Polio Eradication

Question 1

What is the IPV, how is it administered, and what are its advantages and disadvantages?

Answer 1

Inactivated Polio Vaccine (Salk vaccine)
Killed wild type virus, 
Intramuscular administration
No vaccine-associated disease
Systemic IgG response, 

Little mucosal protection (no IgA response)
More expensive than oral vaccine

Question 2

What is the OPV, how is it administered, and what are its advantages and disadvantages?

Answer 2

Oral Polio Vaccine (Sabin vaccine)
Live attenuated poliovirus
Oral Administration
Inexpensive
Systemic immunity
IgA response, good mucosal protection

Shed revertant poliovirus
Vaccine-Associated Paralytic Poliomyelitis (VAPP)
Contraindicated in immunocompromised
Source of circulating Vaccine Derived Polio Virus (Can cause polio in un-vaccinated)

Question 3

Eradication

Answer 3

No need for ongoing polio vaccinations

Establish that eradication is a good public health strategy

Question 4

Who established the March of Dimes in 1938?

Answer 4

Franklin Roosevelt

Question 5

What kind of virus is Poliovirus?

Answer 5

Picornavirus

Question 6

Who still receives small pox vaccinations?

Answer 6

US military personnel

Question 7

Why is the oral polio vaccine used so widely?

Answer 7

Cost per dose is $0.13,

IVP is $1.50 per dose, 10x more

Question 8

IPV vaccinated children may remain healthy despite being infected with poliovirus due to what?

Answer 8

Anti-polio IgG

Polio virus may still infect mucosal surfaces and be shed from them to infect others.

Question 9

What advantage does IPV have over OPV

Answer 9

Does not lead to VAPP

Question 10

What immune response does OPV create?

Answer 10

IgA

Question 11

Life cycle of guinea worm

Answer 11

Worms escape from sores on human feet
Disgorge eggs into water supply
Larvae infect water fleas
Water fleas are injested by humans drinking the water
Larvae escape human digestive tract and grow
10-14 months later, worms emerge from sores on feet

Question 12

How can guinea worm be eradicated without vaccines?

Answer 12

Safe drinking water

Question 13

Why is eradication of poliovirus a rational goal?

Answer 13

Polio only infects humans
There is an effective and affordable vaccine available
Mucosal immunity prevents transmission
Virus can only survive for days or weeks outside human host

Question 14

What condition is used to track the location of polio?

Answer 14

Most polio infections are asymptomatic. Some present as Acute Flaccid Paralysis, thus AFP is the used as a sign of possible polio infection.
Viruses other than polio may also cause AFP.

Question 15

What defines polio-free certification?

Answer 15

2-3 years of high quality AFP surveillance without the detection of any wild type poliovirus

Question 16

How many doses are used each year in polio eradication efforts?

Answer 16

1-2 Billion doses
At 13 cents per dose, this is ~$300 million dollars
Total costs are ~$1 billion per year, or equivalent to CUSOM budget

Question 17

What viruses other than Polio cause AFP?

Answer 17

Coxsackie A
Coxsackie B
Enterovirus 71
ECHO viruses

Question 18

Why is OPV used more frequently than IPV in
countries with wildtype poliovirus
transmission?

Answer 18

OPV is cheaper than IPV.
OPV induces better mucosal immunity than IPV.
Immunity from OPV stops wild type virus transmission more effectively than immunity from IPV.
OPV can be administered by almost anyone whereas IPV
requires needles & personnel who can use needles safely.

Question 19

Why is the bivalent OPV more effective than the trivalent OPV in inducing protection against PV Serotype 1?

Answer 19

Because the OPV is live vaccine, type 1 has to compete with type 2 & 3 to infect cells. PV Serotype 1 has more attenuating mutations than type 2 and 3 and is less competitive, leading to a lower viral load and lower probability of inducing an effective immune response.

Question 20

When compared to tOPV, bOPV1&3 has better efficacy

against which serotype?

Answer 20

Serotype 1

Question 21

What does VDPV mean and how do they arise?

Answer 21

Vaccine Derived Polio Virus
The oral vaccine uses live viruses that have been mutated to the point that they do not cause disease in the infected person. However, these viruses continue to be shed from immunized persons for some period of time, and occasionally revert to more virulent forms. Thus, unvaccinated or immunocompromised persons may become infected and suffer the consequences of polio virus derived from the attenuated strains.

Question 22

Which serotypes (1, 2, or 3) revert and cause circulating VDPV?

Answer 22

Serotypes 1, 2 and 3 all revert and cause cVDPV

Question 23

Approximately what percent of a circulating virus’s genome will mutate each year?

Answer 23

1%
Thus, if a virus is 3% different from an OPV strain, it can be estimated to have circulated for 3 years.
This is all due to the error-prone viral polymerase, and most of the mutations occur at the 3rd/”wobble” position of the codon producing silent mutations.