Influenza virus vaccine, H1N1 is used to prevent infection caused by the influenza A (H1N1) 2009 virus. The vaccine works by causing your body to produce its own protection (antibodies) against the disease. It is also known as a "flu shot".

The 1918 deadly influenza pandemic caused by H1N1 influenza virus, infected approximately 500 million people around the world and caused the death of roughly fifty to a hundred million people. The H1N1 variant of swine flu is the progeny of the strain that caused the 1918 swine flu pandemic.

The phylogenetic studies of all eight RNA gene segments of influenza A viruses may indicate that the 1918 pandemic strain originated from a H1N1 swine virus, which itself might be derived from a H1N1 avian precursor, which was separated from the bulk of other avian viruses in toto a long time ago.

Symptoms. At first, the flu may seem like a common cold with a runny nose, sneezing and sore throat. Colds usually develop slowly. But the flu tends to come on suddenly. And while a cold can be miserable, you usually feel much worse with the flu. Common symptoms of the flu include: Fever; Aching muscles; Chills and sweats; Headache; Dry.