Flu Symptoms to Watch Out For as Winter Illnesses Surge

As we slowly trudge through winter, respiratory illnesses like COVID-19 and the flu are surging across the country.

For the week ending January 4, 18.6 percent of influenza tests came back positive, with influenza A(H1N1)pdm09 and A(H3N2) the most predominant variants during this period, according to the U.S. Centers for Disease Control and Prevention (CDC).

"Nationally, emergency department visits are high for diagnosed influenza," the CDC said. "Five influenza-associated deaths occurring during the 2024-2025 season were reported this week for a total of 16 deaths this season."

A stock image shows a woman with the flu, along with viruses in the inset image. Flu symptoms can include fevers, coughs, headaches and body chills. ISTOCK / GETTY IMAGES PLUS

The flu, or influenza, is a contagious respiratory illness caused by viruses and primarily affects the nose, throat and lungs. It is spread via respiratory droplets, which are emitted when an infected person coughs, sneezes or talks.

What Are the Symptoms of Flu?

Symptoms usually come on suddenly, according to the CDC, and can include fevers above 100.4 degrees F, dry cough, sore throat, runny nose, body aches, headaches, chills and occasionally nausea, vomiting or diarrhea.

Symptoms may be more severe for people over 65 or younger than 5, pregnant women and those with certain chronic medical conditions, such as asthma, diabetes or heart disease.

"Some people will develop complications (such as pneumonia) as a result of flu, some of which can be life-threatening and result in death," the CDC said. "Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle tissues (myositis, rhabdomyolysis), and multi-organ failure (for example, respiratory and kidney failure)."

COVID-19 symptoms and flu symptoms are very similar, insofar as they cannot be diagnosed by symptoms alone, with testing required to distinguish one from the other.

"Compared with flu, COVID-19 can cause more severe illness in some people. Compared to people infected with influenza virus, people infected with SARS-CoV-2 may take longer to show symptoms and may be contagious for longer periods of time," the CDC said.

Can You Have the Flu Without a Fever?

While fever is a common symptom of the flu, not everyone with the virus will develop one. If the infection is mild, the body might not generate a fever, but people with weakened immune systems or older people may not experience fever because of their lessened immune response.

How Long Does It Take to Recover From the Flu?

Recovery from the flu typically takes one to two weeks, but the timeline can vary depending on factors like age, overall health and the severity of the infection. Children and older adults may take longer to recover, and conditions like asthma, diabetes or heart disease can prolong recovery.

What Is the Difference Between Flu A and B?

Influenza A and B are two types of influenza viruses that cause seasonal flu outbreaks. Flu A is found in humans, birds, pigs and other animals, and its subtypes are based on its surface proteins: hemagglutinin (H) and neuraminidase (N) (for example, H1N1, H3N2).

Flu B, on the other hand, is found only in humans (and occasionally in seals). Flu A is more widespread and often the dominant strain during flu season. Flu B generally causes milder illness compared with flu A, but severe cases can still occur.

"Of the 1,783 viruses reported by public health laboratories, 1,743 were influenza A and 40 were influenza B," the CDC said.

Is It Too Late to Get a Flu Shot?

The flu season runs between October and May in most regions, peaking between December and February. While getting vaccinated earlier is ideal for maximum protection, getting the vaccine later can still be beneficial, especially if flu activity is ongoing in your area.

The vaccine takes approximately two weeks to reach full immunity, so getting it now can still protect you during the active part of the flu season. Even if you're exposed to the flu virus before full immunity develops, the vaccine can reduce the severity of illness and lower the risk of complications like pneumonia or hospitalization.

"CDC recommends that everyone ages 6 months and older get an annual influenza (flu) vaccine," the CDC said.

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