Polio vaccines are vaccines used to prevent poliomyelitis (polio). There are two types: one that uses inactivated poliovirus and is given by injection (IPV), and one that uses weakened poliovirus and is given by mouth (OPV). The World Health Organization recommends all children be fully vaccinated against polio. The two vaccines have eliminated polio from most of the world, and reduced the number of cases each year from an estimated 350,000 in 1988 to 37 in 2016.
The inactivated polio vaccines are very safe. Mild redness or pain may occur at the site of injection. Oral polio vaccines result in vaccine-associated paralytic poliomyelitis in about three per million doses. This compares with one in two hundred who are paralysed following a polio infection. Both are generally safe to give during pregnancy and in those who have HIV/AIDS but are otherwise well.
The first polio vaccine was the inactivated polio vaccine. It was developed by Jonas Salk and came into use in 1955. The oral polio vaccine was developed by Albert Sabin and came into commercial use in 1961. They are on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost in the developing world is about US$0.25 per dose for the oral form as of 2014. In the United States it costs between $25â€"50 for the inactivated form.
Medical uses
Interruption of person-to-person transmission of the virus by vaccination is important in the global polio eradication, since there is no long term carrier state for poliovirus in individuals with normal immune function, polio viruses have no non-primate reservoir in nature, and survival of the virus in the environment for an extended period of time appears to be remote.
Inactivated
When the current formulation of IPV is used, 90% or more of individuals develop protective antibody to all three serotypes of polio virus after two doses of inactivated polio vaccine (IPV), and at least 99% are immune to polio virus following three doses. The duration of immunity induced by IPV is not known with certainty, although a complete series is thought to provide protection for many years.
Attenuated
OPV also proved to be superior in administration, eliminating the need for sterile syringes and making the vaccine more suitable for mass vaccination campaigns. OPV also provided longer lasting immunity than the Salk vaccine as it provides both humoral immunity and cell-mediated immunity.
One dose of OPV produces immunity to all three poliovirus serotypes in approximately 50% of recipients. Three doses of live-attenuated OPV produce protective antibodies to all three poliovirus types in more than 95% of recipients. OPV produces excellent immunity in the intestine, the primary site of wild poliovirus entry, which helps prevent infection with wild virus in areas where the virus is endemic. The live virus used in the vaccine is shed in the stool and can be spread to others within a community. The live virus also has stringent requirements for transport and storage, which are a problem in some hot or remote areas. As with other live-virus vaccines, immunity initiated by OPV is probably lifelong.
The trivalent (against wild type 1, 2 and 3) OPV has been used to nearly eradicated polio infection worldwide. Lead by The Global Polio Eradication Initiative, 155 countries switched to use the bivalent (against wild type 1 and 3) between 17 April and 1 May 2016. The bivalent OPV is at more effective against type 1 and 3 but does not cover type 2. The United States as of 2017 continues to recommend the use of a trivalent version, but a fully inactivated version.
Schedule
The World Health Organization recommends three or four doses starting at two months of age. It can be begun earlier but then additional doses are needed.
Side effects
The inactivated polio vaccines are very safe. Mild redness or pain may occur at the site of injection. Oral polio vaccine results in vaccine-associated paralytic poliomyelitis in about three per million doses. They are generally safe to give during pregnancy and in those who have HIV/AIDS but are otherwise well.
Vaccine-induced polio
A potential, but rare, adverse effect of the oral polio vaccine (OPV) is its known ability to recombine to a form that may cause neurological infection and cause paralysis. Clinical disease, including paralysis, caused by vaccine-derived poliovirus (VDPV) is indistinguishable from that caused by wild polioviruses. This is believed to be a rare event, but outbreaks of vaccine-associated paralytic poliomyelitis (VAPP), caused by a circulating vaccine-derived poliovirus (cVDPV), have been reported, and tend to occur in areas of low coverage by OPV, presumably because the OPV is itself protective against the related outbreak strain.
Contamination concerns
In 1960, it was determined that the rhesus monkey kidney cells used to prepare the poliovirus vaccines were infected with the SV40 virus (Simian Virus-40). SV40 was also discovered in 1960 and is a naturally occurring virus that infects monkeys. In 1961, SV40 was found to cause tumors in rodents. More recently, the virus was found in certain forms of cancer in humans, for instance brain and bone tumors, pleural and peritoneal mesothelioma, and some types of non-Hodgkin's lymphoma. However, it has not been determined that SV40 causes these cancers.
SV40 was found to be present in stocks of the injected form of the polio vaccine (IPV) in use between 1955 and 1963. It is not found in the OPV form. Over 98 million Americans received one or more doses of polio vaccine between 1955 and 1963 when a proportion of vaccine was contaminated with SV40; it has been estimated that 10â€"30 million Americans may have received a dose of vaccine contaminated with SV40. Later analysis suggested that vaccines produced by the former Soviet bloc countries until 1980, and used in the USSR, China, Japan, and several African countries, may have been contaminated; meaning hundreds of millions more may have been exposed to SV40.
In 1998, the National Cancer Institute undertook a large study, using cancer case information from the Institute's SEER database. The published findings from the study revealed that there was no increased incidence of cancer in persons who may have received vaccine containing SV40. Another large study in Sweden examined cancer rates of 700,000 individuals who had received potentially contaminated polio vaccine as late as 1957; the study again revealed no increased cancer incidence between persons who received polio vaccines containing SV40 and those who did not. The question of whether SV40 causes cancer in humans remains controversial however, and the development of improved assays for detection of SV40 in human tissues will be needed to resolve the controversy.
During the race to develop an oral polio vaccine several large scale human trials were undertaken. By 1958, the National Institutes of Health had determined that OPV produced using the Sabin strains were the safest. Between 1957 and 1960, however, Hilary Koprowski continued to administer his vaccine around the world. In Africa, the vaccines were administered to roughly one million people in the Belgian territories (now the Democratic Republic of the Congo, Rwanda and Burundi). The results of these human trials have been controversial, and unfounded accusations in the 1990s arose that the vaccine had created the conditions necessary for transmission of SIV from chimpanzees to humans, causing HIV/AIDS. These hypotheses have, however, have been conclusively refuted. By 2004, cases of poliomyelitis in Africa had been reduced to just a small number of isolated regions in the western portion of the continent, with sporadic cases elsewhere. Recent local opposition to vaccination campaigns have evolved due to lack of adequate information, often relating to fears that the vaccine might induce sterility. The disease has since resurged in Nigeria and in several other African nations without necessary information, which epidemiologists believe is due to refusals by certain local populations to allow their children to receive the polio vaccine.
Manufacture
Inactivated
The Salk vaccine, or inactivated poliovirus vaccine (IPV), is based on three wild, virulent reference strains, Mahoney (type 1 poliovirus), MEF-1 (type 2 poliovirus), and Saukett (type 3 poliovirus), grown in a type of monkey kidney tissue culture (Vero cell line), which are then inactivated with formalin. The injected Salk vaccine confers IgG-mediated immunity in the bloodstream, which prevents polio infection from progressing to viremia and protects the motor neurons, thus eliminating the risk of bulbar polio and post-polio syndrome.
In the United States, vaccine is administered along with the tetanus, diphtheria, and acellular pertussis vaccines (DTaP) and a pediatric dose of hepatitis B vaccine. In the UK, IPV is combined with tetanus, diphtheria, pertussis, and Haemophilus influenzae type b vaccines.
Attenuated
Oral polio vaccine (OPV) is an attenuated vaccine, produced by the passage of the virus through non-human cells at a sub-physiological temperature, which produces spontaneous mutations in the viral genome. Oral polio vaccines were developed by several groups, one of which was led by Albert Sabin. Other groups, led by Hilary Koprowski and H.R. Cox, developed their own attenuated vaccine strains. In 1958, the National Institutes of Health created a special committee on live polio vaccines. The various vaccines were carefully evaluated for their ability to induce immunity to polio, while retaining a low incidence of neuropathogenicity in monkeys. Large-scale clinical trials performed in the Soviet Union in late 1950s to early 1960s by Mikhail Chumakov and his colleagues demonstrated safety and high efficacy of the vaccine. Based on these results, the Sabin strains were chosen for worldwide distribution. There are 57 nucleotide substitutions which distinguish the attenuated Sabin 1 strain from its virulent parent (the Mahoney serotype), two nucleotide substitutions attenuate the Sabin 2 strain, and 10 substitutions are involved in attenuating the Sabin 3 strain. The primary attenuating factor common to all three Sabin vaccines is a mutation located in the virus's internal ribosome entry site (IRES) which alters stem-loop structures, and reduces the ability of poliovirus to translate its RNA template within the host cell. The attenuated poliovirus in the Sabin vaccine replicates very efficiently in the gut, the primary site of infection and replication, but is unable to replicate efficiently within nervous system tissue. In 1961, type 1 and 2 monovalent oral poliovirus vaccine (MOPV) was licensed, and in 1962, type 3 MOPV was licensed. In 1963, trivalent OPV (TOPV) was licensed, and became the vaccine of choice in the United States and most other countries of the world, largely replacing the inactivated polio vaccine. A second wave of mass immunizations led to a further dramatic decline in the number of polio cases. Between 1962 and 1965 about 100 million Americans (roughly 56% of the population at that time) received the Sabin vaccine. The result was a substantial reduction in the number of poliomyelitis cases, even from the much reduced levels following the introduction of the Salk vaccine.
OPV is usually provided in vials containing 10â€"20 doses of vaccine. A single dose of oral polio vaccine (usually two drops) contains 1,000,000 infectious units of Sabin 1 (effective against PV1), 100,000 infectious units of the Sabin 2 strain, and 600,000 infectious units of Sabin 3. The vaccine contains small traces of antibioticsâ€"neomycin and streptomycinâ€"but does not contain preservatives.
History
In generic sense, vaccination works by priming the immune system with an 'immunogen'. Stimulating immune response, via use of an infectious agent, is known as immunization. The development of immunity to polio efficiently blocks person-to-person transmission of wild poliovirus, thereby protecting both individual vaccine recipients and the wider community.
The development of two polio vaccines led to the first modern mass inoculations. The last cases of paralytic poliomyelitis caused by endemic transmission of wild virus in the United States occurred in 1979, with an outbreak among the Amish in several Midwest states.
1935
This year, two separate teams were at work developing and testing a polio vaccine. Both projects came to disastrous ends. At New York University, Maurice Brodie, MD (1903â€"1939), a young researcher, prepared a killed poliovirus vaccine, testing it on chimpanzees, on himself, and finally on children. He enrolled about 11,000 individuals (in both control and vaccine groups) in his trial. Meanwhile, John Kolmer, MD, of Temple University in Philadelphia developed an attenuated poliovirus vaccine, which he tested in about 10,000 children. The tests proved a disaster. Several subjects died of polio, and many were paralyzed, made ill, or suffered allergic reactions to the vaccines.
1936
In 1936, Maurice Brodie, a research assistant at New York University, attempted to produce a formaldehyde-killed polio vaccine from ground-up monkey spinal cords. His initial attempts were hampered by the difficulty of obtaining enough virus. Brodie first tested the vaccine on himself and several of his assistants. He then gave the vaccine to three thousand children. Many of these children developed allergic reactions, but none developed immunity to polio. Philadelphia pathologist John Kolmer also claimed to have developed a vaccine that same year, but it too produced no immunity and was blamed for causing cases of paralytic polio, nine of them fatal.
1948
A breakthrough came in 1948 when a research group headed by John Enders at the Children's Hospital Boston successfully cultivated the poliovirus in human tissue in the laboratory. This group had recently successfully grown mumps in cell culture. In March 1948 Thomas H. Weller was attempting to grow varicella virus in embryonic lung tissue. He had inoculated the planned number of tubes when he noticed that there were a few unused tubes. He retrieved a sample of mouse brain infected with polio virus and added it to the remaining test tubes, on the off chance that the virus might grow. The varicella cultures failed to grow but the polio cultures were successful. This development greatly facilitated vaccine research and ultimately allowed for the development of vaccines against polio. Enders and his colleagues, Thomas H. Weller and Frederick C. Robbins, were recognized in 1954 for their labors with a Nobel Prize in Physiology or Medicine. Other important advances that led to the development of polio vaccines were: the identification of three poliovirus serotypes (Poliovirus type 1 â€" PV1, or Mahoney; PV2, Lansing; and PV3, Leon); the finding that prior to paralysis, the virus must be present in the blood; and the demonstration that administration of antibodies in the form of gamma globulin protects against paralytic polio.
1950â€"1955
The U.S. experienced an outbreak of 58,000 and 35,000 polio cases, respectively, up from a typical number of some 20,000 a year. Amid this U.S. polio epidemic, millions of dollars were invested in finding and marketing a polio vaccine by commercial interests, including Lederle Laboratories in New York under the direction of H. R. Cox. Also working at Lederle was Polish-born virologist and immunologist Hilary Koprowski of the Wistar Institute in Philadelphia, who tested the first successful polio vaccine, in 1950. His vaccine, however, being a live attenuated virus taken orally, was still in the research stage and would not be ready for use until five years after Jonas Salk's polio vaccine (a dead-virus injectable vaccine) had reached the market. Koprowski's attenuated vaccine was prepared by successive passages through the brains of Swiss albino mice. By the seventh passage, the vaccine strains could no longer infect nervous tissue or cause paralysis. After one to three further passages on rats, the vaccine was deemed safe for human use. On 27 February 1950, Koprowski's live, attenuated vaccine was tested for the first time on an 8-year-old boy living at Letchworth Village, an institution for the physically and mentally disabled located in New York. After the child suffered no side effects, Koprowski enlarged his experiment to include 19 other children.
Jonas Salk
The first effective polio vaccine was developed in 1952 by Jonas Salk and a team at the University of Pittsburgh that included Julius Youngner, Byron Bennett, L. James Lewis, and Lorraine Friedman, which required years of subsequent testing. Salk went on CBS radio to report a successful test on a small group of adults and children on 26 March 1953; two days later the results were published in JAMA. Beginning 23 February 1954, the vaccine was tested at Arsenal Elementary School and the Watson Home for Children in Pittsburgh, Pennsylvania.
Salk's vaccine was then used in a test called the Francis Field Trial, led by Thomas Francis, the largest medical experiment in history at that time. The test began with approximately 4,000 children at Franklin Sherman Elementary School in McLean, Virginia, and would eventually involve 1.8 million children, in 44 states from Maine to California. By the conclusion of the study, roughly 440,000 received one or more injections of the vaccine, about 210,000 children received a placebo, consisting of harmless culture media, and 1.2 million children received no vaccination and served as a control group, who would then be observed to see if any contracted polio.
The results of the field trial were announced 12 April 1955 (the tenth anniversary of the death of President Franklin D. Roosevelt, whose paralysis was generally believed to have been caused by polio). The Salk vaccine had been 60â€"70% effective against PV1 (poliovirus type 1), over 90% effective against PV2 and PV3, and 94% effective against the development of bulbar polio. Soon after Salk's vaccine was licensed in 1955, children's vaccination campaigns were launched. In the U.S, following a mass immunization campaign promoted by the March of Dimes, the annual number of polio cases fell from 35,000 in 1953 to 5,600 by 1957. By 1961 only 161 cases were recorded in the United States.
A week earlier in April 1955, Pierre Lépine at the Pasteur Institute in Paris also announced an effective polio vaccine.
1961
At the same time that Salk was testing his vaccine, both Albert Sabin and Hilary Koprowski continued working on developing a vaccine using live virus. During a meeting in Stockholm to discuss polio vaccines in November 1955, Sabin presented results obtained on a group of 80 volunteers, while Koprowski read a paper detailing the findings of a trial enrolling 150 people. Sabin and Koprowski both eventually succeeded in developing vaccines. Because of the commitment to the Salk vaccine in America, Sabin and Koprowski both did their testing outside of the United States, Sabin in Mexico and then in the Soviet Union, and Koprowski in the Congo and Poland. In 1957, Sabin developed a trivalent vaccine, containing attenuated strains of all three types of poliovirus. In 1959, ten million children in the Soviet Union received the Sabin oral vaccine. For this work, Sabin was given the medal of the Order of Friendship Among Peoples, described as the Soviets' highest civilian honor, despite having become an American during the height of the cold war. Sabin's oral vaccine using live virus came into commercial use in 1961. Once Sabin’s oral vaccine became widely available, it supplanted Salk’s injected vaccine because it was cheaper to produce and easier to administer.
1987
An enhanced-potency IPV (inactivated polio vaccine) was licensed in the United States in November 1987, and is currently the vaccine of choice in the United States. The first dose of polio vaccine is given shortly after birth, usually between 1 and 2 months of age, a second dose is given at 4 months of age. The timing of the third dose depends on the vaccine formulation but should be given between 6 and 18 months of age. A booster vaccination is given at 4 to 6 years of age, for a total of four doses at or before school entry. In some countries, a fifth vaccination is given during adolescence. Routine vaccination of adults (18 years of age and older) in developed countries is neither necessary nor recommended because most adults are already immune and have a very small risk of exposure to wild poliovirus in their home countries. In 2002, a pentavalent (five-component) combination vaccine (called Pediarix) containing IPV was approved for use in the United States.
1988
A global effort to eradicate polio, led by the World Health Organization, UNICEF, and The Rotary Foundation, began in 1988 and has relied largely on the oral polio vaccine developed by Albert Sabin and Mikhail Chumakov (Sabin-Chumakov vaccine).
Post-1990
Polio was eliminated in the Americas by 1994. The disease was officially eliminated in 36 Western Pacific countries, including China and Australia in 2000. Europe was declared polio-free in 2002. Since January 2011, there were no reported cases of the disease in India, and hence in February 2012, the country was taken off the WHO list of polio endemic countries. In March 2014, India was declared a polio-free country.
Although poliovirus transmission has been interrupted in much of the world, transmission of wild poliovirus does continue and creates an ongoing risk for the importation of wild poliovirus into previously polio-free regions. If importations of poliovirus occur, outbreaks of poliomyelitis may develop, especially in areas with low vaccination coverage and poor sanitation. As a result, high levels of vaccination coverage must be maintained. In November 2013, the World Health Organization announced a polio outbreak in Syria. In response, the Armenian government put out a notice asking Syrian Armenians under age 15 to get the polio vaccine. As of 2014, polio virus has spread out to ten countries mainly in Africa, Asia and the Middle East with Pakistan, Syria and Cameroon advising vaccinations to outbound travelers.
Polio vaccination programs have received resistance from some people in Pakistan, Afghanistan, and Nigeria (the three countries with remaining polio cases). There is distrust surrounding vaccines in Pakistan as in 2011 the CIA organized a fake vaccination program in order to help find Osama Bin Laden. Additionally, some people believe that the vaccines are secretly being used for sterilization of Muslims. In 2015, the World Health Organization announced a deal with the Taliban to encourage them to distribute the vaccine in areas they control. However, on September 11, 2016, two unidentified gunmen associated with the Pakistani Taliban, Jamaat-ul-Ahrar, shot Zakaullah Khan, a doctor who was administering polio vaccines in Pakistan. The leader of the Jamaat-ul-Ahrar claimed responsibility for the shooting and says that the group will continue to keep doing these kinds of attacks. This resistance to and skepticism of vaccinations has consequently slowed down the polio eradication process within the three remaining countries.
Society and culture
Cost
The wholesale cost is about US$0.25 per dose for the oral form as of 2014. The Global Alliance for Vaccines and Immunization (GAVI) supplies the inactivated vaccine to developing countries for as little as €0.75 (about US$1) per dose in ten-dose vials. In the United States, the inactivated form costs between $25â€"50.
Misconceptions
A widespread misconception has arisen in Pakistan that polio vaccine contained Haram ingredients and could cause impotence and infertility in male children, leading some less-educated parents not to have their children vaccinated. This belief is most prevalent in the Khyber Pakhtunkhwa province and the FATA region, where people are likely to be influenced by conservative teachings. There also have been attacks on polio vaccination teams. This is hampering international efforts to eradicate polio in Pakistan and globally since the virus can be carried by travelers.
See also
- Cold war tensions and the polio vaccine
- Poliomyelitis eradication
References
External links
- Global Polio Eradication Initiative final project to eliminate polio by 2018.
- History of Vaccines Website â€" History of Polio History of Vaccines, a project of the College of Physicians of Philadelphia
- PBS.org â€" 'People and Discoveries: Salk Produces Polio Vaccine 1952', PBS
- Conquering Polio, Smithsonian Magazine, April 2005
- The Global Effort To Eradicate Polio, Dream 2047 Magazine, April 2004
