Only one more COVID-19 Quarantine ’til Christmas

Lucy D’Agostino McGowan, Elizabeth Lee, and Justin Lessler

Christmas is officially 14 days away (yay!), which happens to be one coronavirus quarantine. Many are likely considering attempting to quarantine before gathering to reduce the risk of COVID-19 this season. While avoiding gathering is the best way to keep you and your loved ones safe this year, a 14 day quarantine prior to gathering for all people involved can help reduce the risk.

Quarantining is one tool in your toolkit for making gathering with people outside your household safer. Not everyone will be able to use this tool, for example healthcare and other essential workers or those on an hourly wage are often not able to limit interactions outside their household for weeks in a row. Additionally, for this tool to be maximally effective, everyone planning to gather needs to quarantine; those participating in “bubbles” should take a pause from close encounters with people outside their household, since we know that bubbles are often larger than we think. For those that are able to, the following is a short explainer on the thought process behind quarantining and why at least a 2 week quarantine for all parties involved is ideal before getting together with folks outside your household.

Why 14 days? The main idea behind 14 days is if you are infected, you are likely to notice (start having some symptoms) within two weeks, so you can cancel your plans before you accidentally spread the virus. Since the beginning of the pandemic, scientists have been collecting data on the number of days from when someone is infected until they show symptoms. They can then plot this data and look at the shape to gain an understanding of the incubation period.

There have been lots of studies that do this, and all of them show a pretty similar shape, with a peak at 4–7 days and a tail that extends out at least 2 weeks. Combining all of the data from all of these studies gives an even better estimate for the time from when someone is infected to when they first show symptoms.

We can change how we look at this data to make it easier to see cumulatively how many people saw symptoms by a certain day. For example, if we add up all of the people who showed symptoms by day 10 and divide by the total number of people, we would see that 91% of people show symptoms by day 10. Doing this across all days helps us know what percent of infected folks will see symptoms by a certain time. The shape across all days looks like this.

About 98% of infected people will notice they are infected within 14 days, which is why this is the recommended time to quarantine.

What about a 10 day quarantine? A 10 day quarantine is better than not quarantining at all (and also better than a 9 day quarantine!) but based on what we know about the incubation period, about 9% of infected folks won’t see symptoms until more than 10 days after getting infected. A 10 day quarantine with a negative test is better than a 10 day quarantine without one.

What about a 7 day quarantine with a negative test? Again, a 7 day quarantine with a negative test is better than not quarantining at all (and better than a 7 day quarantine without a negative test) but keep in mind that even our best tests have a hard time accurately detecting whether you are sick before you start showing symptoms and over a quarter of infected folks won’t see symptoms until more than 7 days after getting infected. Getting a test as close to the gathering date as possible will help to decrease your chances of seeing a false negative result.

So what does this mean for me? Consider the amount of risk you are willing to take on behalf of yourself and your loved ones. The data here highlight one aspect of this, estimating the risk of realizing you were sick after gathering if you were infected a certain number of days prior. It is important to think about the vulnerability of those involved when making these decisions. We know that age is a crucial risk factor for COVID-19, for example your 80 year old grandpa has a greater than 10% chance of dying, should they become infected. If gathering with high risk individuals, extra caution is warranted. That being said, here are 4 main takeaways:

1. If you plan on gathering with folks outside your household on December 25th, a 14 day quarantine starts today. This means, if you are infected now and going to get sick, you have a 98% chance of seeing symptoms before Christmas, allowing you to cancel your plans before infecting anyone else.
2. If a 2 week quarantine isn’t possible for all people involved, each person should quarantine for as long as is feasible prior to gathering — every additional day helps!
3. If you are able to get a test, try to get the test as late as you can (with enough time to receive the test result before gathering).
4. Nothing is perfect. If you want to be as safe as possible and maximize your chances of you and your loved ones not getting sick before they can get vaccinated, skip the holiday gathering all together.