Q&A on Poliomyelitis
What is polio?
- Poliomyelitis (polio) is a highly infectious disease caused by the wild poliovirus. It invades the nervous system, and can cause paralysis or even death in a matter of hours.
How is polio transmitted?
- Polio enters the body through the mouth, in water or food that has been contaminated with faecal material from an infected person. The virus multiplies in the intestine and is excreted by the infected person in faeces, which can pass the virus to others.
What are the symptoms of polio?
- Initial symptoms of polio are: fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs.
Who is at risk of polio?
- Polio mainly affects children under the age of 5 years.
What are the effects of polio?
One in every 200 cases of persons infected with polio leads to irreversible paralysis (usually in the legs).
Among those paralyzed, 5%-10% die when their breathing muscles are immobilized by the virus.
Is there a cure for polio?
- No, there is no cure for polio, but the disease can only be prevented by immunization. Before the use of vaccine, polio was the most common cause of permanent disability.
What kinds of vaccines are available for prevention of poliomyelitis?
- Two safe and effective vaccines exist – the oral polio vaccine (OPV), which is given by mouth and inactivated polio vaccine (IPV) which is injected. These vaccines are essential protection for children against polio. Given multiple times, the vaccine protects a child for life.
How effective is OPV?
- Oral polio vaccine contains attenuated (weakened) polio virus. It is given by mouth. In order to develop immunity to polio, several doses of vaccine are needed. OPV has been successfully used to eliminate polio in most countries of the world, including China. Over the past 10 years, more than 10 billion doses of OPV have been given throughout the world, preventing an estimated 3.5 million cases of polio during that time.
Is it safe to administer multiple doses of OPV to children?
- Yes, it is safe. It is very important to administer multiple doses of polio vaccine to children. The vaccine is designed to be administered multiple times to ensure full protection. This vaccine is safe for all children. Each additional dose further strengthens a child’s immunity level against polio.
Does OPV have any side-effects?
- OPV is a very safe vaccine. However, in approximately one in every 3 million people vaccinated with OPV will develop Vaccine Associated Paralytic Polio (VAPP). In this very rare circumstance, OPV causes paralysis.
How many doses of OPV does a child need before being protected?
- The number of doses it takes to immunize a child depends entirely on the child’s health and nutritional status, and how many other viruses that child has been exposed to. Until a child is fully immunized, he or she is still at risk from polio.
What is the status of OPV in China?
- OPV was first made in China in 1959. Large-scale OPV vaccination started in the 1960s, and vaccination expanded to the whole country in the 1970s. By 1982, OPV was integrated into the standard vaccine schedule. Since the late 1990s, approximately 2-3 billion doses of OPV have been used annually in China. China produces enough OPV to vaccinate all children born in the country every year.
How effective is IPV?
- IPV is a highly effective and safe vaccine. Inactivated polio vaccine (IPV) does not contain live virus. Instead, it contains microscopic pieces of the virus that have been completely neutralized (killed). IPV is given by injection, and in order to develop immunity to polio, several doses of vaccine are also needed.
What is the status of IPV in China?
- At present, no IPV is produced in China. Imported IPV became available in September 2009, but the supply is limited and the vaccine is expensive and has to be paid out of pocket by the recipient.
Does IPV have any side-effects?
- IPV does not cause VAPP. However, IPV induces only very low levels of immunity in the intestine. As a result, when a person immunized with IPV is infected with wild poliovirus, the virus can still multiply inside the intestines and be shed in the faeces, risking continued circulation of the virus in a community.
What is the WHO recommendation regarding the use of OPV or IPV vaccines?
- The different polio vaccines have different strengths and weaknesses. Although OPV is safe and effective, in extremely rare cases the live attenuated vaccine virus in OPV can cause paralysis. The occurrence of VAPP has been estimated at 2-4 cases/1,000,000 birth cohort per year in countries using OPV.
- Vaccine-associated paralytic polio (VAPP) is much more common among individuals with an immune deficiency. IPV is not associated with VAPP, however IPV induces only very low levels of immunity in the intestine. As a result, when a person immunized with IPV is infected with wild poliovirus, the virus can still multiply inside the intestines and be shed in the faeces, risking continued circulation of the virus in a given community.
- At a time when wild poliovirus is still present in several countries and the risk of importation into polio-free areas such as China exists, WHO continues to recommend that countries with middle or lower incomes provide OPV. Because OPV is a live virus vaccine that is shed by vaccinated individuals, it can spread to contacts of the vaccinated person, and, therefore, immunize additional people against polio. OPV is less costly, easier to administer, and is the vaccine of choice when wild poliovirus is imported.
- Wild poliovirus is still circulating in China's neighbouring countries of Pakistan and Afghanistan. For this reason, maintaining high population coverage with vaccine is extremely important.
What is the policy for use of OPV vaccines?
- The Ministry of Health is closely following developments for domestic IPV production. It regularly receives updates on WHO recommendations for polio vaccine use. However, the final decision as to which type of polio vaccine is given to children is made by the Government, taking many factors into account. Currently, the Ministry of Health continues to recommend the use of OPV in its national immunization programme.