#21 En este caso no es así, de hecho es todo lo contrario, fíjate en esto:
"Ironically, the advanced state of public hygiene in the U.S. and the rest of the developed world contributed to the polio epidemics of the 20th century. Polio is primarily a disease of infants and children. Before public hygiene developments, infants and young children became exposed to poliovirus, but their symptoms were mild and the exposure provided lasting immunity. With the advent of indoor plumbing and modern ideas about hygiene and sanitation, children were not exposed to the poliovirus in infancy and did not develop natural immunity. As a result, outbreaks of polio began to be seen in the mid-1800s." (http://www.msmr.org/documents/MSMRDiseaseMonograph-Polio-August2004.pdf)
En muchos otros casos sí, la higiene es incluso más importante (o por lo menos más eficiente, al ser mucho más barata) que la vacuna, pero para llegar a la erradicación de enfermedades altamente contagiosas suele ser precisa una vacuna.
#24 ¡No te olvides de la inmunidad de grupo! (http://www.vacunas.org/index.php?option=com_content&task=view&id=8960&Itemid=360)