The Centers for Disease Control and Prevention sets the US vaccination schedule. Some of the vaccines, like Hepatitis B, are administered once. Others, like the flu vaccine, are needed each year.
If you’re not sure about whether you’re immunized, you can ask your doctor for a blood test that will give an answer within a couple of days.
The CDC schedule is based on the occurrence of someone becomes seriously susceptible to each disease on the list. Researchers say people who delay vaccinations are a public health risk, as they put off vaccines that are timed according to the best-available science to keep babies healthy.
“There is just no science to” delaying vaccinations, Doug Opel, a Seattle pediatrician who studies vaccines, told Vox’s Julia Belluz. “We immunize with this vaccine at this time because kids are most at risk at this point. They are most susceptible. What gets lost a lot of the time is that there’s an incredible amount of data underlying the recommended schedule.”
For more detailed information, check out the CDC’s website and talk to your doctor.