Sunday, January 6, 2013


Happy New Year!

Christmas this year was bittersweet. It was Andrew's first Christmas and our first Christmas without my mother-in-law Mary. Holly and I also became homeowners last month, although next Christmas will be our first in our new home.

At his 2 month visit in September, Andrew received Pentacel® (diphtheria, tetanus, acellular pertussis, Hib, IPV) instead of Pediarix®. The Pediarix® he received this visit won't count as Andrew's third and final dose of hepatitis B vaccine, but it saved him an extra poke, since he would have had to have received separate DTaP and IPV shots (Kinrix®, a combination DTaP and IPV vaccine is licensed for children 4 to 6 years of age).


Asymmetric weakness:
The muscles in this man's right
leg are atrophied while his left
leg appears normal.
CDC/NIP/Barbara Rice
The word poliomyelitis means "inflammation of gray marrow" (Greek: polios, gray, + myelos, marrow, + -itis, inflammation) because the poliovirus destroys nerve cells (gray matter) in the spinal cord which transmit impulses from the brain to the muscles. Damage to these cells causes muscle weakness and
paralysis. The virus also destroys nerve cells in the brain. It rarely causes sensory loss.

Paralytic polio typically causes weakness in limb muscles that is greater on one side of the body (asymmetric). Polio can paralyze the diaphragm and muscles in the chest, leaving a person unable to breathe. An "iron lung" is a negative pressure ventilator used to keep people with paralysis of the respiratory muscles alive.

Mr. Barton Hebert used this iron lung from the late 1950s until his death in 2003
Poliovirus is transmitted by the fecal-oral route, which means that the virus is shed in the stool of an infected person and then taken into the mouth with contaminated food, water, or other objects, such as fingers that have touched contaminated surfaces. The virus replicates in the back of the throat (oropharynx) and the intestine and then spreads into the blood (viremia).

Less than 1% of people infected with poliovirus develop paralytic polio. More commonly, infected people develop a minor illness called abortive polio: fever, nausea, vomiting, headache, sore throat, fatigue, and malaise with no neurological abnormalities. A small proportion will develop nonparalytic polio (viral meningitis) or polioencephalitis.

Over 95% of people infected with poliovirus have no symptoms yet still shed the virus and can infect others. Therefore, reported cases of paralytic polio are only the tip of the iceberg of total poliovirus infections.

My great aunt Gertie had polio
as a child. She could walk
using her hands to move her
Polio was declared eliminated from the U.S. in 1979 and certified eliminated from the WHO Region of Americas in 1994. Today, most parents of infants and most doctors in the U.S. have never seen a case of polio. I had a great aunt who had polio as a child. I've seen a few adults in this country with post-polio syndrome, and I've seen children in Africa with atrophied limbs from polio, but I've never seen an acute case of polio. It's easy to forget how terrifying polio was in the pre-vaccine era.

We usually think of improvements in sanitation as reducing the burden of disease. The opposite occurred with polio in the United States. Polio had been an infection that was usually acquired in infancy. Because the infection occurred at a time when babies were still protected by antibodies they received from their mothers while in the womb (passive immunity), few babies developed polio. As sanitation improved, babies were no longer exposed to poliovirus and did not develop their own antibodies to the virus. Children were exposed to poliovirus after they were no longer protected by maternal antibodies and epidemics began to occur.

During the 1916 polio epidemic in New York City over 9,000 people were paralyzed and 2,343 people died from the disease, most of them young children. Police guarded the entrances to nearby Hoboken, New Jersey to prevent people from New York from entering that city. Polio epidemics in the United States increased in size through the first half of the 20th century. In 1952 there were 57,879 cases of polio reported in the U.S. After the introduction of the Salk polio vaccine in 1955, the incidence of polio in the U.S. decreased from 25 cases per 100,000 people every year to 0.4 cases per 100,000 in 1962.

The history of the development of the Salk inactivated polio vaccine and Sabin live oral polio vaccine has been well-documented in books and in the media. I won't go into the details here, but I've included some links to websites below for those who are interested and also recommend Paul Offit's book The Cutter Incident.

Polio vaccines

There are two types of polio vaccines used today, inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV). IPV is a killed-virus vaccine that was developed by Jonas Salk and licensed for use in the U.S. in 1955. IPV is currently the only polio vaccine used in the U.S. It is administered by injection and is both highly effective and safe.

Oral poliovirus vaccine contains live attenuated (weakened) poliovirus. Because the vaccine virus replicates in the throat and in the intestine, it causes a better production of immunoglobulin A (IgA), an antibody found on mucosal surfaces, than IPV. Vaccine virus is also shed in stool and can be transferred to close contacts of vaccine recipients. OPV was used in the U.S. from the early 1960s until the late 1990s.

Administering OPV in Gorakhpur, India
CDC/Chris Zahniser
OPV is highly effective, inexpensive, and can be administered by non-medical personnel. There is also a 1 in 2.4 million dose risk of vaccine-associated paralytic polio (VAPP). There were 144 cases of VAPP in the U.S. between 1980 and 1998. Because the risk of VAPP outweighed the risk of wild poliovirus infection in the U.S., the CDC's Advisory Committee on Immunization Practices (ACIP) first recommended using a sequential IPV-OPV schedule to reduce the risk of VAPP in 1996 and then an all IPV schedule in 1999. Although OPV is no longer used in this country, the federal government maintains a stockpile of OPV to use for mass immunization if there is ever an outbreak of polio in this country.

OPV is used in countries where polio remains endemic or where the risk of importation is greater than the risk of VAPP.

In 1988, the World Health Assembly passed a resolution to eradicate polio. At that time, there were an estimated 350,000 cases of polio per year in over 125 countries. Today there are only three countries in which polio remains endemic; Afghanistan, Pakistan, and Nigeria.

Polio cases in the world in 2012
Afghanistan, Pakistan, and Nigeria are the last remaining polio-endemic countries. Last year, polio was imported from Nigeria to Chad and Niger, where transmission had been interrupted.
Global Polio Eradication Initiative

We are closer than ever to eradicating polio from the world forever.

Songwriters Robert and Richard Sherman wrote "A Spoonful of Sugar" for the 1964 movie Mary Poppins after Robert heard that his children had received oral polio vaccine on a sugar cube.

President Franklin Delano Roosevelt founded the National Foundation for Infantile Paralysis, now known as the March of Dimes Foundation, to fund polio vaccine research. The U.S. ten cent piece (dime) bears his image for this reason. Roosevelt contracted polio at the age of 39.

More information
Regina Edwards, 1952
March of Dimes

Centers for Disease Control and Prevention. (2000). Poliomyelitis prevention in the United States: updated recommendations of the Advisory Committee on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 49(5), 1-22.

Centers for Disease Control and Prevention. (2012). Epidemiology and prevention of vaccine-preventable diseases (12th Ed.). Washington D.C.: Public Health Foundation.

Malonado, Y. A. (2009). Polioviruses. In S. S. Long (Ed.) Principles and practice of pediatric infectious diseases (3rd Ed.) [Electronic version].

Modlin, J. F. (2009). Poliovirus. In Mandell, G. L., Bennett, J. E., & Dolin, R. (Eds.). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases. (7th Ed.) [Electronic version].

Offit, P. A. (2005). The Cutter incident: how America's first polio vaccine led to the growing vaccine crisis. New Haven: Yale University Press.

Plotkin, S. A. & Vidor, E. (2012). Poliovirus vaccine-inactivated. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (6th Ed.). [Electronic version].

Sutter, R. W., Kew, O. M., & Cochi, S. L. (2012). Poliovirus vaccine-live. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (6th Ed.). [Electronic version].

World Health Organization. (2013). Poliomyelitis fact sheet.