Omicron Infection Timeline: When Symptoms Start and How Long They Last

Here's how the illness typically unfolds, from beginning to end.

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Fact checked on June 3, 2022 by Vivianna Shields, a journalist and fact-checker with experience in health and wellness publishing.

Two subvariants of Omicron—BA.2 and BA.2.12.1—are currently dominating COVID-19 case counts in the U.S. But despite being more than two years into the coronavirus pandemic, there's still some confusion as to what having COVID-19 looks like from start to finish, especially as new variants and subvariants continue to pop up.

Generally speaking, Omicron and its subvariants cause more mild disease than previous variants like Delta—but that doesn't mean it's completely harmless for everyone. Some people, particularly those who are unvaccinated, are still at risk for severe disease, hospitalization, or even death. Breakthrough infections, too, are expected to occur with Omicron and its subvariants.

And while the Omicron may be somewhat milder, its subvariants have gotten increasingly more contagious: BA.2, which began its rise in late-February and early-March, was estimated to be about 30%–60% more transmissible than its predecessor, BA.1. And now, BA.2.12.1—the new dominant Omicron subvariant in the U.S.—is thought to be about 25% more transmissible than that.

Omicron and its iterations likely aren't going away anytime soon, and you may still contract the virus (although likely a milder version) even if you've been vaccinated, boosted, or have had a previous case of COVID-19. In that case, here's what a typical timeline of an Omicron infection looks like, from exposure to immunity.

Incubation Period and Testing

Omicron and its subvariants have shorter incubation periods, which means it takes less time for symptoms to appear after exposure to the virus.

"Omicron has the shortest incubation period that we've seen," infectious disease expert Amesh Adalja, MD, a senior scholar at the Johns Hopkins University Center for Health Security, told Health. That incubation period is just about three days, compared to the Delta variant's five-day incubation period, and the original SARS-CoV-2 virus' incubation period of more than 5 days.

According to Dr. Adalja, Omicron's short incubation period may be influenced by built-up immunity from the past two years. Much of the population has been exposed to COVID-19 at one point or another—via vaccination or prior infection—which means their immune systems are already primed to jump into action more rapidly. How soon symptoms occur is directly tied to when your immune system recognizes and responds to the virus, said Dr. Adalja.

The shortened incubation period also means that people may test positive sooner, due to emerging symptoms. According to guidelines from the Centers for Disease Control and Prevention, you should test as soon as you begin feeling any cold- or flu-like symptoms. If you test negative but continue to feel ill, you can test again one to two days later, or talk to a health care provider about taking a PCR test, which is typically more sensitive. If you've been exposed to COVID-19 but don't develop symptoms, the CDC suggests testing five days after exposure.

Symptom Onset

Because of Omicron's shortened incubation period, those who are infected will begin to show symptoms sooner, if they're symptomatic. Most of the time, particularly because Omicron tends to be less severe, a case may look a lot like the common cold, or even allergies.

"As your body starts recognizing the fact that it's been infected, your immune system will start taking actions, and those actions are those symptoms that you feel: fatigue, headache, malaise," said Dr. Adalja. People may not test positive during these initial symptoms, simply because there isn't enough virus in the body to show up on a test (though there is enough to make you feel unwell), he said.

Though symptoms of Omicron aren't drastically different from those associated with the Delta variant, they are manifesting differently, Pia MacDonald, PhD, MPH, an infectious disease epidemiologist at RTI International, told Health. The most commonly-reported symptoms with the original Omicron variant were cough, fatigue, congestion, and runny nose. Research published in The Lancet also found that sore throat and hoarse voice were consistently more prevalent with Omicron infections than with Delta.

Meanwhile, loss of taste and smell, which was a common symptom with previous variants, is less likely to occur with Omicron. And while some reports say gastrointestinal symptoms are also more common with Omicron than previous variants, evidence suggests GI issues were just as prevalent with Alpha and Delta.

One thing that can drastically reduce symptom severity in people with Omicron is prior vaccination and booster doses. "This is a huge difference among vaccinated versus unvaccinated [people] in terms of severity of disease for an infected person," said MacDonald. "Even with the newer Omicron variants, being vaccinated and boosted is very protective for severe infection, hospitalization, and death."

As far as how long these Omicron symptoms last, research shows that people have acute symptoms for about six to seven days—about two days shorter than Delta's eight to nine days of acute illness. That said, length of symptoms varies greatly depending on the person, their vaccination status, the severity of disease, and any risk factors. "In general, the fact that Omicron is occurring in a highly-immune population should diminish the symptoms because the virus is able to clear faster," said Dr. Adalja.

Despite these often less severe symptoms and potentially reduced symptom duration, it's still essential for those who are at high risk of severe illness from COVID-19 to check in with a health care provider if they contract the virus. This way, they can potentially get a prescription for Paxlovid, an antiviral medication used to help prevent severe illness from the disease. While some people have reported 'Paxlovid rebound'—or a recurrence of COVID-19 symptoms after they've finished their course of treatment—those rebound symptoms tend to be mild and only last a few days.

Isolating With Omicron

The CDC has some pretty specific rules centered on isolation time with COVID-19, regardless of the variant (for now): If you test positive or are showing symptoms, regardless of vaccination status, you should isolate at home for five full days.

It's during that time when people typically have the highest viral load and are most contagious. "The average peak is going to be on day two from when it was detected via a test," said MacDonald.

After the five-day mark, people may start easing up on isolating. "After five days of either being detected on a rapid test or after symptom onset, your chance, your risk of infecting others is dramatically decreasing after five days," said MacDonald. That's not to say there is no risk, she added, just that the odds of spreading it is much, much lower.

If you remained asymptomatic for your illness, you can end your isolation after five days, but continue to mask around others for another five days. If you developed symptoms, you may also end your isolation after five days (and continue to mask for another five days), as long as your symptoms are improving, and you've been fever-free for 24 hours.

For people who developed severe illness from COVID-19 or have a weakened immune system, the CDC recommends isolating for a full 10 days, and possibly up to 20 days. That's because infectiousness declines much more quickly in immunocompetent people, according to MacDonald. Immunocompromised people may have a harder time clearing the infection and can therefore stay contagious longer.

Though the CDC doesn't outright recommend people test out of isolation, the agency does suggest that if you have access to an at-home test, the best approach is to test at the end of the initial five-day isolation period. If a positive test results from that, you should isolate until day 10.

Immunity After Omicron

It's important to remember that Omicron and its subvariants are still relatively new iterations of COVID-19—which means that there's not a lot of data on how much immunity is conferred after infection. But health experts still have some ideas.

"If you got infected with any of the versions of Omicron there is probably good cross-protection of BA.1 and BA.2—and maybe less so with BA.4 and BA.5—but for the immediate period of a couple of months to several months after infection, it's unlikely that you'll get [re]infected," said Dr. Adalja said.

It also looks like vaccination is a key factor in how much immunity one can get from an Omicron infection. New research published in the journal Nature shows that an Omicron breakthrough infection—which happens when a previously vaccinated and/or boosted individual gets Omicron—enhances immunity. But Omicron infection in unvaccinated people may not provide much protection against non-Omicron variants.

Overall, experts believe that immunity through vaccination is more robust than immunity through previous infection alone—and that the most robust protection is through vaccination and boosters, which means it's important "to not rely on natural immunity to be highly protective for Omicron," said MacDonald.

And even with a certain level of immunity—whether it's from just an Omicron infection, or from an Omicron infection plus prior vaccination—it's still important to monitor and follow CDC guidelines depending on your community's risk level. While people may choose to mask at any time, it's still recommended that people in high-transmission areas remain vigilant and mask indoors in public.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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