A young boy receives an oral polio vaccination at a USAID -funded medical clinic on July 13, 2010 in Petionville, Haiti.  In 2011 in Haiti, the U.S. Government  vaccinated nearly 157,000 children under the age of one for routine childhood diseases and provided more than 350,000 antenatal care visits and more than 131,000 post-partum/newborn care visits.  The United States is providing access to health services for 50 percent of the people of Haiti.  Kendra Helmer/USAID

A young boy receives an oral polio vaccination at a USAID-funded medical clinic on July 13, 2010 in Petionville, Haiti. In 2011 in Haiti, the U.S. Government vaccinated nearly 157,000 children under the age of 1 for routine childhood diseases. / Kendra Helmer, USAID

Immunization is one of the most powerful health interventions ever introduced. Every year, the World Health Organization estimates, vaccines save between 2 and 3 million children from killers such as polio, measles, pneumonia, and rotavirus diarrhea.

To mark World Immunization Week, USAID partner PATH is reporting on the lifesaving potential of vaccines against four illnesses that kill more than 2 million young children a year: malaria, pneumonia, rotavirus, and Japanese encephalitis. Here, Dr. John Boslego, director of PATH’s Vaccine Development Program, lists the top 10 ways vaccines make a difference for children and for global health. This post originally appeared on PATH.

No. 10: Vaccines lower the risk of getting other diseases.

Contracting some diseases can make getting other ones easier. For example, being sick with influenza can make you more vulnerable to pneumonia caused by other organisms. The best way to avoid coinfections is to prevent the initial infection through vaccination.

Here a Nepalese boy demonstrates the water flow of a USAID-built electric tube well used for irrigation in the Terai region of Nepal. Patrick D Smith/USAID

A Nepalese boy demonstrates the water flow of a USAID-built electric tube well used for irrigation in the Terai region of Nepal. / Patrick D Smith, USAID

No. 9: They keep people healthier longer.

Some vaccines protect people for a limited time and require booster doses; others protect for a lifetime. Either way, vaccinated people are much safer from many serious diseases than people who haven’t been vaccinated, both in the short and long term.

As part of a USAID-supported polio initiative, a vaccinator in the Democratic Republic of Congo (DRC) administers the oral polio vaccine March 23 in the Commune of Ndjili, Kinshasa. On that day, Minister of Health, Victor Makwenge Kaput officially launched a vaccination campaign against the wild polio virus in the capital city. USAID/A. Mukeba

As part of a USAID-supported polio initiative, a vaccinator in the Democratic Republic of Congo administers the oral polio vaccine in the Commune of Ndjili, Kinshasa. / USAID, A. Mukeba

No. 8: They are relatively easy to deliver.

Through national immunization programs and mass vaccination campaigns, vaccines can be delivered quickly to large numbers of people, providing widespread protection. Thanks to creative strategies, delivery in even the remotest parts of the world is becoming easier.

USAID and the Medical Relief International Charity (Merlin) support cholera treatment centers in Goma, Democratic Republic of Congo.  Pictured is a young child suffering from cholera and receiving food aid from the Agency.  /  Frederic Courbet

USAID and the Medical Relief International Charity (Merlin) support cholera treatment centers in Goma, Democratic Republic of Congo. Pictured is a young child suffering from cholera and receiving food aid from the Agency. / Frederic Courbet

No. 7: They prevent disease where medical care isn’t an option.

Too many children die because high-quality care is unavailable. When a child in poverty gets sick, medical care could be inadequate or several days’ travel away. Stopping disease before it starts could be that child’s only lifeline.

Solar lights funded by OTI in Cap Haitien and en route to Caracol, Haiti, on Oct. 19, 2012.. / Kendra Helmer/USAID

Solar lights funded by USAID help children read at night in Cap Haitien. Haiti, on Oct. 19, 2012. / Kendra Helmer, USAID

No. 6: They play well with other interventions.

Vaccines complement other global health tools. We’re seeing this with the integrated strategy to protect, prevent, and treat pneumonia and diarrhea through basic sanitation, safe drinking water, hand-washing, nutrition, antibiotics, breastfeeding, clean cook stoves, antibiotics, zinc, oral rehydration solution, and vaccines. Leveraging these tools across diseases could save the lives of over 2 million children by 2015.

This photo took third place in the FrontLines photo contest. Maamohelang  Hlaha tenderly kisses her young son Rebone. An HIV-positive mother of four, Hlaha’s  village is inaccessible by vehicles and a three-hour hike from the nearest health clinic.  She receives HIV treatment through the Riders for Health program, which is funded  by USAID and run by the Elizabeth Glaser Pediatric AIDS Foundation. As part of the  program, pony riders and motorcycle riders transport blood tests, drugs and supplies to  Lesotho’s remote mountain health clinics. The system allows people to receive HIV test  results sooner, access life-saving drugs and ensure an uninterrupted supply of medication.  Rebone, whose name means “we have witnessed,” was born HIV-free in August 2008. / Reverie Zurba, USAID/South Africa

A mother of four who receives HIV treatment through a USAID-funded program tenderly kisses her young son in South Africa. Thanks to the treatment, her son was born HIV-free in August 2008. / Reverie Zurba, USAID

No. 5: They continue to evolve.

Tackling unmet health needs requires us to continue to pursue the next generation of better and more affordable vaccines. Candidates like RTS,S for malaria and ROTAVAC® for the leading cause of severe diarrhea—rotavirus—are two examples of innovative technologies on the horizon that give families and communities more cause for hope.

This photo was chosen as a finalist in the FrontLines photo contest. These schoolchildren in Aqaba, Jordan, are beneficiaries of the Jordan Schools Program and  Education Reform Support Program. Both of these projects are funded by USAID to  support the Jordanian Ministry of Education’s reform efforts in improving the quality of education in the country. March 2011. / Jill Meeks, Creative Associates International

These schoolchildren in Aqaba, Jordan, are beneficiaries the Jordan Schools Program and Education Reform Support Program. Both  are funded by USAID to support Jordan’s efforts to improve the quality of education in the country.  / Jill Meeks, Creative Associates International

No. 4:  They indirectly protect loved ones and communities.

For many diseases, immunizing a significant portion of a population can break the chain of transmission and actually protect unvaccinated people—a bonus effect called herd immunity. The trick is immunizing enough people to ensure that transmission can’t gather momentum.

A little girl in Tajikistan eats mashed potatoes with greens, which her mother prepared for her. Over 5,000 Tajik children under 5 years old tasted new foods such as pancakes ("blini") with cottage cheese and vegetable salads that their mothers prepared for them after a training. / USAID

A little girl in Tajikistan eats mashed potatoes with greens, which her mother prepared for her. Over 5,000 Tajik children under 5 years old tasted new foods such as pancakes (“blini”) with cottage cheese and vegetable salads that their mothers prepared for them after a USAID-supported nutrition training. / USAID

No 3: They are safe and effective.

Vaccines are among the safest products in medicine and undergo rigorous testing to ensure they work and are safe. Their benefits far outweigh their risks (which are minimal), especially when compared to the dire consequences of the diseases they prevent. Vaccines can take some pretty terrible diseases entirely or nearly out of the picture, too. That’s the case with smallpox and polio, and others will follow.

School girls in Sana’a gather for their lesson. Since many girls in Yemen do not attend primary school or graduate from it, recent USAID-backed measures have ensured all girls a right to attend school and increase literacy. / Malak Shaher, USAID/YMEP

School girls in Sana’a gather for their lesson. Since many girls in Yemen do not attend primary school or graduate from it, recent USAID-backed measures have ensured all girls a right to attend school and increase literacy. / Clinton Doggett, USAID

No. 2:  They are a public health best buy.

Preventing disease is less expensive than treating severe illness, and vaccines are the most cost-effective prevention option out there. Less disease frees up health care resources and saves on medical expenditures. Healthier children also do better developmentally, especially in school, and give parents more time to be productive at home and at work.

This image captured top honors in the FrontLines photo contest. These rural schoolchildren participate in the USAID-funded Southern Sudan Interactive Radio Instruction project, which uses radio to broadcast interactive student lessons. The lessons, based on Southern Sudan’s primary school syllabus, complement classroom instruction in literacy, English, mathematics, and life skills for grades one through four. July 2010. / Karl Grobl, Education Development Center Inc.

These rural schoolchildren participate in the USAID-funded Southern Sudan Interactive Radio Instruction project, which uses radio to broadcast interactive student lessons. The lessons, based on Southern Sudan’s primary school syllabus, complement classroom instruction in literacy, English, mathematics, and life skills for grades one through four. July 2010. / Karl Grobl, Education Development Center Inc.

No. 1:  They save children’s lives.

Roughly 2 to 3 million per year, in fact. In short, vaccines enable more children to see their 5th birthdays, let alone adulthood. That’s reason enough to top my list.