Vaccines are big news right now. All over town you can find places delivering the normal, seasonal flu vaccine – everywhere from the county health clinic to the local drugstore. There is also a lot of buzz around the special H1N1 vaccine – millions of people are being vaccinated. There is currently an outbreak of the mumps in Brooklyn and surrounding areas because people there weren’t vaccinated properly.

At the root of all this is a simple and fascinating technology that takes advantage of a special property of the human immune system. We can understand how it works by looking at the world’s first vaccine.

If we could go back in time to the 1700s, the world was a very different place. Infectious diseases ran rampant. Mumps, measles and polio were obvious problems, but there was also a scourge called smallpox. It killed millions. It left many people blind. And those who survived the disease were often left with disfiguring scars from the disease’s pustules. These scars have been found on the faces of Egyptian mummies, so we know the disease is thousands of years old.

There was, however, a group of people who seemed to be untouched by smallpox. These people were known as milkmaids – women who milked cows for a living. Their immunity to smallpox was obvious because of their smooth skin. A scientist named Edward Jenner noticed this, and hypothesized that the women were being protected by exposure to cowpox. In other words, the women were getting infected with cowpox, which is a much milder disease than smallpox. Once the women recovered from cowpox, they had somehow acquired immunity to smallpox.

Jenner’s breakthrough idea was this: if he were to purposefully infect people with cowpox at a young age, he would be able to protect them from smallpox. Jenner called the process vaccination – vacca being the Latin word for cow. James Phipps was the first boy to be vaccinated. Jenner made a small cut on his skin and inserted pus from a cowpox lesion. The boy did get sick with cowpox, and then recovered normally. And he became immune to smallpox in the process. The rest, as they say, is history. The process of vaccination was improved and refined, to the point where today the disease known as smallpox has been completely eradicated. This video shows how the cowpox vaccine was created in the 1950s – not a huge change from Jenner’s time:

Why did this work? Jenner had no concept of the actual mechanisms. It would be more than 100 years before scientists discovered viruses. But the mechanism is the basis of all vaccines today. When a human being is infected by any viral disease, the human immune system has to discover and eliminate the virus. Virus particles are extremely small – much smaller than bacteria cells, which are themselves a hundred times smaller than human cells. The virus particles attach to human cells, inject a tiny bit of genetic material and force the cells to manufacture millions of new virus particles.

To eliminate a virus, white blood cells in your body produce antibodies. Antibodies are molecules that cling to virus particles and deactivate them – the antibodies attached to the virus particles keep the virus particles from being able to dock onto human cells. The clinging antibodies also act like beacons that make it easy for the body to eliminate the virus particles. However, the body does not make antibodies for a specific virus until it gets exposed to the virus. This is why most viral diseases are only caught once in a lifetime.

The idea behind any vaccine, therefore, is to pre-expose the body to a form of the virus so that the body is already producing antibodies when the real virus comes along. In the case of smallpox, it turned out that the cowpox virus particles are nearly identical to smallpox virus particles – so close that cowpox antibodies also cling to smallpox virus particles. Once exposed to cowpox, the same antibodies would attack smallpox too. Other vaccines deliver dead virus particles. The body learns to produce antibodies against the dead virus, and then when it sees live virus particles it eliminates them immediately. All vaccines work on this same basic principle, exposing the immune system to the disease in some way so the body learns to produce antibodies. Those antibodies then confer protection against the real disease.

Are vaccines something to be afraid of? Obviously not. We should be far more fearful of the diseases they prevent. Vaccines have made our world a much better place, and when used widely can completely eliminate dangerous and deadly viruses like smallpox.

See also:
- Good question – how do you catch the flu?
- How to avoid catching a cold
- How Swine Flu Works
- How Vaccines Really Work -or- we need to completely ignore the anti-vax crowd