The figures show that immigration trends are forming a unique generational divide: those immigrants over 40 are largely white, while those under 40 are increasingly Hispanic, Asian and from other minority groups.

Maria Fernandez, 42, of Cancun, Mexico, sits outside a shoddy trailer she shares with other workers. "Everybody around here always has headaches, coughs, running noses," she said. "It has to do with that dust on the plants from the chemicals. You are always breathing it in."

The Pepin Comic Book series covers seven immunization topics: Td, Chickenpox, MMR, DTaP, Hep A, Hep B, and After the Shot. These low literate, popular education materials are available in English and Spanish to help clinicians educate parents about the importance of getting their children vaccinated.

Since many exposures come during those field applications, the risks - to farmworkers and to nearby residents who can be affected if the chemicals drift - can occur much more frequently. "You are working in one field, and the tractor passes in the next field spraying," says Epifanio, 58, a veteran Mexican farmworker who asked that his full name not be used, out of fear for his job. "The wind brings it to you. It happens to somebody around here every single day."