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View Diary: Baby dies from whooping cough in Orange Co. (79 comments)

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  •  well, mostly.... (0+ / 0-)

    There were 3 strains of polio in the original OPV, tagged Sabin-1, Sabin-2 and Sabin-3.

    Sabin-1 is probably one of the safest vaccines ever. When I left the bioscience field there had never been a recorded incident of an issue attributable to that strain.

    Sabin-2 quickly established immunity in the primary recipient but it was remotely possible for it to revert if the recipient was co-infected with wild-type. With herd immunity established, not a problem.

    Sabin-3 is interesting - also quickly establishes immunity but within a few days if you were to go to an infant that had received their first OPV, sample the contents of every diaper and isolate the type 3 you'd discover that the majority of it had reverted to virulent.

    I worked with the team that performed that research and when we sequenced the RNA genome of those viruses we discovered that the Sabin-3 strain in use at the time differed from wild-type by only 13 point mutations in its 7400-base genome. If a particular one of those 13 reverted (position 172 in the 5' non-coding region if I remember correctly) that was enough to restore the virulence of the virus. One of the major efforts in the lab at the time was to take the ultimately safe Sabin-1 strain and engineer it to have the antigenic regions of type 3 thus producing a type 3 vaccine strain that could not revert.

    It is because of this that the US switched to using an injectable inactivated polio vaccine rather than the OPV.

    •  Always A Concern With RNA Viruses (0+ / 0-)

      Those little genomes mutate like crazy

      There’s always free cheddar in a mousetrap, baby

      by bernardpliers on Sat Apr 27, 2013 at 03:02:04 PM PDT

      [ Parent ]

      •  Exactly. (0+ / 0-)

        Particularly one like this that basically looks like a 7.4kb piece of mRNA, with a single open reading frame. Its replication was far from faithful. The crazy thing with type 3 was with so few point mutations differentiating it from wild-type was just how FAST the little bugger reverted after a vaccine dose was given.

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