less likely to become infected and transmit those germs to others. Even people who have not been vaccinated may be protected by the immunity of the “herd,” because the vaccinated people around them are not getting sick or transmitting the infection. The higher the proportion of vaccinated people in a community, the lower the likelihood that a susceptible person will come into contact with an infectious individual—leading to greater herd immunity.

In the past, thimerosal, a preservative that contains mercury, was used in some vaccines and other products. Use of this product became the subject of controversy, with some arguing that the substance caused autism in children. Extensive, independent research has presented no convincing evidence of harm associated with the low levels of thimerosal present in vaccines. Since 2001, thimerosal has not been routinely used as a preservative in recommended childhood vaccines.

Antibiotics and Antivirals

Antibiotics are powerful medicines that fight bacterial infections. They either kill bacteria or stop them from reproducing, allowing the body’s natural defenses to eliminate the pathogens. Used properly, antibiotics can save lives. But growing antibiotic resistance is curbing the effectiveness of these drugs. Taking an antibiotic as directed, even after symptoms disappear, is key to curing an infection and preventing the development of resistant bacteria.

Antibiotics don’t work against viral infections such as colds or the flu. In those cases, antiviral drugs, which fight infection either by inhibiting a virus’s ability to reproduce or by strengthening the body’s immune response to the infection, are used. There are several different classes of drugs in the antiviral family, and each is used for specific kinds of viral infections. (Unlike antibacterial drugs, which may cover a wide spectrum of pathogens, antiviral medications are used to treat a narrower range of organisms.) Antiviral drugs are now available to treat a number of viruses, including influenza, HIV, herpes, and hepatitis B. Like bacteria, viruses mutate over time and develop resistance to antiviral drugs.

New Treatments

Modern medicine needs new kinds of antibiotics and antivirals to treat drug-resistant infections. But the pipeline of new drugs is drying up. For example, nearly 40 years elapsed between introduction of the two newest molecular classes of antibiotics: fluoroquinolones (such as Cipro) in 1962 and the oxazolidinones (such as Zyvox) in 2000.

Major pharmaceutical companies have limited interest in dedicating resources to the antibiotics market because these short-course drugs are not as profitable

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