Seasonal influenza, commonly known as the flu, is a contagious viral respiratory disease. However, it is easily mistaken for the common cold – an infection caused by a different viral strain. Although there are many similarities between these infections, such as cough, sore throat and stuffy nose, there are some major differences. A person with the flu may also experience symptoms such as fever, cold sweats, body aches, headache, fatigue, vomiting and diarrhea, which do not occur for the common cold.
Let us take a closer look at the influenza virus and its effects on the increasing flu burden. As per WHO, approximately 65,000 people worldwide are affected by seasonal-influenza-related respiratory illnesses every year. Thirty-six per cent of them are from low to middle-income group countries, including India. Aside from the hospitalization rates for children in India and the severity of influenza burden being recorded, there are no national estimates available on influenza-related mortality.
Being vigilant during the monsoon and winter seasons
In temperate regions, influenza epidemics occur in the winter, whereas in tropical regions, seasonal epidemics appear to occur throughout the year with irregular outbreaks.
Due to the diverse climate across India, there are vast variations in the impact of influenza from the northern to southern regions. In some parts of the country, particularly in the north, influenza circulation peaks during the winter, whereas in other parts, it peaks during the monsoons. Thus, there is a need for year-round preparedness and region-specific approaches for influenza prevention.
Controlling and preventing influenza
One of the primary reasons for annual outbreaks is that the influenza virus undergoes constant but fairly minor genetic mutations. This is called the “antigenic drift”, and it prevents people from developing lasting immunity. For example, a person who has caught the flu in the previous year will develop immunity to that particular viral strain, although they may not have immunity to the current year’s strain due to the slight change in or evolution of its genetic structure.
Seasonal influenza is most often caused by different strains of type A or B influenza viruses, both of which are responsible for annual epidemics, with a prevalence rate of 5–10% and 20–30% in adults and children each year, respectively.
Globally, since September 2020, influenza activity was mostly reported from countries located in the tropics and subtropics as well as some countries present in the temperate zone of the northern hemisphere. India was among the tropical Asian countries that reported the greatest detection of influenza.
The influenza vaccine, popularly known as the ‘flu shot’, is the first protective step against the virus. With changes in the major influenza strains year-on-year, it remains essential to take the latest influenza vaccine, comprising an updated composition to provide adequate and relevant immunity.