A Pakistani health worker administers the oral polio vaccine to a child during a campaign in Karachi on May 7. Because of past attacks on vaccinators, security personnel are often assigned to accompany them.
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A girl is vaccinated against dengue as part of a public immunization program for children in the Philippines. The program was suspended after the company raised safety concerns about the vaccination.
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The American College of Obstetricians and Gynecologists calls the flu vaccine an "essential" part of prenatal care, for protection of the newborn as well as the woman. Infants typically don't get their own flu shot until age 6 months or later.
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A vaccine against heroin wouldn't be like the measles vaccine that you receive once for a lifetime of immunity, say scientists working on it. Multiple shots per year would likely be required, and it would be specific to just heroin and morphine.
A Sudanese nurse prepares an inoculation against measles. In the case of the children who died or were sickened from the vaccine, untrained personnel administered it.
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This year's flu vaccine protects against a few different virus strains, including the H1N1 seen here. The fuzzy outer layer is made of proteins that allow the virus to attach to human cells.
Two polio cases have been reported in Ukraine, where some parents are fearful of vaccinations. Above: A child receives the diphtheria, whooping cough and tetanus vaccine in a children's hospital in Kiev.