(FORTUNE Magazine) – Anthrax is today's big story. Tomorrow's could be smallpox--a highly contagious disease that's fatal 30% of the time. There's no treatment for smallpox. The good news, such as it is, is this: If a smallpox vaccine is administered within four days of exposure, it can prevent the disease from occurring or reduce its severity.

And therein lies the beauty of vaccines, all of which contain part of a bacteria or a virus. When injected or taken orally, they induce immunity. Recent decades may have found us taking vaccines for granted, but anyone who has been around a while knows about the scores of children paralyzed by polio and the millions of people throughout the world who died in the influenza pandemic of 1918-19.

Vaccinations are cost-effective. Up to $14 is saved for every dollar spent. Despite this, millions of people don't receive appropriate immunizations.

Some view them as unnecessary because the targeted diseases are uncommon. But even when the risk is low, the stakes are high. A man I once treated for tetanus was in intensive care for two months; we had to paralyze him in order to stop the tetanus spasms and put him on a ventilator to help him breathe. A simple shot might have prevented all that.

Immunizations are generally effective, but not perfect. For example, the pneumonia vaccine contains 23 strains of streptococcus that cause 10% to 15% of adult pneumonia. The vaccine won't prevent pneumonia caused by other strains or other organisms, but it is 60% effective against those 23.

Generally, vaccinations are safe. Local reactions (swelling and pain at the injection site) are the most common adverse events and occur up to 50% of the time. Only very rarely does someone have a severe allergic reaction.

Provided you've received your childhood shots, here is an abbreviated list of immunizations adults should consider.

Anthrax. It's generally safe and over 90% effective, but the vaccine is in short supply and we won't have enough for some time. Until then, it's reserved for the military and other high-risk groups. Also, it's not quick--six doses over 18 months, then yearly boosters.

Smallpox. There hasn't been a case of smallpox in the U.S. for over 50 years and the last known case in the world occurred in 1977, but recent events have everyone worried. The government has 15 million doses of vaccine in storage. In addition, production is being ramped up (the goal is to have 300 million doses stockpiled by next year), and a diluted vaccine is being tested to see if it's effective.

Tetanus/diphtheria. Should be given every ten years for everyone. If you suffer a dirty wound, you need a shot if five years have passed.

Pneumonia. At age 65 or earlier for adults with diabetes or heart, lung, or other chronic disease. Revaccination is recommended after five years for people at high risk.

Influenza. Yearly after age 50 and for health-care workers or people with chronic diseases. Studies have shown this vaccine can decrease absenteeism among the work force, so everyone should consider it.

Rubella. Women of childbearing age should have their rubella immunization status checked prior to conception, then get a shot if they're not immune.

Hepatitis A. For people who travel to high-risk areas of the world, those with chronic liver disease, or homosexuals.

Hepatitis B. More adults are killed by hepatitis B virus each year than by any other vaccine-preventable disease. Hepatitis B, similar to HIV, is transmitted through blood and body secretions. The vaccine is recommended for all high-risk adults (including homosexuals, intravenous drug users, and health-care personnel). A new vaccine has just been approved that offers protection against hepatitis A and hepatitis B.

Chickenpox. Any adult who hasn't had chickenpox or a chickenpox vaccination should receive the vaccine. Chickenpox is very serious if contracted as an adult.

Lyme disease. People who live in areas where the disease exists should consider vaccination. It's about 80% effective after a series of three shots.

Routine immunizations are easy to forget. If you fit into any of the above categories, talk to your health-care provider. A simple shot may prevent a disease that could kill you.

For more information on this topic: Go to mayoclinic.com. Mayo Clinic offers Executive Health programs at Mayo Clinics in Jacksonville, Fla.; Rochester, Minn.; and Scottsdale, Ariz.