As summer winds down, students from kindergarten to college are heading off to new schools, with lots of new people to meet—and new germs to catch. It’s a perfect time to start planning to protect your health. One of the best ways to guard you and your family against infectious disease is to stay up-to-date with your vaccines.

Thanks to medical research, many of us have never known the terrible diseases that immunization keeps at bay. Before vaccines, polio paralyzed thousands of children nationwide every year, and measles infected millions. At the turn of the 20th century, diphtheria was one of the most common causes of death in school-age children. Today, these are best known as the names of shots our kids get at the pediatrician’s office. Cases of vaccine-preventable diseases have reached an all-time low, according to a recent report from the U.S. Centers for Disease Control and Prevention.

But because we rarely, if ever, see childhood diseases like diphtheria and whooping cough, some people question whether the vaccines are necessary. Others worry about possible links between vaccines and illness. The scientific evidence to date doesn’t support such concerns, however, and public health officials agree that the benefits of vaccination far outweigh the risks.

Vaccines prime the body to defend itself against pathogens. Early vaccines contained weakened live pathogens, but most now consist of a part of a pathogen or a crippled pathogen. When you get a vaccine, the immune system goes into action, ramping up production of specialized cells and antibodies to fight what the body sees as an invading pathogen. If the body later encounters the real pathogen, it “remembers” it and quickly gets rid of it.

Staying up-to-date on vaccines doesn’t just help you. When more people are vaccinated in a population, it’s harder for pathogens to spread. Scientists call this the “herd-immunity” effect.

Many vaccines protect us against viruses. Viruses need a host—like the body of a human, animal or plant—to make copies of themselves. Viruses have their own genetic material but use the host’s cells to multiply. Some viruses constantly change their genetic material, allowing them to evade immune system attack. That’s why researchers who create vaccines for seasonal influenza, or “flu,” have to make a new flu vaccine each year.

To make effective flu vaccines, researchers pay close attention to how and when the flu virus changes. Dr. Derek J. Smith, an NIH-funded researcher from the University of Cambridge in England, recently developed a new technique, called antigenic cartography, that will help guide vaccine development. It involves testing how strongly thousands of flu strains attach to various human antibodies. This information is then compared to a world map to trace how flu viruses evolve and spread throughout the year.

Smith’s team has learned that the most common type of flu starts a predictable, yearly journey in East and Southeast Asia, then travels around the world and ends up in South America. In addition to improving the effectiveness of the flu vaccine, Smith says his method may help scientists develop vaccines against some of the world’s craftiest and deadliest viruses. “Antigenic cartography should be applicable to other infectious diseases caused by pathogens that change over time, such as hepatitis C, HIV and malaria,” he says.

Along with improving current vaccines, scientists are also working hard to develop new ones. In 2006, the vaccine Zostavax was approved by the U.S. Food and Drug Administration to protect older adults against shingles, an illness caused by the same virus that causes chickenpox. The virus can lay dormant in nerve cells for many years, only to re-emerge years later as a painful, blistery rash. Because shingles pain can be severe and long-lasting, most doctors recommend that older adults get the vaccine. It’s not 100% effective at preventing shingles, but can prevent most cases of severe pain.

Vaccines may one day help protect us against cancer as well. Scientists know that about 1 in 5 cancers are caused by infectious agents, says Dr. Douglas Lowy of NIH’s National Cancer Institute (NCI). “Identifying these infectious agents can, in principle, lead to the prevention of these cancers if vaccines can be developed against them,” Lowy says.

After scientists linked a virus called HPV with virtually all cases of cervical cancer in women, Lowy took part in an international effort whose findings led to an HPV vaccine. This vaccine, Gardasil, protects against the types of HPV that cause 70% of all cervical cancers and 90% of genital warts. A second HPV vaccine in development, Cervarix, also targets the main cancer-causing HPVs.

Viruses and bacteria have been linked to stomach and liver cancers as well. For example, hepatitis viruses, which can cause liver scarring and failure, can also lead to liver cancer. There’s currently an FDA-approved vaccine against the hepatitis B virus, but not one against hepatitis C, another important cause of liver cancer.

Researchers are hoping one day to be able to use vaccines to treat disease after it has already struck. Still experimental, these so-called therapeutic vaccines work by stimulating the immune system to recognize and attack diseased cells without harming healthy ones. Researchers are now testing these types of vaccines against several different cancers.

“These vaccines enhance a patient’s own immune system to fight his or her tumor,” says Dr. Jeffrey Schlom, who is currently developing and testing cancer vaccines at NCI.

History has already shown us that immunization is a very successful and cost-effective public health strategy. While new vaccines are in the pipeline, make sure to arm yourself and your children with the ones we already have.