They’re able to detect smaller quantities of the virus and detect them sooner (and for more time) than antigen tests. PCR tests are far more sensitive than antigen tests. That’s why I tell people they should trust a positive antigen test, but be more skeptical about a negative one. That’s why if someone has COVID-19, but hasn’t yet reached the test's threshold of viral particles, they may still test negative with an antigen test but positive on a polymerase chain reaction (PCR) test. But a negative antigen test doesn’t necessarily mean you aren’t contagious. Rapid antigen tests detect COVID-19 when people have a higher amount of virus particles in their system and are more contagious. Rapid antigen tests, which you can buy in most pharmacies, are great in specific circumstances and less good in others.
Q: How are rapid antigen tests different from PCR tests? Is one better than another? Stay isolated if you have any symptoms, even if you cannot quickly get a COVID-19 test. People who are unvaccinated or immunocompromised may still get severe disease. Even if you have minor symptoms, you are still contagious. Symptoms may include sniffles, congestion or a cough, and might resemble a mild cold, especially in fully vaccinated and boosted people. Isolate and get a COVID-19 test if you have ANY symptoms of COVID-19, even if they’re mild and even if you’re fully vaccinated and/or boosted. As an infectious diseases expert and a hospital epidemiologist, here's what you should know about when to get a COVID-19 test, what kind you should use, what to do if you can't get one at all and why it's still important to get vaccinated and boosted. As case counts surge, so does demand for testing. As the Omicron variant of COVID-19 surges around the country, we're seeing increases in infections, even among people who've been fully vaccinated and have what are called breakthrough infections.