Fase preclínica: Se experimenta la eficacia y tolerancia en animales que pueden ser
ratones o monos. Los resultados sirven de apoyo en la investigación posterior que se
realiza en humanos. Los estudios preclínicos usan sistemas de cultivos de tejidos o
cultivos de células y pruebas en los animales para evaluar la seguridad de la vacuna
candidata y su capacidad para inmunizar (proteger) frente a la enfermedad.
• Fase I: Usualmente, se prueba una nueva vacuna en etapa experimental en un
pequeño número de humanos, en general menos de 100 adultos, con el objetivo
de evaluar inicialmente su seguridad y sus efectos biológicos, incluida la capacidad
para estar inmune frente a la enfermedad. Esta fase puede incluir estudios de dosis
y vías de administración (oral, intramuscular y subcutánea).
• Fase II: Prueba una vacuna que fue considerada segura en la Fase I y que necesita un
grupo más grande de humanos (generalmente entre 200 y 500) para monitorear la
seguridad y, también, los ensayos que determinan la eficacia de la vacuna. Las metas
de las pruebas de fase II son estudiar la vacuna candidata en cuanto a su seguridad,
capacidad para inmunizar, dosis propuestas, y método de administración.
• Fase III: Tiene como objetivo evaluar de forma más completa la seguridad y la
eficacia en la prevención de las enfermedades. Esta etapa involucra una mayor
cantidad de voluntarios que participan en un estudio adecuadamente controlado.
Pueden incluir cientos de miles de humanos en un país o varios países. Las pruebas
de fase III son aleatorias (al azar) e involucran dos grupos de personas: uno recibe la
vacuna experimental que está a prueba y el otro recibe un placebo (puede ser una
solución salina, una vacuna para otra enfermedad o alguna otra sustancia). Luego,
se compara los resultados de ambos grupos. En general, la fase III es el paso anterior
a la aprobación de una vacuna.
• Fase IV: Comprende estudios que se realizan después de la aprobación de una vacuna
en uno o varios países. Estas investigaciones tienen como objetivo evaluar cómo
funciona la vacuna en el “mundo real”. En general, son los estudios de efectividad,
también, se siguen monitoreando los efectos adversos en resumen
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