Context
The Indian Council of Medical Research (ICMR) has clarified that no new strain of Influenza A (H1N1) has been identified in India. The influenza viruses currently circulating are reportedly well matched with the strains covered by the seasonal influenza vaccine.
What is H1N1?
- H1N1 is a subtype of Influenza A virus.
- It is commonly associated with swine flu.
- The strain responsible for the 2009 influenza pandemic is known as A(H1N1)pdm09.
- Since then, A(H1N1)pdm09 has continued to circulate as a seasonal influenza virus.
What has ICMR said?
The currently circulating H1N1 viruses:
- Are similar to A/Missouri/11/2025 (H1N1)pdm09-like virus.
- Have been circulating since 2025.
- Are well matched with the vaccine strains recommended for the Northern Hemisphere.
Therefore, the rise in cases does not indicate the emergence of a novel H1N1 strain.
Types of Influenza Virus
| Type | Key Feature |
| Influenza A | Causes seasonal epidemics; classified into subtypes such as H1N1 and H3N2; capable of causing pandemics |
| Influenza B | Causes seasonal epidemics; classified into lineages |
| Influenza C | Usually causes mild respiratory illness |
| Influenza D | Primarily affects cattle; not known to cause illness in humans |
| Important CTC from this article for UPSC 1. H1N1 2. NCMR |
Q. With reference to Influenza viruses, consider the following statements:
1. Influenza A and Influenza B viruses can cause seasonal epidemics in humans.
2. Influenza A viruses are classified into subtypes such as H1N1 and H3N2.
3. Influenza D viruses are known to cause seasonal epidemics in humans.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a) 1 and 2 only
Explanation:
Statement 1 is correct: Influenza A and B viruses are responsible for seasonal influenza epidemics in humans.
Statement 2 is correct: Influenza A viruses are classified into subtypes based on two surface proteins—Haemagglutinin (H) and Neuraminidase (N). Hence, subtypes such as H1N1 and H3N2 occur.
Statement 3 is incorrect: Influenza D primarily affects cattle and other animals and is not known to cause seasonal epidemics in humans.