LEARNING OUTCOME AND OBJECTIVES:  Upon completion of this course, you will be prepared to differentiate between COVID-19 and seasonal flu and discuss both treatment and vaccination for these two conditions. Specific learning objectives to address potential knowledge gaps include:

• Differentiate between the clinical presentation of COVID-19 and seasonal flu.
• Explain the incubation, period of contagion, transmission, and possible long-term effects of the COVID-19 and influenza viruses.
• Discuss infection prevention measures for influenza and COVID-19.
• Describe patient education considerations for influenza and COVID-19.
• Explain treatment and vaccination guidelines for seasonal flu and COVID-19.

DIFFERENTIATING BETWEEN INFLUENZA AND COVID-19

Countries throughout the world are grappling with the effects of COVID-19, which is the worst pandemic since the Spanish Flu Pandemic in 1918–1919. While there is still a great deal not known about COVID-19 and the SARS-CoV-2 virus that causes it, some valuable information is available to guide healthcare professionals.

Concerns about COVID-19 in the context of the annual influenza (flu) season also raise questions for healthcare professionals, such as:

• How is the flu related to COVID-19?
• How can I tell the difference between the flu and COVID-19?
• What are the symptoms of COVID-19, and how long does it take for them to appear?
• How long is someone contagious after developing COVID-19 or the flu?
• How are COVID-19 and the flu transmitted?
• What steps can be taken to prevent COVID-19 and flu infection?
• What do I need to teach patients and families about COVID-19 and the flu?
• Should people get a flu shot during the pandemic?
• How can vaccines be safely administered during the pandemic?

Signs and Symptoms of COVID-19 and Influenza

Some symptoms overlap between COVID-19 and influenza. It is important to know the clinical manifestations of each condition and how to differentiate between them.

Both the flu and COVID-19 are contagious respiratory illnesses, but they are caused by different viruses. COVID-19 is caused by infection with the coronavirus SARS-CoV-2, and the flu is caused by infection with a variety of influenza viruses. More recent strains of SARS-CoV-2 are known to spread more easily than the flu.

Since influenza and COVID-19 share a number of symptoms, differentiation between the two can be problematic. Both the flu and COVID-19 can cause mild to severe illness, including these common signs/symptoms:

• Fever
• Chills
• Cough
• Shortness of breath or difficulty breathing
• Fatigue
• Sore throat
• Runny or stuffy nose
• Muscle pain
• Body aches
• Headache
• Vomiting and diarrhea (typically more common in children than in adults)
  (CDC, 2022a)

Loss of taste or smell is typically associated with COVID-19. Although such symptoms are more common with COVID-19, some patients with the flu may have alterations in taste and smell as well (CDC, 2021a; Mayo Clinic, 2022a).

Additional symptoms that are found in patients with COVID-19, but not typically in those with influenza, include red, swollen eyes and skin rashes (NYPMG, 2022).

Symptoms of COVID-19 can be mild at the beginning but become more intense over 5–7 days, with cough and shortness of breath becoming worse if pneumonia develops. The severity of illness can vary significantly from person to person. A person may have a cough or other symptoms but no fever (or a low-grade fever), particularly in the first few days of illness. It is also possible for a person infected by the SARS-CoV-2 virus to have minor or even no symptoms at all.

There is also evidence that COVID-19 vaccination may make illness less severe for those who are vaccinated and still become infected, known as “breakthrough infection” (see box below) (CDC, 2021a; Johns Hopkins Medicine, 2022).

COVID IN CHILDREN

Children of any age can get COVID-19 and experience its complications. Children are as likely to get COVID-19 as adults. However, they are less likely to become severely ill. Nearly 50% of children and adolescents with COVID-19 have no symptoms (Mayo Clinic, 2022b).

Risk factors for serious illness with COVID-19 in children include:

• Obesity
• Diabetes
• Asthma
• Congenital heart disease
• Genetic conditions
• Conditions affecting the nervous system or metabolism
• Babies who are less than 1 year old
  (Mayo Clinic, 2022b)

Children are at risk for a rare complication known as multisystem inflammatory syndrome in children (MIS-C), in which various body parts become inflamed, including the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal organs. Signs and symptoms of MIS-C include:

• Fever that lasts 24 hours or longer
• Vomiting
• Diarrhea
• Pain in the stomach
• Skin rash
• Fast heartbeat
• Rapid breathing
• Red eyes
• Redness or swelling of the lips and tongue
• Feeling unusually tired
• Redness or swelling of the hands or feet
• Headache, dizziness, or lightheadedness
• Enlarged lymph nodes

Emergency warning signs necessitating emergency care include the inability to breathe; inability to stay awake; new confusion; pale, gray, or blue-colored skin, lips, or nail beds; and severe stomach pain (Mayo Clinic, 2022b).

Incubation Period

One or more days can pass between becoming infected and when symptoms start to appear in both the flu and COVID-19. With influenza, patients typically develop symptoms within 1–4 days. Severe symptoms of the flu may develop and end quite swiftly, usually within 5 days.

The typical time frame for symptom development with COVID-19 is within 2–14 days after infection (CDC, 2022d). Research suggests that the median time for symptoms to appear from the omicron variant of COVID-19 is about 3 days. COVID-19 symptoms may develop more gradually, and severe symptoms may not appear for several days after exposure. During the recovery process, people with COVID-19 might have recurring symptoms alternating with periods of feeling better that persists for days or even weeks (Maragakis, 2022).

Degree of Communicability

It is possible to spread the flu and COVID-19 for at least 1 day prior to experiencing any symptoms.

With influenza, the majority of people are contagious for about 1 day prior to showing symptoms. It appears that older children and adults are most contagious during the initial 3–4 days of their illness, but many remain contagious for about 7 days. Infants and people with weakened immune systems may be contagious for an even longer period of time.

The onset and duration of viral shedding and the period of infectiousness for COVID-19 are not yet known with certainty. Research thus far indicates that on average, people can begin spreading the virus 2–3 three days before their symptoms begin, but infectiousness peaks 1 day before the beginning of symptoms (CDC, 2022d).

Emerging evidence suggests that persons who are vaccinated against COVID-19 but develop breakthrough infections are less likely to spread the virus because they shed it for shorter periods of time. However, the extent of this difference in contagion is unknown at this time (Rura, 2021).

Communicability and the Omicron Variant

Viruses constantly change via mutation, which can result in a new variant of the virus. Some variants emerge and disappear, while others persist (Mayo Clinic, 2022c). People who are up to date on COVID-19 vaccines, including booster doses when eligible, are likely to have stronger protection against COVID-19 variants, including omicron, which became the most prevalent variant in 2022 (CDC, 2022e).

The omicron variant has been designated by the CDC and other public health organizations as a variant of concern (VOC). A VOC is one for which there is evidence of an increase in transmissibility; more severe disease (for example, increased hospitalizations or deaths); significant reduction in neutralization by antibodies generated during previous infection or vaccination; reduced effectiveness of treatments or vaccines; or diagnostic detection failures (CDC, 2022f).

Characteristics of the omicron variant include:

• Spreads more easily than the original virus that caused COVID-19 and the later delta variant
• Causes less severe disease
• Shows similar symptoms to previous variants
• Presence and severity of symptoms affected by vaccination status, presence of other health conditions, age, and history of prior infection

Current COVID-19 vaccines protect against severe disease, hospitalizations, and deaths due to omicron infection. Breakthrough infections may still occur.

Scientists are also investigating the effectiveness of current treatments. Some monoclonal antibody treatments are less effective against omicron’s BA.2 lineage but continues to be effective against BA.1 and BA1.1 lineages. Other nonmonoclonal antibody treatments remain effective against omicron (CDC, 2022g).

Modes of Transmission

Both influenza viruses and SARS-CoV-2 can spread from person to person between people who are in close contact with each other (within about six feet). Research indicates that in some types of situations, such as indoor settings with poor ventilation, small droplets may be spread farther than six feet.

Both viruses are spread primarily by droplets (large and small) made when people who are infected cough, sneeze, or talk. These droplets can enter the mouths or noses of other people and be inhaled into the lungs.

It may also be possible to acquire infection by physical contact with infected people (e.g., shaking hands) or by touching contaminated surfaces and then touching the mouth, nose, or, possibly, the eyes (CDC, 2022a).

Although the COVID-19 virus appears to spread mainly by droplets, it can occasionally spread via finer aerosols that remain suspended in the air. The largest droplets containing SARS-CoV-2 settle out of the air rapidly, within seconds to minutes. The smallest very fine droplets, and aerosol particles formed when these fine droplets rapidly dry, are small enough that they can remain suspended in the air for minutes to hours (CDC, 2021a). This enables one person to infect many others, and large transmission clusters seem to be associated with aerosol transmission.

Infectious exposure to COVID-19 occurs in three main ways, and these are not mutually exclusive:

• Inhalation: Small droplets and aerosol particles that contain the virus travel through the air and reach susceptible people.
• Deposition: The virus is transported in droplets and particles onto exposed mucous membranes.
• Touching: Hands that are soiled with contaminated fluids touch mucous membranes, or hands touch inanimate surfaces contaminated with the virus.
  (CDC, 2021a)

Even though SARS-CoV-2 and flu viruses are believed to spread in similar ways, COVID-19 has been observed to have more “superspreading” events than the flu. This means the virus that causes COVID-19 can quickly and easily spread to many people, resulting in continuous spread as time progresses (CDC, 2022a). There are no exact criteria for superspreader events. There may be large gatherings where very few, or none, contract the virus. On the other hand, a small gathering may spread the virus to all attendees. The general definition of a superspreader event is one in which there is a greater amount of transmission than would be expected (Cleveland Clinic, 2020).

Complications

Although most people with COVID-19 have mild to moderate symptoms, the disease can cause the following complications:

• Pneumonia
• Respiratory distress
• Organ failure
• Cardiac problems and heart failure
• Acute respiratory distress syndrome
• Blood clots
• Acute kidney injury
• Additional viral and bacterial infections
  (Mayo Clinic, 2022d)

Most people who get the flu recover in a few days to less than two weeks. However, some people develop severe complications, such as:

• Pneumonia
• Bronchitis
• Asthma exacerbations
• Sinus and ear infections
• Acute respiratory distress syndrome
• Myocarditis
• Encephalitis
• Muscle inflammation
• Multiorgan failure
• Extreme bodily inflammatory response
• Sepsis
• Worsening chronic heart disease
  (CDC, 2021b)

POST-COVID CONDITIONS (LONG COVID)

Most people infected with COVID-19 recover within a few days to a few weeks. Thus, the start of post-COVID conditions is said to begin at least four weeks after infection. Post-COVID conditions are also referred to by various terms: long COVID, long-haul COVID, post-acute COVID-19, post-acute sequelae of SARS-CoV-2 infection (PASC), long-term effects of COVID, and chronic COVID.

Anyone who has been infected with COVID-19, even people with mild symptoms or no symptoms, can develop post-COVID conditions. Unvaccinated people may be at higher risk of developing post-COVID conditions compared to those who were vaccinated and had breakthrough infections. Additional higher-risk groups include those who experienced more severe symptoms, people who had an underlying health condition prior to COVID-19, and people who experience multisystem inflammatory syndrome (MIS) during or after COVID-19 illness (CDC, 2022i).

High-Risk Populations

AGE FACTORS

Older adults are more likely to develop serious illness from COVID-19 compared to younger adults. The risk increases for people in their 50s and increases further in the 60s, 70s, and 80s. The people who are most likely to get severely ill are those 85 years of age and older (CDC, 2021c).

It has been recognized for many years that people 65 years and older are also at high risk of developing serious complications from influenza when compared to young, healthy adults. In recent years, an estimated 70%–85% of seasonal flu–related deaths have occurred in people 65 years and older, and 50%–70% of seasonal flu–related hospitalizations have occurred among people in this age group (CDC, 2022j, 2022k).

Each year thousands of children are hospitalized and some children die from influenza. Children at higher flu risk include:

• Children younger than 6 months of age (who are too young to be vaccinated)
• Children ages 6 months to 5 years
• American Indian and Alaskan Native children
• Children ages 6 months to 18 years who have chronic health problems
  (CDC, 2021d)

HEALTH FACTORS

According to the CDC, many health conditions are known to increase a person’s risk of serious complications from both the flu and COVID-19 (see table below).

HEALTH FACTORS INCREASING RISK OF . . .

COVID-19	Influenza
(CDC, 2022l, 2021e)
Cancer Cardiac conditions Chronic renal disease Chronic hepatic disease Chronic respiratory disease Cystic fibrosis Dementia or other neurological conditions Diabetes, type 1 or type 2 Disabilities that interfere with performing activities of daily living HIV infection Immunocompromised condition or weakened immune system Mental health conditions Overweight and obesity Physical inactivity Pregnancy Sickle cell disease Smoking (currently or formerly) Solid organ or blood stem cell transplant Stroke or cerebrovascular disease Substance use disorders Tuberculosis Age 65 years and older	Age younger than 2 years Asthma Neurologic and neurodevelopment conditions Blood disorders (e.g., sickle cell disease) Chronic lung disease (e.g., COPD, cystic fibrosis) Endocrine disorders (e.g., diabetes) Heart disease (e.g., congenital heart disease, congestive heart failure, coronary artery disease) Kidney disease Liver disorders Metabolic disorders (e.g., inherited metabolic disorders, mitochondrial disorders) Obesity (BMI 40 or higher) People under age 19 years on long-term aspirin- or salicylate-containing medications Immunocompromised state due to disease (e.g., HIV/AIDS, some cancers such as leukemia) or medications (e.g., chemotherapy/radiation treatment for cancer, chronic corticosteroids, other drugs that suppress the immune system) Stroke Others at high risk: Pregnant women and women up to two weeks after end of pregnancy Nursing home and other long-term care facility residents Non-Hispanic Black persons, Hispanic or Latino persons, American Indian or Alaska Native persons