OMIKRON / SCIENCE PHOTO LIBRARY OMIKRON / SCIENCE PHOTO LIBRARY
False-colour transmission electron micrograph (TEM) of a field of polio virus particles (virions), the cause of poliomyelitis. Polio virions are small (20-30 nanometers diameter) & have a simple structure, containing only one type of nucleic acid, RNA. The virions are not surrounded by a lipoprotein envelope, as other larger & more complex viruses are. Vaccines which confer immunity against polio fall into 2 types; inactivated viral vaccines, eg the Salk polio vaccine, & living vaccines from less virulent viral mutants, eg the non-paralytic strain of poliovirus vaccine (Sabin). Magnification: x20,000 at 35mm size.
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