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Dr. David Hamer, a professor of global health and medicine, explains why rapid tests are effective at indicating when someone is infectious.

Corona rapid tests with negative results in Dortmund, western Germany. INA FASSBENDER/AFP via Getty Images

In the wake of the omicron wave, the steps to take after being exposed to COVID-19 seem increasingly complicated. If someone gets exposed, do they test immediately? Or do they test after 5 days? Should they isolate for 5 days? Or 7? Or even 10? 

Below is a timeline of what to do after being exposed to omicron and what should be done at each juncture with the help of Dr. David Hamer, a professor of global health and medicine at the Boston University School of Public Health and School of Medicine. 

Right after being exposed: 

First off, don’t get tested right away. 

“With omicron there’s at least a suggestion that you become infected and symptomatic within two or three days.” said Hamer. “If you have had no symptoms and no other exposure, testing the same day as an exposure is a waste of time.”  

3-5 days after exposure: 

Get tested.

According to the most recent Center for Disease Control guidelines, if someone exhibits symptoms of COVID-19, they should get tested. Therefore, over the 3-5 days following exposure, that person should be monitoring for signs of symptoms.

However, if they still don’t have symptoms five days after exposure, they should still seek out a test to check if they are infected and asymptomatic. 

What symptoms to look for within those 3-5 days: 

The symptoms associated with omicron are slightly different than previous variants, aligning more with influenza or the common cold according to Hamer. Someone with omicron can expect to experience symptoms like those listed below: 

  • Runny nose
  • Headache
  • Fatigue
  • Sneezing
  • Sore throat

This is according to the Zoe COVID-19 Symptom Study. 

What kind of test to get and why: 

During Governor Baker’s Jan. 11 press conference concerning testing and exposure, he emphasized that rapid tests are a reliable way to get results. 

This is because of something called viral load. 

Hamer explained viral load as “the concentration of virus in some bodily fluid.”

Rapid tests are a strong option because they are quick, cheap, easy to find and use, and can usually tell someone that — not only are they positive — but also infectious.

A PCR test will indicate a positive result if someone has “really tiny particles” of virus left in their system, according to Hamer. However, rapid tests will only show a positive result if there is a large amount of virus concentrated in the body, enough to make that individual clearly infected and infectious.

When someone is initially infected with COVID-19, said Hamer, they are likely to be infectious because there is a large amount of virus in the body. However, as that infected person starts to recover, their viral load quickly decreases.

“SARS-CoV-2 is a virus that grows quickly inside the body, so by the time a benchmark PCR test becomes positive, the virus is well into exponential growth,” read a study published in the New England Journal of Medicine. “At that point, it is probably hours, not days, before the virus grows by orders of magnitude, reaching the detection thresholds of currently available cheap and rapid point-of-care tests.”

For a more visual interpretation, the New England Journal of Medicine created a graph. 

“[A rapid test] does tell you that you’re infected, but also, it has a pretty good association or sort of correlation with infectiousness,” Hamer said. 

Graph from Rethinking Covid-19 Test Sensitivity — A Strategy
for Containment.

After testing positive: 

Current CDC guidelines recommend isolating for five days. However, Hamer has thoughts. 

“The CDC recommends five days. It’s not based on a lot of evidence…day five about half or less people are no longer infectious, and by the seventh day it’s gone down to an even better, lower level of risk.” 

Hamer recommends abiding by the official isolation guidelines, but advises it’s good practice to continue wearing a well-fitted mask for a few days beyond the five-day mark.

Why it’s not suggested to get a PCR test to return to normal activity: 

“The PCR is much more sensitive, so it can detect really tiny particles of the RNA of the virus.” he said, “Some people will have bits and pieces of virus spread that goes out for weeks.”

Therefore, getting a rapid or even an at-home test to provide to workplaces, schools, and other facilities is a much better method. This is also why most organizations that do mandatory testing of their community, such as universities, will exempt those who have already been infected from the testing requirement for 90 days. 

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