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

The BA.5 subvariant of Omicron dominated COVID-19 case counts in the U.S. in 2022. While BA.5, like previous Omicron subvariants, seems to spread more easily than other COVID-19 variants, the symptoms have generally been milder and have a shorter duration of six to seven days.

But despite being more than two years into the COVID-19 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. Here's what to know about the Omicron variant.

A Milder Variant

Generally speaking, Omicron and its subvariants cause more mild disease than previous variants like Delta. In fact, according to an August 2022 study published in JAMA Network Open, over 56% of people who were likely infected with Omicron didn't know they even had the virus.

But that doesn't mean it's completely harmless for everyone. Some people 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 Omicron may be somewhat milder, it spreads more easily than earlier variants, including the Delta variant. Anyone with Omicron infection, regardless of vaccination status or whether or not they have symptoms, can spread the virus to others. In addition, Omicron can cause reinfection, even in people who have recovered from COVID-19.

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 have been vaccinated or 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 a December 2021 report published in the CDC's Morbidity and Mortality Weekly Report (MMWR),

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, Dr. Adalja said.

The shortened incubation period also means that people may test positive sooner, due to emerging symptoms. According to guidelines from the CDC, 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 48 hours after the first negative test, for a total of at least two tests, says the Food and Drug Administration (FDA). If you have a negative result on the second test and you are concerned that you could have COVID-19, you may choose to test again 48 hours after the second test, consider getting a laboratory molecular-based test, or call your healthcare provider.

Omicron Symptoms and 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," Dr. Adalja said. 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), Dr. Adalja added.

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, headache, congestion, and runny nose.

Research published in April 2022 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. According to a May 2022 study published in the journal Otolaryngology — Head and Neck Surgery, compared to rates of smell and taste loss during the early phase of the pandemic in 2020 before variants were identified, chances of smell and taste loss were just 17% for Omicron, 44% for Delta, and 50% for the Alpha variant.

And while some reports say gastrointestinal symptoms are also more common with Omicron than previous variants, evidence from the ZOE COVID-19 Study suggests GI issues were just as prevalent with Alpha and Delta.

How Long Do Symptoms Last?

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, the length of symptoms varies greatly depending on the person, their vaccination status, the severity the 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," Dr. Adalja said.

Despite these often less severe symptoms and the 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 healthcare 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: If you test positive, regardless of vaccination status, you should isolate at home for five full days. You should also isolate if you are sick and suspect that you have COVID-19 but do not yet have test results.

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," MacDonald said.

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," MacDonald said. That's not to say there is no risk, MacDonald 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.

If you have access to antigen tests, you can test yourself. With two sequential negative tests 48 hours apart, you may remove your mask sooner than day 10.

For people who developed severe illness from COVID-19 or have a weakened immune system, the CDC recommends consulting your healthcare provider before ending isolation. Ending isolation without a viral test may not be an option for you.

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.

Immunity After Omicron

It's important to remember that Omicron and its subvariants are still relatively new iterations of COVID-19—which means that experts are still gathering information on how much immunity is conferred after infection.

"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," Dr. Adalja said.

It also looks like vaccination plus previous infection work together to boost immunity from an Omicron infection. Research published in the journal Nature in May 2022 showed that an Omicron breakthrough infection—which happens when a previously vaccinated and/or boosted individual gets Omicron—enhances immunity.

However, the evidence is not clear about how protective Omicron infection is for future infections. A June 2022 study published in Science concluded that people infected with the Omicron variant show poor immunity boosting against future COVID-19 infection.

The research team analyzed blood samples from 731 U.K. healthcare workers who received three doses of mRNA vaccine and had different SARS-CoV-2 infection histories, to investigate immunity against Omicron.

The researchers found that people with no prior COVID-19 infection who then had Omicron showed enhanced immunity to previous variants but a reduced boosting against the Omicron spike protein itself.

Study co-author Danny Altmann from Imperial College London told the British Medical Journal that Omicron is "an especially stealthy immune evader. It's more stealthy than previous variants and flies under the radar, so the immune system is unable to remember it."

However, a later study reported in Nature in July 2022 suggests that, while the Omicron BA.4 and BA.5 subvariants may be stealthier at evading the immune system than all of their predecessors, a prior Omicron infection is substantially more effective to protect against reinfection than any previous COVID-19 variant.

Specifically, the researchers reported, prior infection with Omicron was 79.7% effective at preventing BA.4 and BA.5 reinfection and 76.1% effective at preventing symptomatic reinfection.

The study evaluated all of Qatar's COVID-19 cases since the wave of BA.4 and BA.5 infections began.

Overall, experts believe 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," MacDonald said.

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.