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Vaccine program efficacy - case studies
Smallpox vaccination
Smallpox is caused by the variola virus
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Variola virus is a human pathogen, with an
incubation period of three weeks, and is spread by droplet infection
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Everyone infected with
smallpox virus is symptomatic
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Global
smallpox eradication was officially certified in December 1979
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During the first part
of the twentieth century, smallpox was largely eradicated in Oceania, North America, and
Europe by widespread vaccination, originally developed by Edward Jenner, using a live
attenuated strain of vaccinia virus, together with strict controls at frontiers
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Despite difficulties, such as cultural barriers, warfare
and transport to remote areas, the ca,again was successful
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A small number of laboratory derived and vaccination associated
cases occurred subsequently
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Concerns about the use of
smallpox by bioterrorists have resulted in countries making contingency plans for the
potential threat, which include the stockpiling of smallpox vaccine
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Poliomyelitis vaccination
Poliomyelitis is caused by poliovirus
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The glycoprotein capsid of the virus comprises four polypeptides, viral protein 1-4
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Laboratory diagnosis
of poliovirus involves cell culture, electron microscopy, and molecular methods
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Currently circulating
wild type viruses are type 1 and 3
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In tropical
countries polio virus is transmitted all year round, whereas in temperate climates poliovirus
was typically transmitted during the summer months
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The incubation period of polio is usually 1-2 weeks but can range
from 3-3- days
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Poliovirus is detectable in the face
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The majority of cases of poliovirus infection are
asymptomatic
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Paralytic poliomyelitis occurs in <1% of those infected
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The case fatality rate of paralytic polio is 2-3%, mortality is due
to paralysis of intercostal muscles and thus respiratory failure
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the PIV was very effective
at reducing the risk of contracting polio
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Disadvantages of IPV include; expensive
to produce, it must be given intravenously thus requiring trained healthcare professionals, as
the virus is killed it does not undergo its usual life cycle as a result only IgG is produced, and
it requires repeated dosing to maintain IgG levels
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Advantages of the OPV include; oral administration which is
cheaper and easier than intravenous administration, relatively cheap to produce, as the virus
is live it undergo its usual life cycle as a result IgG and IgA are produced, gives better
intestinal immunity due to IgA production, and a single dose is sufficient to induce life long
immunity
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The global polio eradication initiative reduced the number of polio
endemic countries, and the fall in poliovirus transmission jn these countries was due to a
new bivalent oral polio vaccine and new ways of delivery of the vaccine
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However, endemic
transmission was still occuring in Pakistan, Nigeria, and Afghanistan
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As part of the endgame strategy of the
eradication program, countries are switching to IPV to avoid circulation of VAPP, and
trivalent OPV has been replaced by bivalent OPV
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Wild type poliovirus type 3 confirmed as eradicated in 2019
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The eradication of polio requires
continual surveillance and strong commitment to vaccination programmes
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Mumps, and rubella vaccination
Rubella is caused by the togavirus, togavirus is a single stranded RNA virus
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The fetus is particularly susceptible to rubella infection when maternal infection
occurs during the first 3 months of pregnancy, as at this time, the heart, brain, eyes, and
ears are being formed and the virus interferes with their development
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Infected fetuses produce their own IgM antibody to rubella virus, which can be detected in
cord and infant blood
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Rubella virus RNA
detection may be carried out in a laboratory to aid with diagnosis
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As it is a live vaccine, the only safe time during
reproductive life is the immediate postpartum period
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Paramyxovirus us a single stranded RNA virus
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Parotitis
(inflammation of the parotid gland) is the most clinical sign of mumps infection
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Complications
of mumps include; meningitis, encephalitis, pancreatitis, and orchitis
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Measles is caused by the paramyxovirus
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Clinical features include; respiratory symptoms, Koplik’s spots and a maculopapular rash
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Nearly all infected individuals develop symptomatic disease
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After infection there is lifelong resistance to reinfection
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Complications of measles are particularly likely among children in resource-poor
countries, due to malnutrition, starvation, and poor medical services
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Detecting measles virus RNA or carrying out a
measles specific IgM assay is helpful in confirming the diagnosis either on blood or saliva
samples
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There is a live
attenuated measles vaccine
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The MMR vaccine was introduced into the
UK childhood vaccination programme in 1988
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The MMR vaccine requires 90% vaccine cover to provide effective herd immunity
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Nevertheless, WHO
has estimated that >134 000 people died from measles in 2015, most of whom were children
under 5
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Following reduced vaccine
uptake
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However, further studies have failed to show an increased
risk of autism after MMR
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Trials of an earlier
vaccine were stopped when it caused intussusception, a rare cause of bowel obstruction
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The vaccine gives 74-87% efficacy
against any rotavirus gastroenteritis, and 85-98% protection against severe gastroenteritis
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