CME INDIA Presentation by Dr. S. K. Gupta, MD (Med), FICP, CFM (France) Clinical Asst. Professor GS Medical College, CCSU, Uttar Pradesh, India. Visiting Consultant, Max Super Specialty Hospital, New Delhi. (With inputs from Dr. Arjun Khanna, Senior Pulmonologist, Delhi).

This season again baffles physicians. Cases with Flu like symptoms are visiting OPDs. There is a thin line to differentiate it with many other similar diseases and no wonder sometimes we miss COVID-19, thinking it as Flu.

For influenza, there is an old saying that if you find a remedy for it, it lasts for a couple of days. If you don’t, it still lasts for a couple of days. But for COVID 19, this policy can be dangerous.

Is it Influenza or COVID-19? Fever season soars

Many cases of Viral Sore Throat with fever Seasonal Flu (influenza) in Delhi and many parts of India  are soaring.

Symptoms include

  • Fever, Chills
  • Cough(Dry), Sore throat
  • Fatigue/ Weakness
  • Body aches.

Children, pregnant women and the elderly are at risk from severe infection.

Investigation in uncomplicated cases:

  • Normal cell counts in CBC
  • Normal enzymes in LFT and
  • Normal KFT
  • As usual Typhi dot or Widal may be falsely positive due to anamnestic response
  • X-ray Chest is Normal

Investigation of Choice

  • One may Order a throat swab for H1N1

How to differentiate Influenza from Covid

  • Uncomplicated influenza cases maintain good SpO2~ 98 to 99%.
  • In case of Low SpO2 get suspicious of Covid (especially in absence of underlying copd/ILD or heart disease).
  • Advise Covid RT PCR in cases of high suspicion.
  • Luckily Covid Positivity Rate in Delhi is very low these days. (July 21)

Treatment of Flu

  • Basic supportive care
  • Hydration
  • Analgesics
  • Cough suppressants
  • Antihistaminic
  • Oseltamivir (Tamiflu) – can be used in cases of high Suspicion of H1N1 especially in elderly population:
  • Effective if used early in course of disease even prior to onset of fever.
  • Empiric antiviral treatment should be considered for confirmed, probable, or suspected cases of H1N1 influenza.

Influenza A

  • Prophylaxis as well as treatment (Off label)
  • (Tamiflu)
  • 75 mg PO per Day for 7-10 days
  • Initiate within 48 hours of exposure


Vaccination for Influenza

  • Influenza is a rapidly mutating virus.
  • Sensitize all patients for annual influenza vaccine single shot in September.
  • Vaccine is available as:
  • Fluquadri® Adult MRP Rs 1690.
  • Flurix Tetra® MRP Rs 1900.

Who needs Influenza Vaccine?

  • Vaccination (Annual) should be advised to all adults esp. more than 55 years who are at risk of severe disease.
  • Even to those who have suffered from disease/infection may need annual vaccination because new strains tide over the immunity.
  • Influenzas vaccines are tweaked every year depending upon prevalent strain
  • So, use latest vaccine not the old stock.
  • Children and Pregnant ladies are also need vaccination that too on priority.

Does HIB vaccine used in infants protect against Seasonal Influenza?

  • HIB vaccine is used in infants against protection from Haemophilus influenzae type b (Hib) infection which is a Gram-Negative Coccobacillus causing invasive disease in infants and young children like bacteraemia, pneumonia, epiglottitis and acute bacterial meningitis.
  • However, Seasonal Flu is caused by Influenza Virus so HIB vaccine doesn’t give any immunity against Virus.

Influenza (flu) and COVID-19 are both contagious respiratory illnesses, caused by different viruses – Corona and Influenza Virus.

Currently COVID-19 seems to spread more easily than flu.
COVID-19 can cause more serious illnesses in some people.
Thrombosis not seen in Flu.
COVID-19 can also take longer before people show symptoms (Covid 2 to 14 days, typically 5 days) and 1 to 4 days in Flu.
People can be contagious for longer (Covid 2 day prior to till 10days after the onset of symptoms).
Influenza remains contagious from 1 day prior to onset of symptoms till 4 to 5 days after but not more than 7 days.

Can Flu and Covid be differentiated clinically?

  • No. Because some of the symptoms of flu and COVID-19 are similar, the difference between them cannot be made based on symptoms alone.
  • Testing is needed to confirm a diagnosis.

Can Flu and Covid occur at same time?

  • Yes. People can be infected with both flu and COVID-19 at the same time and have symptoms of both influenza and COVID-19.

Flu is Very common

More than 10 million cases per year (India)

  • Spreads easily
  • Partly preventable by vaccine
  • Usually, self-treatable
  • Usually, self-diagnosable
  • Lab tests or imaging rarely required
  • Short-term: resolves within days to weeks

How flu spreads?

  • By airborne respiratory droplets (coughs or sneezes).
  • By touching a contaminated surface (blanket or doorknob).
  • By saliva (kissing or shared drinks).
  • By skin-to-skin contact (handshakes or hugs).

Which Receptors:

  • Virus locks on to Siliac Acid Receptors present on Respiratory Epithelium

Diagnostic test for Influenza virus

  • Sample is respiratory secretions such as throat, nose, and nasopharyngeal secretions. (throat swab).
  • A rapid influenza diagnostic test (RIDT) tells whether a person has H1N1 infection by detecting influenza viral nucleoprotein antigen.
  • Commercially available RIDTs can provide results within 30 minutes.
  • Specificity of Rapid tests varies from 51% to 11%.
  • H1N1 RTPCR is confirmatory test for Virus but required in severe cases only for confirmation.

Subtypes Influenza A&B

  • Influenza virus has Haemagglutinin H and Neuraminidase N Receptors on surface and various combinations of H&N are termed as various subtypes. H1N1 is one such subtype.

Difference between Influenza A and B

  • Influenza B almost exclusively infects humans and is less common than influenza A.
  • A type also affects various animals like pigs, birds, whales and jumps over to humans
  • A type Mutates faster
  • Responsible for Pandemics
  • Flu type B
  • Also mutates about two to three times more a year but more slowly than influenza A.
  • Because humans are the natural host of influenza B, pandemics generally do not occur with influenza B viruses.

Covid, Common Cold and Flu?

Is It Influenza Or COVID-19? Fever Season Soars

  • Covid Flu and the common cold all are respiratory illnesses but they are caused by different viruses. Because these illnesses have similar symptoms, it can be difficult to tell the difference between them based on symptoms alone.
  • In general, flu is worse than the common cold, and Systemic symptoms are more intense.
  • Colds are usually milder than flu.
  • People with colds are more likely to have a runny or stuffy nose.
  • Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations.
  • Flu can have very serious complications more so in Covid.

Causes of the Common Cold

  • Rhinoviruses are the most common cause of Common cold  (More than 50%) Virus lives best at 31℃ which is the temperature inside nose
  • Common cold attack usually occurs at beginning of winter.
  • Other viruses that can cause colds include:
    • Respiratory syncytial virus, 
    • Human parainfluenza viruses, 
    • Adenovirus, 
    • Common human coronaviruses, and
    • Human metapneumovirus.
  • Rhinoviruses  can also trigger asthma attacks and have been linked to sinus and ear infections.

Learning PointsInfluenza (Flu) Versus Covid

1️. Contagious: Spread of infection

Before Symptoms

  • Both COVID-19 and flu, can spread the virus for at least 1 day before appearance of symptoms.

After onset of Symptoms:

  • Flu
    • Older children and adults with flu appear to be most contagious during the initial 3-4 days of their illness. Many people with Flu remain contagious for about 7 days.
  • COVID-19:
    • Contagious for 10 days or longer
    • Hospitalized with severe disease contagious for 20 days or longer.

2️. Modes of Spreads

  • Both COVID-19 and flu can spread from
  • Person-to-person on close contact(within~ 6 feet).
  • Spread mainly by large and small particles containing virus  expelled on cough, sneeze, or talk. These particles are inhaled and cause infection.
  • Contact of infected surface  by touching and then touching their own mouth, nose, or eyes.


  • COVID-19 is generally more contagious than flu viruses.
  • Super spreading events in Covid than flu.

3️. Who has High-Risk for Severe Illness?

Both COVID-19 and flu highest risk of Severe Disease include:

  • Older adults
  • People with certain underlying medical conditions (including infants and children)
  • Pregnant people


  • COVID-19 seems to cause more serious illness in some
  • Flu affects children while covid affects Elderly
  • For children younger than 5 years old, the risk of serious complications is higher for flu compared with COVID-19.

4️. Complications


  • Most people who get flu will recover on their own in a few days to two weeks.,
  • Some people have severe complications
  • Secondary bacterial infections are more common with influenza than with COVID-19.
  • Diarrhea is more common in young children with flu than in adults with flu.

Additional complications with COVID-19

  • Blood clots in the veins and arteries of the lungs, heart, legs or brain
  • Multisystem Inflammatory Syndrome in Children (MIS-C) and in Adults (MIS-A)
  • Long COVID can last weeks or months after first being infected with the virus that causes COVID-19
  • Long Covid can appear weeks after infection.
  • Long COVID can happen even after mild illness even in adults who had asymptomatic infection .

5️. Treatment

Supportive medical care to help relieve symptoms and complications.

Antiviral drugs to be used in Flu if

  • Hospitalized with flu or
  • At increased risk of complications and have flu symptoms

6️. Vaccine

  • Vaccines for COVID-19 authorized for emergency use (EUA).
  • Multiple FDA licensed influenza vaccines produced annually to protect against the 4 flu viruses that scientists expect will circulate each year.

CME INDIA Tail Piece

Basic information on QUADRIVALENT Inactivated Influenza vaccine (Split virion) I.P. NH 2020-2021 FluQuadri®

  • An inactivated quadrivalent influenza vaccine indicated for the prevention of influenza disease caused by influenza types A and B viruses contained in the vaccine.
  • It is approved for use in persons 6 months of age and older.
  • For intramuscular use only Dose.

Dose and Schedule for FluQuadri:

  • 1 or 2 doses depends on vaccination history as per Advisory Committee on Immunization Practices annual recommendations on prevention and control of influenza with vaccines
Is it Influenza or COVID-19? Fever season soars
  • The preferred sites for intramuscular injection are the anterolateral aspect of the thigh in infants 6 months through 11 months of age, the anterolateral aspect of the thigh (or the deltoid muscle if muscle mass is adequate) in persons 12 months through 35 months of age, or the deltoid muscle in persons ≥36 months of age the vaccine should not be injected into the gluteal area or areas where there may be a major nerve trunk.

FluQuadri® Ingredients

Is it Influenza or COVID-19? Fever season soars
  • Antibodies against one influenza virus type or subtype confer limited or no protection against another. Furthermore, antibodies to one antigenic variant of influenza virus might not protect against a new antigenic variant of the same type or subtype.
  • Frequent development of antigenic variants through antigenic drift is the virologic basis for seasonal epidemics and the reason for the usual change of one or more new strains in each year’s influenza vaccine. Therefore, influenza vaccines are standardized to contain the hemagglutinins of influenza virus strains representing the influenza viruses likely to be circulating in the next season.
  • Annual vaccination with the current vaccine is recommended because immunity during the year after vaccination declines and because circulating strains of influenza virus change from year to year.

COVID Vaccination and Influenza vaccine

  • CDC – Unless urgent vaccination is recommended, routine vaccinations should be given either 14 days before or 14 days after receipt of a COVID-19 vaccine.

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