On Sat, 14 Jul 2012 18:31:43 -0700 (PDT), "John H. Gohde"
<
john.h...@gmail.com> wrote:
>
>The oral polio vaccine contains a live polio virus and has been linked
>to polio-like paralysis. Polio vaccines used in other countries do not
>include the live virus, but polio vaccines used in India do.
All oral polio vaccines contain live (attenuated) polio virus. The
rate of actual disease being produced by the oral vaccine is very
small (the vaccine actually *gives* you a case of polio-like infection
(you don't get sick) and this causes natural immunity to full-strength
virus.
An interesting pehnomenon has developed, however, as the number of
polio cases has decreased all over the world; and some have suggested
that in those countries where cases ofpolio are only sporadic, the
injectable (Salk) vaccine be used instead of the oral form (Sabin).
The Wikipedia entry contains the following information about the
vaccines in general:
--------------------------------------------------------
Oral polio vaccine (OPV) is a live-attenuated vaccine, produced by the
passage of the virus through non-human cells at a sub-physiological
temperature, which produces spontaneous mutations in the viral
genome.[32] Oral polio vaccines were developed by several groups, one
of which was led by Albert Sabin. Other groups, led by Hilary
Koprowski and H.R. Cox, developed their own attenuated vaccine
strains. In 1958, the National Institutes of Health created a special
committee on live polio vaccines. The various vaccines were carefully
evaluated for their ability to induce immunity to polio, while
retaining a low incidence of neuropathogenicity in monkeys.
Large-scale clinical trials performed in the Soviet Union in late
1950s — early 1960s by Mikhail Chumakov and his colleagues
demonstrated safety and high efficacy of the vaccine.[33][34] Based on
these results, the Sabin strains were chosen for worldwide
distribution.[13]
There are 57 nucleotide substitutions which distinguish the attenuated
Sabin 1 strain from its virulent parent (the Mahoney serotype), two
nucleotide substitutions attenuate the Sabin 2 strain, and 10
substitutions are involved in attenuating the Sabin 3 strain.[6] The
primary attenuating factor common to all three Sabin vaccines is a
mutation located in the virus's internal ribosome entry site
(IRES)[35] which alters stem-loop structures, and reduces the ability
of poliovirus to translate its RNA template within the host cell.[36]
The attenuated poliovirus in the Sabin vaccine replicates very
efficiently in the gut, the primary site of infection and replication,
but is unable to replicate efficiently within nervous system tissue.
OPV also proved to be superior in administration, eliminating the need
for sterile syringes and making the vaccine more suitable for mass
vaccination campaigns. OPV also provided longer lasting immunity than
the Salk vaccine.
In 1961, type 1 and 2 monovalent oral poliovirus vaccine (MOPV) was
licensed, and in 1962, type 3 MOPV was licensed. In 1963, trivalent
OPV (TOPV) was licensed, and became the vaccine of choice in the
United States and most other countries of the world, largely replacing
the inactivated polio vaccine.[8] A second wave of mass immunizations
led to a further dramatic decline in the number of polio cases.
Between 1962 and 1965 about 100 million Americans (roughly 56% of the
population at that time) received the Sabin vaccine. The result was a
substantial reduction in the number of poliomyelitis cases, even from
the much reduced levels following the introduction of the Salk
vaccine.[37]
OPV is usually provided in vials containing 10-20 doses of vaccine. A
single dose of oral polio vaccine (usually two drops) contains
1,000,000 infectious units of Sabin 1 (effective against PV1), 100,000
infectious units of the Sabin 2 strain, and 600,000 infectious units
of Sabin 3. The vaccine contains small traces of antibiotics— neomycin
and streptomycin—but does not contain preservatives.[38] One dose of
OPV produces immunity to all three poliovirus serotypes in
approximately 50% of recipients.[16] Three doses of live-attenuated
OPV produce protective antibody to all three poliovirus types in more
than 95% of recipients. OPV produces excellent immunity in the
intestine, the primary site of wild poliovirus entry, which helps
prevent infection with wild virus in areas where the virus is
endemic.[30] The live virus used in the vaccine is shed in the stool
and can be spread to others within a community, resulting in
protection against poliomyelitis even in individuals who have not been
directly vaccinated. IPV produces less gastrointestinal immunity than
does OPV, and primarily acts by preventing the virus from entering the
nervous system. In regions without wild poliovirus, inactivated polio
vaccine is the vaccine of choice.[30] In regions with higher incidence
of polio, and thus a different relative risk between efficacy and
reversion of the vaccine to a virulent form, live vaccine is still
used. The live virus also has stringent requirements for transport and
storage, which are a problem in some hot or remote areas. As with
other live-virus vaccines, immunity initiated by OPV is probably
lifelong.[31]
==================================
Best,
Bob
Robert A. Fink, M. D., FACS
Neurological Surgery
Berkeley, California USA
--------------------------------
Note: Nothing in this message should be
considered as "medical advice". Such
advice should only be given after direct
face-to-face contact between physician
and patient.