions against getting Covid.

Let's say you were in close contact with someone who tests Covid-positive, indoors, for one hour. Your baseline risk of infection if you're vaccinated and boosted is about 3-4% per hour. If you were masked or distanced, your risk is reduced by the usual amounts, see microcovid.org or my Covid risk analysis article. On microcovid, you can model the situation and set "Risk Profile" to "Has COVID" to estimate the chance that you get Covid from this exposure.

To understand that number, you can compare that to how much your normal risk of Covid is on a weekly basis, or compare it to the number of microcovids of an average person in your area. Before the Omicron surge, it might be typical that a close contact means you are e.g. 20x more likely to have Covid in the next week than normal - so stronger precautions to avoid potentially spreading Covid in case you did get infected may be worth it to you and those around you. But with the Omicron surge the average person's baseline risk is so high that any one exposure does not increase it all that much - e.g a close contact might double your risk of being Covid-positive in the next week. (This doesn't necessarily mean it's less important to take precautions if you do get exposed - the absolute risk is still the same - but the relative increase in precautions you should take if you are vs are not exposed is less.)

CDC guidance says that if you're vaccinated and boosted, you should wear a high-quality, well-fitting mask (N95 or similar) when near others, for 10 days from your close contact with someone with Covid, and you should get tested around 5 days after your close contact, but that you don't need to quarantine. (Close contact is defined as being within 6 feet for at least 15 cumulative minutes.) This seems pretty reasonable to me overall if you know you were in extended, close contact indoors, and you're vaccinated and boosted, although I would adjust based on the level of risk of the exposure as discussed above. If it was hours and without precautions you may want to self-quarantine until you can get a negative test, for example. If for example it was 15 minutes and you were wearing high-quality masks, then the additional risk may not be significant compared to the average person’s risk during the Omicron surge.

Regarding testing: tests take a couple days after you’re infected before they start returning positive results - see this diagram for an idea of the timeline of infection, symptoms, and test results. PCR tests will start returning positives earliest, and rapid antigen tests may take a couple additional days, probably around 2 days. However, the days before the rapid tests return positive results also tend to be relatively low infectiousness, while your viral load is still low. I think rapid tests are still a good but not perfect correlate to the days when your infectiousness is high. Should you also swab your throat when taking a rapid test for Omicron? | Brunch At Eleven suggests that swabbing both your nose and throat may help detect Omicron earlier.