Polio is caused by infection with the poliovirus, which resides in the intestines and is excreted in the stool of infected individuals. The infection occurs only in humans and is transmitted from person to person through food or water contaminated with the poliovirus. Most infected individuals, about 95%, show no symptoms or may have mild illness, but it can be severe enough to cause paralysis of the respiratory system… and can lead to death.
Symptoms of Poliovirus Infection
More than 95% of infected individuals show no symptoms or may have mild, nonspecific illness such as low-grade fever, sore throat, and improvement within 2-3 days. However, some cases may develop headache, nausea, vomiting, and neck pain later on and then recover normally. A small percentage of infected individuals, about 0.1-2%, may experience severe symptoms such as encephalitis, acute flaccid paralysis (AFP) of the limbs, and may develop paralysis of the respiratory system leading to death.
Currently Available Polio Vaccines
- Oral vaccine: This vaccine is prepared from live attenuated poliovirus that cannot cause disease in individuals with normal immunity. Since it stimulates immunity by mimicking natural poliovirus infection, it provides immunity both in the intestines and in the blood.
- Injectable vaccine: This vaccine is prepared from inactivated poliovirus, providing immunity specifically in the bloodstream. Currently, injectable polio vaccines are available both as single vaccines and combined vaccines with others, such as diphtheria-pertussis-tetanus-polio vaccine, diphtheria-pertussis-tetanus-polio-Hib vaccine, etc.
Who “Should” Receive the Polio Vaccine
- All Thai children: Polio vaccine is a basic vaccine that all Thai children must receive, totaling 5 doses at ages 2, 4, 6, 18 months, and 6 years.
- Adults living in areas without polio outbreaks who will travel to areas with polio outbreaks.
- Individuals working in laboratories with potential direct exposure to poliovirus.
Who “Should Avoid” Receiving the Polio Vaccine
- Oral vaccine should not be given to individuals in the following groups:
- Those with immunodeficiency; in such cases, the injectable vaccine is recommended instead.
- Those living in the same household with immunodeficient individuals.
- Pregnant women.
- Injectable vaccine should not be given to individuals in the following groups:
- Those with a history of severe allergic reaction to a previous polio vaccine dose.
- Those allergic to streptomycin, neomycin, or polymyxin B, which are components of the vaccine.
- If having fever or acute illness, vaccination should be postponed until recovery. Mild colds without fever are not a contraindication for vaccination.
Possible Side Effects After Receiving the Polio Vaccine
- Oral polio vaccine may cause symptoms similar to natural infection in about 1 in 1.5-2.2 million doses administered, with a 3,200-6,800 times higher risk in immunodeficient individuals.
- Injectable polio vaccine is safe and may cause mild pain at the injection site without severe reactions.
Note:
- There is no safety data available for the vaccine in pregnant or breastfeeding women.
