Both Covid-19 and influenza transmit primarily through the respiratory route
The recent reports of a rise in Covid-19 detections across the country comes on the heels of one of the largest influenza outbreaks in recent years. This year the influenza virus variant responsible for the flu was H3N2 and caused an increase in severity and prolongation of symptoms especially cough.
Covid-19 and influenza, both being transmitted primarily through the respiratory route, exhibit a commonality in symptoms, making a definitive clinical diagnosis difficult without a laboratory test for confirmation. However, clinical suspicion is the first step in guiding the diagnosis and understanding the symptoms and small differences in them is important.
Common signs and symptoms of Covid-19 and influenza
The overlap of symptoms between the two conditions is significant. Fever, chills, body aches, headache and fatigue are common. An itching in the throat leading to inflammation followed by a dry severe cough and a runny or stuffy nose is seen in flu and also with the currently prevailing Omicron variant of covid-19. Breathlessness can occur, especially in those with an existing respiratory condition like asthma. Cough is usually dry in nature and can get prolonged both in H3N2 and with long Covid-19. Other symptoms such as nausea, vomiting and diarrhea may manifest along with the respiratory symptoms.
Complications of both these conditions can be debilitating and lead to bronchitis, pneumonia and worsening of pre-existing medical conditions, leading to hospitalization and requirement of oxygen support.
How does one distinguish between the two?
There are however, several small differences between illness caused by influenza viruses (including H3N2) and covid-19 that can help clinicians towards a diagnosis:
- Covid-19 infections are more common in young adults and older individuals while influenza targets those below 8 years and above 65 years more
- The onset of symptoms of influenza occurs earlier after exposure (within 1-4 days) while Covid-19 takes longer to manifest (2-14 days). Based on the prevailing variant of either infection, this may change.
- The cough caused by H3N2 influenza is intense and persistent, leaving the affected individual exhausted. The cough in covid-19 is less severe and can persist only if the individual suffers from Long covid-19
- Influenza causes lower grade fever (between 99-101o F) than covid-19
- The feeling of fatigue is much more pronounced in covid-19 as compared to the flu
- Covid-19 leads to loss of smell or taste, on the other hand influenza does not do so
- Influenza also leads to gastrointestinal symptoms like diarrhea, nausea and vomiting
- Both illnesses can cause respiratory complications, but covid-19 is more likely to cause severe systemic illness and death, particularly in older adults and those with underlying medical conditions.
Preventing covid-19 and influenza:
Just as the symptoms of both infections are similar, prevention of infection is also based on common principles.
1. Awareness:
Creating awareness around the preventive aspects of respiratory infections is extremely important.
2. Vaccination:
Vaccination is the most effective way to prevent covid-19.
Flu vaccines change with the strains (variants) of the flu virus every year and hence, an annual vaccine is recommended for everyone above 6 months of age. This is usually a multi-strain vaccine and provides protection against H3N2 as well.
3. Hand hygiene:
Human touch their faces several times a day without even realizing it. Washing hands frequently with soap and water for at least 20 seconds is a simple yet effective way to prevent the spread of both viruses. Alternatively, using an alcohol-based hand sanitizer can also be helpful when soap and water are not available.
4. Masking:
Wearing a mask can reduce the spread of respiratory droplets that may contain either the influenza or covid-19 virus. A well-fitted mask, covering both the mouth and nose, protects both the wearer and those around them.
5. Social distancing:
Maintaining a physical distance of at least 2 meters or 6 feet from others can reduce the aerosolization of respiratory droplets that may contain the virus.
6. Cleaning and disinfecting:
Regularly cleaning and disinfecting surfaces, especially high-touch surfaces like doorknobs, light switches and countertops, can help to prevent the spread of the viruses.
7. Avoiding large gatherings:
Avoiding large gatherings, especially indoors, can help to reduce the spread of the viruses.
8. Quarantine and isolation:
If you have been exposed to covid-19 or H3N2, or if you have symptoms of the flu, staying home and isolating yourself can help to prevent the spread of the virus.
Prevention of these infections starts with a change in one's attitude and behaviour towards respiratory illnesses. Do not ignore the symptoms and follow all precautions to stay safe.
(Dr. Vikram Vora, Medical Director, Indian Sub-Continent, International SOS)
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