H1N1: The "swine flu"

The 2009 outbreak of the H1N1 virus, or "swine flu," and the subsequent development of a vaccine for the disease have recently brought vaccination back to public attention. Some people expressed concerns that the "new" H1N1 vaccine could be untested and unsafe. While it's a good idea to be cautious when it comes to the things that affect your health, the worry over the H1N1 vaccine was unfounded. The vaccine is made in the same factories, with the same ingredients and the same methods as the familiar seasonal flu vaccine, which has proven to be very safe. The only difference is that the swine flu vaccine targets the new viral strain instead of the seasonal flu strains. This H1N1 outbreak has fortunately been less dangerous so far than many people suggested it could have been. Similar viruses have caused worldwide outbreaks in the past, however, killing millions of people, and the speedy development of vaccines is an important part of the strategy for preventing such situations.

Influenza virus: Our immune systems fight viruses by recognizing the proteins covering them, represented on this virus model by the spikes and bumps on its surface. New strains of influenza, like H1N1, have slightly different protein coverings, so vaccines need to be adjusted to match them.
Influenza virus: Our immune systems fight viruses by recognizing the proteins covering them, represented on this virus model by the spikes and bumps on its surface. New strains of influenza, like H1N1, have slightly different protein coverings, so vaccines need to be adjusted to match them.
Courtesy the National Institute of Health