-Vaccine does not work (dead form ineffective, pathogen hides from immune system]
-Vaccine not safe [no weak/active form, causes major side effects]
-Many strains of pathogen
-Cannot achieve herd immunity (logistics of vaccinating large proportions]
-Antigenic variability
![](https://img.wattpad.com/cover/272714285-288-k56915.jpg)
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A-level Biology Notes
General FictionTopics 1-4 of A-level Biology AQA New specification