Seasonal flu has begun with the fear of the H3N2 Influenza Virus spreading rapidly among the populations. It is a subtype of the Influenza A virus characterized by its highly contagious behavior. Read here to learn more about the H3N2 virus.
Influenza sometimes referred to as “the flu,” is a contagious illness brought on by influenza viruses. Fever, runny nose, sore throat, headache, coughing, and exhaustion are among the symptoms, which can range in severity from moderate to severe.
Pneumonia may develop from influenza and may be brought on either by the virus itself or by a subsequent bacterial infection. Acute respiratory distress syndrome, meningitis, encephalitis, and the aggravation of pre-existing medical conditions including asthma and cardiovascular disease are further consequences of infection.
Influenza viruses, which cause the infectious disease known as flu, are of four different types: A, B, C, and D.
- Influenza B virus (IBV) and Influenza C virus (ICV) primarily infect humans.
- Influenza D virus (IDV) is found in cattle and pigs.
Influenza A is further classified into different subtypes and one of them is H3N2.
- Aquatic and wild birds are the major source of the influenza A virus.
- It can spread to mammals too, including pigs and humans.
- Occasionally, it is transmitted from wild to domestic birds, and this may cause severe disease, outbreaks, or human influenza pandemics.
Influenza A is an RNA virus. It is categorized into subtypes based on the type of two proteins on the surface of the viral envelope-
- H for hemagglutinin, a protein that causes red blood cells to agglutinate.
- N for neuraminidase, an enzyme that cleaves the glycosidic bonds of the monosaccharide sialic acid (previously called neuraminic acid).
Various hemagglutinin and neuraminidase proteins are encoded by multiple influenza viruses.
- For instance, the type 5 hemagglutinin (H) and type 1 neuraminidase (N) proteins of the H5N1 virus define an influenza A subtype.
- Theoretically, 198 distinct combinations of these proteins are feasible given that there are 11 different forms of neuraminidase and 18 different types of hemagglutinin.
H3N2 Influenza Virus
The influenza-causing virus subtype H3N2 (A/H3N2) is a subtype of influenza viruses.
- Both birds and mammals can contract H3N2 viruses.
- The virus has evolved into several strains in pigs, humans, and birds.
- Hospitalizations are higher in years where H3N2 is the prevalent strain.
This virus is extremely contagious and spreads through droplets released by an infected person when coughing, sneezing, or talking.
According to the International Health Regulations (IHR), a human infection caused by a novel influenza A virus subtype is an event that has the potential for high public health impact.
A novel influenza A virus is considered to have the potential to cause a pandemic if-
- the virus has demonstrated the capacity to infect and transmit efficiently among humans;
- differs from currently-circulating seasonal human influenza viruses such that the hemagglutinin (HA) gene (or protein) is not a mutated form of those, i.e. A/H1 or A/H3, circulating widely in the human population;
- the population has little to no immunity against it.
Human infections with variant viruses tend to result in mild clinical illness, although some cases have been hospitalized with more severe disease. Nevertheless, human infections with these viruses need to be monitored closely.
What are the symptoms of H3N2?
Its symptoms are similar to that of any other flu.
- They include cough, fever, body ache and headache, sore throat, a runny or stuffy nose, and extreme fatigue.
- Nausea, vomiting, and diarrhea have been seen in very few cases.
According to the Indian Medical Association (IMA), an infection caused by H3N2 generally lasts for five to seven days and the fever starts going away after three days. However, the coughing can persist for up to three weeks.
According to the IMA, this virus typically preys on those under the age of 15 or over the age of 50.
- Risk factors include being a child, having co-morbid illnesses including asthma, diabetes, heart disease, a weaker immune system, and neurological or neurodevelopmental disorders.
H3N2 vs Coronavirus
Covid-19 and H3N2 influenza are both caused by contagious viruses. They can spread through droplets and can also mutate significantly.
- Even though both these respiratory illnesses are highly transmissible, they both belong to a different family of viruses.
- While COVID-19 is caused by the SARs-CoV-2 virus, H3N2 is one of the Influenza A subtypes circulating in humans.
- Reportedly, the latter can lead to more cases of hospitalizations compared to other strains.
- The time between infection to illness for the SARs-CoV-2 virus is said to vary from person to person and therefore, can range from 2 to 14 days.
- For seasonal influenza, the incubation period may be much shorter than the incubation period for COVID. The time from infection to illness is about 1-4 days.
Vaccines for influenza
The basis for developing flu vaccines is forecasting which H1N1, H3N2, H1N2, and influenza B “mutants” will spread throughout the upcoming season.
- In advance of their yearly epidemics, separate vaccinations are created for the Northern and Southern Hemispheres.
- The seasonality of influenza is unclear in the tropics.
- H3N2 has tended to outpace H1N1, H1N2, and influenza B in prevalence during the previous 10 years.
Seasonal H3N2 flu is a strain of H3N2 that affects humans and differs somewhat from one of the strains that circulated during the previous flu season.
Intermittent outbreaks in East Asia and Southeast Asia give rise to seasonal influenza viruses, which spread before dying off.
WHO Global Influenza Surveillance network
In 1952, the WHO Global Influenza Surveillance Network was created.
- The network consists of 112 institutions in 83 countries that are recognized by WHO as WHO National Influenza Centers, as well as 4 WHO Collaborating Centers (WHO CCs) (NICs).
- These NICs gather samples within their nation, carry out viral isolation from the start, and characterize the antigenic in the early stages.
- Each year, they send newly isolated strains to WHO CCs for high-level antigenic and genetic research.
- The results of this study serve as the foundation for WHO recommendations on the components of the influenza vaccine for the Northern and Southern Hemispheres.
H3N2 influenza in India
Union Health Ministry is keeping a close watch on the Seasonal Influenza situation in various States/UTs through the Integrated Disease Surveillance Programme (IDSP) network on a real-time basis.
The Ministry is also tracking and keeping a close watch on morbidity and mortality due to the H3N2 subtype of Seasonal Influenza.
Young children and old age persons with co-morbidities are the most vulnerable groups in the context of seasonal influenza.
In India, integrated surveillance of Influenza-like Illness (ILI) and Severe Acute Respiratory Illness (SARI) for the detection of the human influenza virus and SARS-COV-2 virus is ongoing through a structured ILI/SARI surveillance network of 28 sites.
- The surveillance network is comprised of 27 DHR-ICMR’s Virus Research & Diagnostic Laboratories and the country’s National Influenza Centre (WHO-NIC) housed at ICMR-National Institute of Virology Pune, also a WHO Collaborating Centre for Global Influenza Surveillance & Response System (GISRS).
Seasonal influenza like the H3N2 virus is an acute respiratory infection caused by influenza viruses that circulate in all parts of the world, and the cases are seen to increase during certain months globally.
Every year, India witnesses two peaks of seasonal influenza: one from Jan to March and another in the post-monsoon season. The cases arising from seasonal influenza are expected to decline from March end. State surveillance officers are therefore fully geared to meet this public health challenge.
Due to the evolution of influenza viruses, WHO continues to stress the importance of global surveillance to detect virologic, epidemiologic, and clinical changes associated with circulating influenza viruses that may affect human (or animal) health with timely sharing of such viruses and related information for further characterization and risk assessment.
-Article written by Swathi Satish