Flu or influenza is a virus infection caused by influenza viruses. It is extremely contagious, infecting the upper respiratory tract (nose and throat) and sometimes lower respiratory tract (bronchi and lungs). It causes mild to severe illness. The best way to prevent flu is to take flu vaccine once every year.

What are the symptoms of flu?

Flu is different from a common cold. A person who has flu might have some of the following symptoms:

  • Fever or feeling feverish
  • Cough
  • Sore throat
  • Running or stuffy nose
  • Fatigue/muscle ache
  • Body pain
  • Sometimes Diarrhoea in case of children
  • Some people with flu may not have fever/feel feverish

Cold climate is conducive for the growth of flu virus/flu activity.

FAQ About Flu

Who can get Flu?

Anybody can get flu but children below 8 years of age and health care professionals (doctors, nurses, ICU staff and phlebotomists) are at a higher risk of getting flu. Following are at more risk of developing complications with flu:

  • Children below 8 years of age
  • Pregnant women
  • Elderly people above 65 years of age
  • People with chronic illnesses e.g. diabetes, bronchial asthma and ischemic heart diseases

Normally flu does not cause complications if treated well, only few people might get serious illness.

Who should take flu vaccine?

Ideally everybody should take flu vaccine yearly.

Which flu vaccine to take?

Two varieties of flu vaccines are available:

  • Trivalent vaccine contains inactivated virus for two strains of influenza A (H1N1 and H3N2) and one strain of influenza B
  • Quadrivalent vaccine contains two strains of influenza A (H1N1 and H3N2) and two strain of influenza B

One should take whatever is available, obviously quadrivalent is better.

WHO Recommendations on Flu/Flu Vaccine

Every year WHO declares constitution of flu vaccines depending on circulating viruses in northern and southern hemispheres.

In northern hemisphere the flu season starts from October till March. In southern hemisphere flu season starts from April till August.

In tropical and sub-tropical areas of the world (northern and southern hemispheres) there are multiple peaks of flu activity and year-round identifiable flu cases. So these countries face two challenging questions:

  • When to vaccinate
  • Which formulation type (northern or southern hemisphere – NH/SH)to use

WHO Global Influenza Program recommends an evidence based practical approach to group countries, which share similar seasonality patterns and virus antigenic characters, into influenza vaccination zones to address country needs.

Influenza Vaccination Zones and Vaccination Formulations (northern or southern hemisphere type – NH/SH)

Vaccination Timings

WHO recommends that for northern hemisphere vaccination should start in October and for southern hemisphere vaccination should start in April.

For tropics and sub-tropics, with multiple peaks and year round flu activity, WHO recommends seasonal influenza vaccine before the start of primary period of flu activity. WHO recommends that countries should have strong surveillance system to assess their seasonality pattern at national and sub-national level and take evidence based decision on timing of vaccination campaigns.

Flu Activity in India

Flu season in India starts with the onset of monsoon in June/July. Climate becomes cold which is conducive for the growth of flu virus. This activity continues till September end/October beginning.

Timeframe for vaccination should start in June every year. As per WHO, India comes in SH zone, so we normally get vaccines available for Southern Hemisphere – hence we should use them.

With the onset of winter in November, the flu virus becomes active again in northern states of India including Jammu and Kashmir, so flu vaccination can be done during that timezone (November) for those who have not been vaccinated in June. In November month, we can use any vaccine (NH/SH) depending on whatever is available at that time.