Flu and COVID-19 are both contagious respiratory diseases, but caused by different viruses. While more and more is being learned every day about COVID-19 and the virus that causes it, there are still aspects, such as post-COVID conditions, that are to date under study. Cold has differences in symptoms and general characteristics that are more pronounced than influenza and COVID-19, so we focus on the differences and similarities between these diseases.
Because some of the symptoms of influenza, COVID-19 and other respiratory diseases are similar, the difference between them cannot be made based on symptoms alone. The specific test is indeed necessary to confirm a diagnosis. However, people can be infected with both influenza and SARS-CoV-2 at the same time and have symptoms of both one and the other. An in-depth CDC review explains how although influenza and COVID-19 share many characteristics, there are some key differences between the two.
Covid-19 and Influenza: similarities and differences
What is the cause?
COVID-19: caused by SARS-CoV-2.
Influenza: caused by influenza virus. There are two main types of influenza viruses called influenza A and influenza B. Different strains of influenza A and influenza B emerge and circulate every year.
After how long, do symptoms appear?
.Similarities
Both for COVID-19 and influenza, one or more days may elapse between infection and the onset of symptom manifestation.
Differences
A person infected with SARS-CoV-2 may take longer to develop symptoms than a person with influenza.
In influenza generally a person develops symptoms 1 to 4 days after infection.
In COVID-19, a person generally develops symptoms 3 to 5 days after infection, although evidence has shown that they can appear as early as 2 days after or as late as 14 days after infection.
What are the symptoms?
Similarities
Both COVID-19 and influenza can present with varying levels of signs and symptoms, ranging from no symptoms (asymptomatic), paucisymptomatic (illness that presents mild symptoms that can be mistaken for a simple passing malaise) to severe symptoms. Common symptoms that COVID-19 and influenza share include:
- Fever or feeling feverish/chills
- Cough
- Shortage of breath or difficulty breathing
- Fatigue (tiredness)
- Inflamed throat
- Running or stuffy nose
- Joint or muscle pain
- Headache
- Vomiting and diarrhea, especially in children
- Change or loss of taste or sense of smell, although this is more common with COVID-19.
Differences
The Guardian in the article "Coronavirus symptoms: how to tell if you have a common cold, flu or Covid" elaborates on the topic by specifying that the most common symptoms of COVID-19 are a fever-usually with a temperature greater than 37.8°C-a persistent cough (usually dry) and a loss of the sense of taste and/or smell. Patients may also sometimes suffer from fatigue, pain, sore throat, headache and shortness of breath. Diarrhea and nasal congestion are rare.
In the common cold, on the other hand, the most common symptoms are sneezing, pain, nasal congestion, and sore throat. You may experience a mild cough, fatigue but it is rare to have fever or headache. Colds do not cause diarrhea.
Finally, influenza is most commonly manifested by fever, fatigue, dry cough, aches, and headache. Patients will sometimes experience nasal congestion or sore throat. Sometimes diarrhea may occur in children. Sneezing or shortness of breath generally do not occur.
How long can someone spread the virus?
.Similarities
Both for COVID-19 and influenza, it is possible to spread the virus from at least 1 day before manifesting any symptoms.
Differences
A person with COVID-19, may be infectious for a longer period of time than someone with influenza.
How long are you contagious with the flu: Most people with the flu are contagious for about 1 day before they experience symptoms. Adults with influenza seem to be most contagious during the first 3-4 days of their illness, but many people remain contagious for up to 7 days. Infants and people with weakened immune systems may be contagious even longer.
How long one is contagious with SARS-CoV-2: How long someone can spread SARS-CoV-2 is still under investigation. It is possible for people to spread the virus for about 2 days before they show signs or symptoms and remain contagious for at least 7 days after onset. If someone is asymptomatic or their symptoms disappear, it is possible to remain contagious even for 10 days after testing positive for COVID-19. People hospitalized with serious illness and people with weakened immune systems can be contagious for 20 days or more.
How do they spread?
.Similarities
Both COVID-19 and influenza can spread between people who are in close contact with each other. Both are spread mainly by viral particles that are expelled when people with the disease (COVID-19 or influenza) cough, sneeze or talk. These particles can be inhaled by people in the vicinity.
Although most of the spread occurs by inhalation, it is possible for a person to be infected by, for example, shaking hands with someone who has contaminated hands, or by touching a contaminated surface or object, and then touching their mouth, nose or eyes.
People infected with coronavirus or influenza may not realize they are sick for several days, and during this time they may unknowingly spread the disease to others even before they develop symptoms.
Differences
While the virus that SARS-CoV-2 and influenza viruses are thought to spread in similar ways, the virus that causes COVID-19 is generally more contagious than influenza viruses. In addition, it has been observed that SARS-CoV-2 has more superspread events than influenza. This means that it can spread quickly and easily to many people and cause continuous spread among people as time passes.
Risk of serious illness?
.Similarities
Both COVID-19 and influenza disease can cause serious illness and complications.
Those at highest risk include:
- The elderly
- People with comorbidities
- Pregnant women
Differences
All in all, COVID-19 seems to cause more severe disease in some people.
Serious illness from COVID-19 leading to hospitalization and death can in fact occur even in healthy people. Rarer occurrence in influenza case.
Complications
Similarities
Both COVID-19 and influenza can cause complications, including:
- Pneumonia
- Respiratory failure
- Acute respiratory distress syndrome (fluid in the lungs)
- Sepsis (a life-threatening illness caused by the body's extreme response to an infection)
- Cardiac damage (e.g., heart attacks and strokes)
- Multi-organ failure (respiratory failure, renal failure, shock)
- Worsening of chronic medical conditions (involving the lungs, heart or nervous system, or diabetes)
- Inflammation of the heart, brain, or muscle tissues
- Secondary infections (bacterial or fungal infections that may occur in people who have already been infected with influenza or COVID-19)
Differences
Flu: Most people who contract the flu will recover on their own in a few days to two weeks, but some people will experience serious complications, requiring hospitalization. Secondary bacterial infections are more common with influenza than with COVID-19.
Diarrhea is more common in children with influenza.
Additional complications associated with COVID-19 may include:
- Blood clots
- Multi-systemic inflammatory syndrome in children (MIS-C) and adults (MIS-A)
The long-COVID is a condition characterized by a range of symptoms that may last weeks or months after first being infected with SARS-CoV-2 or may appear weeks after infection. long-COVID can occur in anyone who had COVID-19, even if their illness was mild or they had no symptoms.
Prevention
In most cases, serious illness and death due to COVID-19 or influenza can be prevented by vaccines. In addition, wearing a face mask, washing hands frequently and thoroughly, coughing in the crook of the elbow, staying home when sick, and limiting contact with infected people are effective safety measures, just as physical distancing limits the spread of COVID-19 and influenza in communities.
Vaccination
COVID-19: The following vaccines are currently licensed in Italy:
- Pfizer-BioNtech's Comirnaty vaccine - it is the first vaccine to be licensed in the European Union: on December 21, 2020 by the European Medicines Agency (EMA) and on December 22 by the Italian Medicines Agency (AIFA).
- Spikevax vaccine (Modern) - was authorized on January 6 by the EMA and on January 7 by AIFA.
- AstraZeneca's Vaxzevria vaccine - on January 29 it was cleared by the EMA and on January 30 by AIFA.
- Janssen (Johnson & Johnson) vaccine - it is the fourth vaccine licensed by the EMA on March 11 and by AIFA on March 12, 2021.
Flu: A vaccine is available that is safe and effective in preventing infection and reducing the severity or duration of influenza. The flu vaccine is reformulated every year in anticipation of the flu strains that are expected to circulate. Therefore, it is very important to receive the flu vaccine every year.
Global cases
.COVID-19: The first cases appeared in China in late 2019. Currently, (as of September 30, 2021) there are 233,136,147 confirmed cases worldwide since the start of the pandemic, including 4,771,408 deaths (Health Emergency Dashboard). In Italy, confirmed cases have reached 4,660,314 and 130,697 deaths.
Flu: The World Health Organization estimates that the influenza virus affects between 5 and 15 percent of the adult population (i.e., 350 million to 1 billion people). Estimates alarm that death is needed in about 250-500 thousand people, especially among fragile population groups such as the elderly and people with chronic diseases. (EpiCenter)
The flu season in the COVID-19: what should I do?
- Consult your doctor and get the COVID-19 vaccine; .
- Consult your doctor and get the flu vaccine or contact us to get it at one of our vaccination centers.
Take care of yourself and your family with good nutrition, plenty of rest, proper hydration, regular exercise and stress management. Stay home if you don't feel well.
Even if you feel tired of following precautions, such as washing your hands often, cleaning and sanitizing, wearing a face mask, and maintaining physical distances, it is especially important now, especially with the onset of the fall-winter season, to continue to observe all preventive measures and encourage others to do the same.
Where to test for Covid-19
If you have symptoms, contact your primary care physician to report the situation and ask what procedure to follow.
If you need to book a swab or serologic test, privately, even if only to be on the safe side, you can book it privately and/or get information about it, by going to the following link: COVID-19 TESTING RESERVATION.
These services are carried out at Ambimed's partner collection points locatedall over Italy.
Find out more about influenza in our section dedicated to diseases and vaccinations.
In the table below we have compared the main symptoms between Covid-19, colds and flu. Find out the differences but be very careful! The table has informative value only, not scientific. If you have any doubts, it is important to consult your doctor.
Sources:
CDC, Johns Hopkins
