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Ahead of Christmas, health experts suggested undergoing a rapid coronavirus test just before any gatherings.

But some health experts are now warning that you can test negative even if you’re infected and contagious while still being visibly healthy.

In general, tests are able to reveal an Omicron infection, but enough virus needs to have reproduced and appear at sufficiently high levels in the nose or saliva to be detectable, according to Dr. Michael Mina, an epidemiologist and former professor at the Harvard T.H. Chan School of Public Health, whose interview on the podcast “In the Bubble,” hosted by former White House COVID-19 advisor Andy Slavitt, published this week.

“Omicron does appear to be more infectious, so it might be taking off and actually spreading the first day or two before there’s enough virus in your nose to turn the [rapid] antigen test positive — or the PCR test positive, for that matter,” Mina said on the podcast. “You might already be infectious, and that’s potentially because the virus now is just so able to potentially aerosolize and get out of people at lower amounts.”

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