How to tell the difference between the common cold, flu and COVID-19

As colder temperatures set in for many U.S. states, the uncertainties of the ongoing COVID-19 pandemic continue to linger, leaving many people still wondering if the cough and aches they feel are actually due to the flu, common cold or the novel coronavirus.

Despite the wide availability of COVID-19 vaccines to Americans as young as 5 years old, the chance of infection from COVID-19 is still a possibility. So how do you tell the difference between the flu, the common cold or COVID-19? 

Jade Flinn, a nurse educator at Johns Hopkins Hospital’s biocontainment unit, outlines some key differences and similarities between the three illnesses.

Symptoms of cold, flu and COVID-19

Some common symptoms of a cold, the flu and COVID-19 can include but are not limited to fatigue, cough, headaches, fever, stuffy nose, sore throats, aches and chills. 

A key difference between a common cold and both the flu or COVID-19 include the following symptoms:

• Both the flu and COVID-19 can lead to fever, cough, body aches, and sometimes vomiting and diarrhea (especially in children)
• Flu and COVID-19 can result in pneumonia
• Both the flu and COVID-19 can be asymptomatic, mild, severe or even fatal

"The biggest thing (similarity) is all the schmutz that’s coming out of your nose. That’s the runny nose, the post-nasal drip, the sore throat, the coughing. That can pretty much be the common cold, the flu or COVID," Flinn told FOX TV Stations.

"The biggest difference, I think, are what we are trying to target. So with COVID, one of the tell-tale classic signs that people talk about is that loss of taste or smell, which typically you don’t see with flu or you don’t see with the common cold," Flinn added.

Flinn said a typical sign when it comes to COVID or the flu is having a fever. 

"With colds, you typically don’t have that fever unless you’re really, really sick. And the people that do get sick from the common colds are those who are predisposed to things like chronic medical conditions, they’re immunosuppressed, they might have kidney or lung disease so things like that would make them have more severe illness and symptoms compared to a healthier person," Finn continued." 

The time to seek immediate medical attention for either COVID-19 or the flu is if you start experiencing shortness of breath, Flinn said. 

"Getting that shortness of breath, that chest pain, all of that," she explained. 

"As far as the mild symptoms, the same kind of symptoms that you would have with a cold — the runny nose, the post-nasal drip, the cough, the sore throat. If any of these are to the point where you cannot get out of bed and you can’t really care for yourself, you feel that you’re getting dizzy, that’s the time that I would seek emergency medical assistance," Flinn suggested. 

As the omicron variant of COVID-19 continues to raise concerns across the world, Flinn said what health experts have seen so far is that particular strain is eliciting more mild symptoms in those who have been infected.

RELATED: Omicron variant now makes up about 3% of US COVID-19 cases, CDC says

"From what I have heard, most cases that we’ve heard of the omicron virus, is that its more mild symptoms but what we’re concerned about is, is this more transmissible than what we’ve seen with delta? If it’s more transmissible, are we seeing any changes in the vaccines’ effectiveness against that," Flinn posited. 

The U.S. Centers for Disease Control and Prevention said on Dec. 13 that while the delta variant remains dominant, the omicron variant represented 2.9% of sequenced U.S. cases last week, up from 0.4% during the previous week.

CDC Director Dr. Rochelle Walensky said omicron appears to be more transmissible than previous strains of the virus and has now been detected in 33 U.S. states and in 77 countries worldwide.

"While it is rapidly increasing, we have the tools needed to fight #COVID19. Get vaccinated, get boosted," Walensky wrote in a tweet.

The omicron variant has been driving a surge in infections in South Africa, where it was first identified by scientists. A large-scale analysis of data from the country

, released on Dec. 14, showed that the new variant seems to be more easily spread from person to person and better at evading vaccines — but also milder.

RELATED: Omicron variant is milder but better at evading vaccines, South African data indicates

When symptoms appear for COVID-19, flu, cold

COVID-19

Typically, a person experiences symptoms about five days after being infected, according to the CDC. However, symptoms can also appear 2 to 14 days after infection.

Flu

A person infected with the flu experiences symptoms anywhere from 1 to 4 days after infection.

Common cold

A person can start seeing symptoms from a common cold between 1 to 3 days after infection. 

"One of the bigger differences that you may see also is when did these symptoms start? With a cold, typically it takes 48 hours. You may have been exposed over the weekend and then by Tuesday you’re like, ‘I don’t feel well.’ So we typically look at when were you exposed and then when did your symptoms start. If it’s kind of at that five-day period, that’s when we start getting concerned about COVID," Flinn said. 

"With common colds as well as with flu, typically you are contagious maybe one day before you’re symptomatic. And with COVID, we’ve had that same thing, we have asymptomatic spreaders. And it’s really difficult to really categorize everyone into ‘you’re really contagious,’ but everyone knows that you’re contagious or infectious when you are showing those symptoms because you’re producing more respiratory droplets," Flinn said, adding that preventative measures like hand washing and staying home when you're sick are key. 

COVID-19 has been a wild-card when it comes to the onset of symptoms as they can start showing up anywhere between 2 and 14 days, according to Flinn. And some people who have become infected may be asymptomatic but still risk spreading the virus. 

The CDC has recommended the 10-day rule for people who were infected with the virus and tested positive. The rule basically advises that those who were sick with COVID-19 should wait at least 10 days from the last time they felt any symptoms or had a fever before resuming normal activities and start going around people. 

And for those who are immunocompromised, it could be beneficial to extend the 10 days to 14 days or even three weeks, Finn said. 

"And sometimes if you’re more immunosuppressed, maybe a 14-day or maybe even a three-week window. And it’s really how effective is your body at creating those antibodies and then are you shedding that virus that’s still viable in infecting others," Flinn advised.

"Fortunately with the flu and the common cold, we have a shorter window where we’re sick and showing symptoms. So as a rule of thumb, if I’m showing symptoms with a flu or cold, typically after 48 hours from the last time that I had a fever or I’m really feeling sick, then I can say, ‘OK, maybe I can start coming around people,’" Flinn added. 

Transmissibility of cold, flu and COVID-19

Transmission of the common cold is far less likely since most people who are suffering from a cold tend to only be contagious the first two or three days of having it, according to Children’s Health Los Angeles. 

However, the flu and COVID-19 are far more transmissible. Usually, the flu can be contagious anywhere between the first day and the fourth day of infection, whereas COVID-19 can be contagious between the second or fourth day before symptoms appear, according to the CDC. But with COVID-19, a person can be contagious without having any symptoms which is also known as being asymptomatic. 

COVID-19 vs. flu

• Both can spread through droplets or smaller virus particles from a sick person to other people nearby
• Smaller particles may linger in the air, and another person can inhale them and become infected
• Both viruses can contaminate surfaces and infect a person who has touched it

"We’ve seen that COVID typically is a bit more transmissible across people. But as far as the transmission way, it’s the same. It’s through those respiratory droplets, it’s through close contact with someone, touching the same things that maybe haven’t been cleaned and then touching your eyes. Any of those portal of entries. So, those same precautions that we were doing with COVID, were also helping reduce your exposure and infection with common colds and for flu," Flinn said. 

People most impacted

While all humans have the potential to get sick, there are groups of people who may be more at risk for contracting COVID-19, the flu and the common cold.

• Older adults
• People of any age with chronic medical conditions (such as chronic cardiac, pulmonary, renal, metabolic, neurologic, liver or hematologic diseases)
• People with immunosuppressive conditions (such as HIV/AIDS, patients receiving chemotherapy or steroids, or malignancy)
• Pregnant women
• Younger children

Prevention

For either COVID-19, the flu or even the common cold, the best way to prevent spreading any of these illnesses is the same: isolate, mask up and wash your hands, Flinn advised. And get vaccinated for either COVID-19 or the flu. 

"Especially with those who would be more severely ill, even catching the common cold or the flu, that could put them in the hospital — which puts more pressure on the healthcare system overall," Flinn said. "This COVID-19 pandemic has really opened our eyes to say, ‘Hey, we should be treating all of these as seriously as we have with COVID.’" 

Treatment options

COVID-19

Some FDA-approved monoclonal antibody treatments can be used to treat patients already infected with the novel coronavirus, according to Johns Hopkins. But the treatments need to be initiated early in the course of COVID-19. 

Currently, effective treatments are only available in an intravenous form, so they are not prescribed to patients outside of a hospital setting.

Separately, an influential panel of outside advisers to the U.S. Food and Drug Administration met on Nov. 30 and endorsed an experimental drug by Merck that could soon become the first U.S.-authorized pill for patients to take at home to treat COVID-19.

The FDA’s Antimicrobial Drugs Advisory Committee is made up of academics and other experts reviewing its safety and effectiveness. The FDA asked its outside advisers whether the agency should authorize the pill, weighing new information that it is less effective than first reported and may cause birth defects.

The panel’s recommendations aren't binding but often guide FDA decisions.

Additionally, Pfizer’s experimental COVID-19 antiviral pill appeared to be effective against the omicron variant, according to an announcement made by the company on Dec. 14.

Pfizer also said full results of its 2,250-person study confirmed the pill's promising early results against the virus: The drug reduced combined hospitalizations and deaths by about 89% among high-risk adults when taken shortly after initial COVID-19 symptoms.

The FDA is expected to rule on whether to authorize Pfizer’s pill soon. 

RELATED: Pfizer: COVID-19 pill remains effective against severe disease, omicron variant

Flu

Oral antiviral medications can address symptoms and sometimes shorten the duration of the illness. Because they are given by mouth, these antiviral therapies can be prescribed for patients who are not hospitalized — as well as for those in the hospital.

"For the cold and the flu, typically it’s symptom management and I think for flu, we do have antivirals that can be prescribed by a PCP or a doctor. With COVID, we do have the monoclonal antibodies which could be given outpatient which is an IV infusion. So you do need to go to a clinic or some infusion center for that. When you are hospitalized there is an antiviral that we do give to people. So it depends on where you end up. The best advice that I can give somebody, if you do test positive and you are infected, seek medical help and maybe within the first couple of days of you being sick, you could receive the monoclonal antibody which would then prevent you from getting hospitalized and getting severe disease," Flinn said.

Vaccines

Both COVID-19 and the flu have vaccines to prevent illness whereas the common cold is more so about following regular preventative health measures, such as isolating if sick and practicing general good hygiene.

Moderna, Pfizer and BioNTech and Johnson & Johnson all have COVID-19 vaccines approved by the FDA and most health care facilities and pharmacies provide the seasonal flu shot every year. 

However, if someone becomes infected with a cold and they are scheduled to get either a COVID-19 vaccine or flu shot, Flinn advises to wait until any symptoms subside before getting the jab. 

"When is that incubation period? Where are you in your timeline of fighting off that infection? With the mRNA vaccine, what’s happening is it’s telling your body what proteins to look out for and then creating antibodies against it. So you are going to have an immune response. So if you’re fighting off an infection plus trying to create antibodies against another, you not feel really well. So I would wait a little bit. Get over what you have right now and then get vaccinated. Those that were infected with COVID-19, typically we have them wait a little bit before giving them that vaccine," Flinn said.

Flinn advises waiting at least three weeks before getting the COVID-19 vaccine after being sick from a cold, the flu or even COVID-19. 

RELATED: Fauci: Americans may 'just have to deal with' more COVID boosters

Get tested

While Googling whether or not you have COVID-19 or a common cold is potentially an easier solution to self-diagnose yourself, the best and strongest advice Flinn wants to leave with people is simple — get tested by a health care professional.

"My rule of thumb is — get tested," Flinn said. "If you don’t know if it’s the flu, if it’s COVID, if it’s allergies, if it’s RSV, whatever is circulating at that time, getting tested is the best way to know what you’re dealing with and you can plan accordingly." 

Kelly Hayes contributed to this report.