Polio-like paralysis in California

Enterovirus

Image credit: Jason Roberts

Recently a number of children in California have developed a poliomyelitis-like paralysis. The cause of this paralysis is not yet known, and information about the outbreak is scarce. Here is what we know so far:

  • At least 5, and perhaps as many as 20 children have suffered weakness or paralysis in one or more limbs. The median age of the patients is 12 years and the cases have been reported since 2012.
  • One group of 5 patients recently presented at the American Academy of Neurology Annual meeting developed full paralysis within 2 days, and have not recovered limb function in 6 months.
  • The cases are all located within a 100-mile radius.
  • A mild respiratory illness preceded paralysis in some of the children.
  • Enterovirus type 68 has been recovered from the stool of some of the patients.

I do not have any more information on this outbreak other than what I’ve obtained from ProMedMail. I have worked on enteroviruses, including poliovirus, for over 30 years, so I thought I might speculate on what might be transpiring.

What is a polio-like illness? Acute flaccid paralysis (AFP) is the term used to describe the sudden onset of weakness in limbs. AFP can have many etiologies, including viruses, bacteria, toxins, and systemic disease. It is used by the World Health Organization to maximize the ability to detect all cases of poliovirus. Confirmation that AFP is caused by poliovirus requires demonstration that the virus is present in the infected individual.

Is poliovirus the cause? I do not believe that poliovirus is causing the paralysis of children in California. I understand that they have all been immunized against poliovirus. In addition, should immunization have failed in any of these children, it seems unlikely that wild type polioviruses would be circulating in this area. Vaccine-derived polioviruses can cause paralysis but the US has not used this type of vaccine since 2000.

What might be causing the paralysis? AFP has both infectious and non-infectious etiologies. One possibility is that  a non-polio enterovirus is involved. Poliovirus is classified within the genus Enterovirus in the family Picornaviridae. Other enteroviruses besides poliovirus are known to cause paralytic disease, such as Coxsackieviruses, echoviruses, and many enteroviruses including types 70, 71, 89, 90, 91,96, 99, 102, and 114.

Most enterovirus infections can be associated with different clinical syndromes besides paralysis (such as respiratory disease), and therefore diagnosis is difficult. Stool is generally the most sensitive specimen for establishing an enterovirus infection. However, the virus may no longer be present at onset of symptoms. Polio is much easier to diagnose in individuals with AFP from whom virus can be identified: paralysis is the main serious symptom caused by infection. However note that 99 out of 100 poliovirus infections are asymptomatic or present with undifferentiated viral illness. The incidence of paralytic disease caused by other enteroviruses is even lower – for example 1 in 10,000 EV71 infections are paralytic. If all of the 20 California cases are caused by enteroviruses, this means that there have been many more infections without symptoms.

In one study of non-polio AFP in India, no virus could be isolated in 70% of the cases. Enterovirus 71 was the single most prevalent serotype associated with non-polio AFP. This virus currently causes large outbreaks of hand, foot, and mouth disease throughout Asia, with many fatalities and cases of acute flaccid paralysis. EV71 is known to circulate within the United States.

What about enterovirus 68? It has been reported that EV68 has been isolated from some of the paralyzed children. This isolation does not mean that the virus has caused the paralysis. Enterovirus infections of the respiratory and gastrointestinal tracts are very common and often do not result in any signs of disease. Random samplings of healthy individuals frequently demonstrate substantial rates of enterovirus infections.

Enterovirus type 68 was first isolated in California from an individual with respiratory illness. The virus is known to cause clusters of acute respiratory disease, and there is at least one report of its association with central nervous system disease. I believe it is an unlikely cause of the paralytic cases in California based solely on the past history of the virus and the fact that other enteroviruses are more likely to cause paralysis. It is not clear to me why enterovirus 68 would evolve to become substantially more neurotropic: entering the central nervous system is a dead end because the infection cannot be transmitted to a new host.

All of the above is pure speculation based on very little data. The paralysis might not even be caused by an infection. At this point a great deal of basic epidemiology needs to be done to solve the problem – if indeed it can be solved at all. Based on its population, California would be expected to have about 75 cases of acute flaccid paralysis each year of various etiologies, suggesting that the current number of cases is not unusual or unexpected.

Update: N. Gopal Raj wrote a story last year about acute flaccid paralysis in India, which has the highest rate of non-polio AFP in the world, with 60,000 cases reported in 2011.

India has been free of polio for three years

Poliovirus cutaway

Image credit: Jason Roberts

Three years ago today, on 13 January 2011, the last case of poliomyelitis was reported in India. This achievement represents a remarkable turnaround for a country where control of the disease had for years been extremely difficult. As recently as 2009 there were 741 confirmed cases of polio caused by wild-type virus in India. Being polio-free for three years is certainly a cause for celebration, but not for becoming complacent. Immunization efforts in India must not decline, because wild-type and vaccine-derived polioviruses continue to circulate and pose a threat to any unimmunized individual.

Wild polioviruses – those that have always been circulating in nature – continue to cause disease in Afghanistan and Pakistan, two countries close to India. Pakistan reported 58 polio cases in 2012, and 85 so far in 2013; for Afghanistan the numbers are 37 and 12. But distant countries can also transmit polio: recent outbreaks in the Horn of Africa and in Syria originated in Nigeria and Pakistan, respectively.

Perhaps a greater threat are vaccine-derived polioviruses. The Sabin poliovirus vaccines, which have so far been the mainstay of the polio eradication effort, comprise infectious viruses that are taken orally. Upon replication in the intestinal tract, the vaccine strains confer immunity to infection, but they also revert and become capable of causing paralysis. Such vaccine-derived polioviruses circulate and can cause outbreaks of polio. Because India has been using Sabin poliovirus vaccines intensely for many years, there is no doubt that vaccine-derived polioviruses are circulating in that country. If polio vaccine coverage drops, there will be outbreaks of polio caused by vaccine-derived strains. Even if wild polioviruses disappeared from the globe, as long as Sabin vaccines are used, vaccine-derived polioviruses will circulate. The solution to this conundrum is to switch to Salk’s inactivated poliovirus vaccine and wait for the Sabin-derived strains to disappear. This switch is now part of the WHO’s eradication plan (it wasn’t always), but it will not be easy: Salk vaccine must be injected, and therefore requires trained health care personnel; administering Sabin vaccine requires no special skills. But we cannot simply stop immunizing with Sabin vaccine – that is a recipe for outbreaks of polio.

According to the World Health Organization, being free of wild polio for three years means that the virus is probably no longer endemic in India. However, WHO does not certify individual countries as polio-free; rather it declares a WHO region polio-free when all countries in the Region have not reported a case of wild polio for 3 years in the face of highly active surveillance. The Americas, the Western Pacific, and European regions have been declared polio-free by WHO. India is part of the South-East Asia region, which also includes Bangladesh, Bhutan, Democratic People’s Republic of Korea, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, Thailand, and Timor-Leste, none of which have reported a case of polio for 3 years. WHO will decide in March whether to declare this region polio-free. That would leave the regions of Africa and the Eastern Mediterranean as the last known reservoirs of wild poliovirus.

Poliovirus silently (and not so silently) spreads

Poliovirus by Jason RobertsPoliovirus has been found in sewage in Israel. The virus detected is not vaccine-derived poliovirus; it is wild-type 1 poliovirus, the strain that occurs naturally in the wild and which the World Health Organization is trying very hard to eradicate from the planet.

As part of the global effort to eradicate poliovirus, environmental samples from many countries are routinely examined for the presence of the virus. Wild type poliovirus was detected in 30 sewage sample from 10 different sites, collected from 3 February to 30 June 2013 in Israel. No cases of paralytic disease have been detected in that country. This is not a surprising finding because only roughly one in 100 individuals infected with poliovirus develop paralysis.

During poliovirus infection, the virus replicates in the gastrointestinal tract and is shed in the feces. Most of the poliovirus-positive sewage samples were from southern Israel. Finding the virus at multiple sites suggests that the virus has been in the population for an extended period of time and that multiple individuals are shedding virus.

Why is wild type virus circulating in Israel? Poliovirus vaccine coverage in Israel is high but it is never 100%, and non-immunized individuals are hosts for the virus. Another explanation is related the the use of inactivated poliovirus vaccine (IPV) in Israel. Immunization with IPV, which is administered intramuscularly, does not protect the alimentary tract from infection. Therefore poliovirus can replicate in the intestine of immunized individuals, but once the virus reaches the blood its spread is blocked by anti-viral antibodies.

An interesting question is whether there is wild type poliovirus in the United States. I suspect that if we looked for poliovirus in our sewage, we would find it. However we no longer carry out surveillance of sewage for poliovirus and therefore we do not know if it is present.

Genetic analysis of wild type poliovirus from Israel suggests that it is related to the strain found in December 2012 in sewers in Cairo, Egypt. That virus in turn is closely related to virus from Pakistan, one of three countries from which wild type poliovirus has not been eradicated (the others are Nigeria and Afghanistan).

There is an ongoing outbreak of poliomyelitis in the Horn of Africa, with 65 cases in Somalia and 8 cases in Kenya. The virus causing that outbreak came from Nigeria. Somalia and Kenya had been free of polio since 2007 and 2011, respectively.

WHO has concluded that the risk of further international spread of wild type poliovirus from Israel as moderate to high. As long as there are individuals who are not immune, there will be a risk of poliovirus infection, in part due to the silent infections caused by the virus.

Deans write to Obama about CIA vaccine scheme in Pakistan

Deans of public health schools in the United States have sent the following letter to President Obama, in which they criticize the use of a vaccination campaign by the Central Intelligence Agency in Pakistan to hunt for Osama bin Laden. I wonder if he will reply.

January 6, 2013

Dear President Obama,

In the first years of the Peace Corps, its director, Sargent Shriver, discovered that the Central Intelligence Agency (CIA) was infiltrating his efforts and programs for covert purposes. Mr. Shriver forcefully expressed the unacceptability of this to the President. His action, and the repeated vigilance and actions of future directors, has preserved the Peace Corps as a vehicle of service for our country’s most idealistic citizens. It also protects our Peace Corps volunteers from unwarranted suspicion, and provides opportunities for the Peace Corps to operate in areas of great need that otherwise would be closed off to them.

In September Save the Children was forced by the Government of Pakistan (GoP) to withdraw all foreign national staff. This action was apparently the result of CIA having used the cover of a fictional vaccination campaign to gather information about the whereabouts of Osama Bin Laden. In fact, Save the Children never employed the Pakistani physician serving the CIA, yet in the eyes of the GoP he was associated with the organization. This past month, eight or more United Nations health workers who were vaccinating Pakistani children against polio were gunned down in unforgivable acts of terrorism. While political and security agendas may by necessity induce collateral damage, we as an open society set boundaries on these damages, and we believe this sham vaccination campaign exceeded those boundaries.

As an example of the gravity of the situation, today we are on the verge of completely eradicating polio. With your leadership, the U.S. is the largest bilateral donor to the Global Polio Eradication Initiative and has provided strong direction and technical assistance as well. Polio particularly threatens young children in the most disadvantaged communities and today has been isolated to just three countries: Afghanistan, Nigeria and Pakistan. Now, because of these assassinations of vaccination workers, the UN has been forced to suspend polio eradication efforts in Pakistan. This is only one example, and illustrates why, as a general principle, public health programs should not be used as cover for covert operations.

Independent of the Geneva Conventions of 1949, contaminating humanitarian and public health programs with covert activities threatens the present participants and future potential of much of what we undertake internationally to improve health and provide humanitarian assistance. As public health academic leaders, we hereby urge you to assure the public that this type of practice will not be repeated.

International public health work builds peace and is one of the most constructive means by which our past, present, and future public health students can pursue a life of fulfillment and service. Please do not allow that outlet of common good to be closed to them because of political and/or security interests that ignore the type of unintended negative public health impacts we are witnessing in Pakistan.

Sincerely,

Pierre M. Buekens, M.D., M.P.H., Ph.D.
Dean, Tulane University School of Public Health and Tropical Medicine*

James W. Curran, M.D., M.P.H.
Dean, Rollins School of Public Health, Emory University*

John R. Finnegan Jr., Ph.D.
Professor and Dean, University of Minnesota School of Public Health*
Chair of the Board, Association of Schools of Public Health*

Julio Frenk, M.D., M.P.H., Ph.D.
Dean and T&G Angelopoulos Professor of Public Health and International Development
Harvard School of Public Health*

Linda P. Fried, M.D., M.P.H.
Dean, Mailman School of Public Health, Columbia University*

Howard Frumkin, M.D., Dr.P.H.
Dean, School of Public Health, University of Washington*

Lynn R. Goldman, M.D., M.P.H.
Professor and Dean, School of Public Health and Health Services, George Washington University*

Jody Heymann, M.D., M.P.P., Ph.D.
Dean, UCLA Fielding School of Public Health*

Michael J. Klag, M.D., M.P.H.
Dean, Johns Hopkins Bloomberg School of Public Health*

Martin Philbert, Ph.D.
Dean, School of Public Health, University of Michigan*

Barbara K. Rimer, Dr.P.H.
Dean and Alumni Distinguished Professor
UNC Gillings School of Global Public Health*

Stephen M. Shortell, Ph.D.
Dean, School of Public Health, University of California Berkeley*

*Institutional affiliation is provided for identification only.

cc:
Regina M. Benjamin, United States Surgeon General
Hillary Rodham Clinton, Secretary of State
Thomas Frieden, Director, Centers for Disease Control and Prevention
Howard Koh, Assistant Secretary of Health
Michael J. Morell, Acting Director of the Central Intelligence Agency
Janet Napolitano, Secretary of Homeland Security
Kathleen Sibelius, Secretary of Health and Human Services

WHO will switch to type 2 inactivated poliovirus vaccine

Poliovirus by Jason RobertsThe World Health Organization’s campaign to eradicate poliomyelitis made impressive inroads in 2012: only 212 cases were reported, compared with 620 the previous year; moreover, India remained polio-free. The dark side of this story is that as wild polio is eliminated, vaccine-associated poliomyelitis moves in to take its place. The landmark decision by WHO to replace the infectious, type 2 Sabin poliovaccine with inactivated vaccine is an important step towards eliminating vaccine-associated polio.

A known side effect of the Sabin poliovirus vaccines, which are taken orally and replicate in the intestine, is vaccine-associated poliomyelitis. During the years that the Sabin poliovirus vaccines (also called oral poliovirus vaccine, or OPV) were used in the US, cases of poliomyelitis caused by vaccine-derived polioviruses (VDPV) occurred at a rate of about 1 per 1.4 million vaccine doses, or 7-8 per year. Once the disease was eradicated from the US in 1979, the only cases of polio were caused by VDPVs. For this reason the US switched to the Salk inactivated poliovirus vaccine (IPV) in 2000.

The main vaccine used by WHO in the global eradication effort has been a trivalent preparation comprising all three serotypes. When type 2 poliovirus was eradicated in 1999, many countries began immunizing only against types 1 and 3 poliovirus. As a consequence of this immunization strategy, population immunity to type 2 poliovirus declined. This switch, together with poor routine immunization coverage in some areas, has lead to polio outbreaks caused by cVDPV2 in countries such as Pakistan.

Alan Dove and I suggested in 1997 that it would be necessary to switch from OPV to IPV to achieve polio eradication. However, WHO did not agree with our position:

Dove and Racaniello believe that the reliance of the WHO on the live Sabin oral poliovirus vaccine (OPV) means that there will be a continuing threat of release of potentially pathogenic virus into the environment. They therefore recommend a switch to the inactivated polio vaccine (IPV). In response, Hull and Aylward explain why a switch from OPV is not necessary and describe the studies being sponsored by the WHO to determine how and when immunization can safely be ended.

I remember well the words of DA Henderson, the architect of smallpox eradication, when I proposed a switch to IPV at a conference in 2001:

There is no way it is going to come about and as an end-game strategy it is dreaming to believe that this is reasonable. So, it is just not on.

Apparently I was not dreaming: in May 2012 the 65th World Health Assembly requested that the Director-General “coordinate with all relevant partners, including vaccine manufacturers, to promote the research, production and supply of vaccines, in particular inactivated polio vaccines, in order to enhance their affordability, effectiveness and accessibility”. Later last year the Strategic Advisory Group of Experts on immunization (SAGE) called for a global switch from trivalent to bivalent OPV, eliminating the type 2 component. To ensure that circulating type 2 VDPVs do not pose a threat, SAGE also recommended that all countries introduce at least one dose of inactivated poliovaccine. This decision was announced in the 4 January 2013 Weekly Epidemiological Record (pdf).

The fact that WHO believes it is necessary to switch from type 2 OPV to IPV surely means that in the future, when types 1 and 3 polioviruses are eradicated, types 1 and 3 OPV will be replaced with IPV. This is the correct endgame strategy for eradicating polio. Once circulating VDPVs are no longer detectable on the planet – something that will probably not happen before 2020 – then we may safely stop immunization with IPV.

Poliovirus image courtesy of Jason Roberts.

Vaccine-associated poliomyelitis in Pakistan

Poliovirus by Jason RobertsAn outbreak of ten cases of poliomyelitis caused by circulating vaccine-derivied poliovirus type 2 (cVDPV2) is ongoing in Pakistan, centered in the Kila Abdulla/Pishin area of Baluchistan. The same virus strain has spread to the neighboring Kandahar province in Afghanistan, where two paralytic cases have been reported. Vaccine-derived poliomyelitis is a well-known consequence of immunization with the Sabin poliovirus vaccine.

There are three serotypes of poliovirus, each of which causes poliomyelitis. The three vaccine strains developed by Albert Sabin (OPV, oral poliovirus vaccine) contain mutations which prevent them from causing paralytic disease. When the vaccine is taken orally, the viruses replicate in the intestine, and immunity to infection develops. While replicating in the intestinal tract, the vaccine viruses undergo genetic changes. As a consequence, the OPV recipients excrete neurovirulent polioviruses. These so-called vaccine-derived polioviruses (VDPV) can cause poliomyelitis in the recipient of the vaccine or in a contact. During the years that the Sabin poliovirus vaccines were used in the US, cases of poliomyelitis caused by VDPV occurred at a rate of about 1 per 1.4 million vaccine doses, or 7-8 per year. Once the disease was eradicated from the US in 1979, the only cases of polio were caused by VDPVs. For this reason the US switched to the Salk (inactivated) poliovirus vaccine in 2000.

Because VDPVs are excreted in the feces, they can spread in communities. These circulating VDPVs, or cVDPVs, can cause outbreaks of poliomyelitis in under-immunized populations. Examples include outbreaks of poliomyelitis in an Amish community and in Nigeria in 2009 caused by cVDPV2. Nigeria employed trivalent OPV before 2003, the year that this country began a boycott of polio immunization. Because type 2 poliovirus had been eradicated from the globe in 1999, when immunization in Nigeria resumed in 2004, monovalent types 1 and 3 vaccine were used. The source of the VDPV type 2 in Nigeria was the trivalent vaccine used before 2003.

For many years the vaccine used by WHO in the global eradication effort was a trivalent preparation comprising all three serotypes. When type 2 poliovirus was eliminated, many countries began immunizing only against types 1 and 3 poliovirus. As a consequence of this immunization strategy, population immunity to type 2 poliovirus declined. This has likely lead to the emergence of cVDPV2 in Pakistan, together with poor routine immunization coverage.

The resurrection of poliovirus type 2 highlights the difficulties in eradicating a pathogen using a vaccine that can readily mutate to cause the disease that it is designed to prevent. As wild type polioviruses are eliminated, the only remaining polio will be caused by the vaccine. If immunization is then stopped, as planned by WHO, there will likely be outbreaks of polio caused by cVDPV of all three serotypes. The solution to this conundrum is to switch to the inactivated vaccine until cVDPVs disappear from the planet.

Exacerbating the polio situation in Pakistan was the murder in the past week of nine immunization workers in several provinces. The Taliban, which carried out the executions, accused them of being spies. This accusation originates from the CIA operation in 2011 in which a Pakistani doctor ran an immunization program in Abbottabad in an attempt to obtain DNA samples from the Bin Laden family. As a result of this violence, immunization campaigns in Balochistan have been suspended. Coupled with the previous refusal of many parents to have their children immunized, this action makes it likely that poliovirus will spread more extensively in the country, making eradication even more difficult.

Poliovirus image courtesy of Jason Roberts.

World Polio Day

Today, 24 October 2012, is World Polio Day:

World Polio Day (October 24) was established by Rotary International over a decade ago to commemorate the birth of Jonas Salk, who led the first team to develop a vaccine against poliomyelitis. Use of this inactivated poliovirus vaccine and subsequent widespread use of the oral poliovirus vaccine developed by Albert Sabin led to establishment of the Global Polio Eradication Initiative (GPEI) in 1988. Since then, GPEI has reduced polio worldwide by 99%.

The polio eradication effort has made huge inroads towards eliminating polio from the planet. In 1988 it was estimated that there were a total of 350,000 cases of poliomyelitis (probably an underestimate); as of this writing there have been 174 cases in 2012. India has been polio-free for over one year, a remarkable achievement. Only three countries have never seen a break in wild poliovirus transmission: Afghanistan, Nigeria, and Pakistan. Continued surveillance and extensive immunization efforts will be needed to remove the last pockets of the disease from these countries.

Because only 1% of poliovirus infections lead to paralytic disease, the 174 polio cases in 2012 translates to 17,400 infections. The virus clearly has the ability to circulate undetected, which can be a problem if surveillance drops. Another thorny issue is how to deal with immunization once the disease has been eradicated. The vaccine strains used for immunization revert to virulence during replication in the human intestine, with the consequence that immunized individuals shed virulent poliovirus into the environment. These viruses will pose a threat to non-immune individuals. How long these vaccine-derived neurovirulent strains will persist in the population is unknown. Therefore we cannot simply stop vaccinating against polio once the disease is eradicated. It will likely be necessary to immunize globally with the non-infectious inactivated poliovirus vaccine until vaccine derived polioviruses are no longer detected.

Related: World Polio Day

India polio-free for one year

Year in polio 2011A year has passed since the last reported case of poliomyelitis in India, which occurred on 13 January 2011 in a two year old girl in Howrah, West Bengal. If no additional cases are reported in the next few weeks (some samples are currently being tested for the virus), then it will mark the first time that India has been polio free for one year.

This achievement represents a remarkable turnaround for India, where control of the disease had for years been extremely difficult. As recently as 2009 there were 741 confirmed cases of polio caused by wild-type virus (as opposed to vaccine-derived virus) in India. The tide turned in 2010 with only 42 confirmed polio cases, and in calendar year 2011 there was just one. That is why the 2011 map marking locations of confirmed wild polio cases in India (see figure) shows only one red dot (paralysis caused by type 1 poliovirus) in the country. The blue dots indicate cases caused by type 3 poliovirus.

The challenge now is to keep India free of polio. The map shows why this will be difficult – there are many red dots (cases of type 1 polio) in neighboring Pakistan and Afghanistan. Poliovirus does not respect national borders – China had been free of polio since 1999, but now there are red dots in that country. That outbreak was imported from Pakistan. Even the polio cases in more distant countries such as Africa constitute a threat. As long as there is polio somewhere, all countries must maintain extensive immunization programs. Whether or not that will happen depends upon money, determination, and allowing immunization campaigns to proceed without interruption.

Once polio was eradicated from the United States, the only poliomyelitis was caused by the Sabin vaccine. Consequently this country switched to the use of inactivated vaccine in 2000. As other countries eliminate the disease, vaccine-associated poliomyelitis will become more prominent. If eradication of polio is achieved, the world will have to switch to using inactivated poliovaccine.

Related:

Wild poliovirus in China
Dreaming of inactivated poliovaccine
Poliomyelitis after a twelve year incubation period
Poliovirus vaccine litigation

 

Wild poliovirus in China

The World Health Organization has confirmed that cases of poliomyelitis in China were caused by wild poliovirus type 1:

1 SEPTEMBER 2011 – The Ministry of Health, China, has informed WHO that wild poliovirus type 1 (WPV1) has been isolated from four young children, aged between four months and two years, with onset of paralysis between 3 and 27 July 2011. All four cases are from Hetian prefecture, Xinjiang Uygur autonomous region, China. Genetic sequencing of the isolated viruses indicates they are genetically-related to viruses currently circulating in Pakistan. The last WPV case in China was reported in 1999, due to an importation from India. The last indigenous polio case occurred in China in 1994.

Remember that only one in 100 poliovirus infections lead to paralysis. For the four paralytic cases reported in China, there are likely 400 individuals who were infected with the virus but did not display obvious symptoms. This suggests a lapse in immunization coverage in this region. Consequently a polio vaccination campaign is planned for early September, the target being 3.8 million children <15 years of age in the outbreak area.

Pakistan, which shares a border with Hetian prefecture, appears to be the origin of the poliovirus strain causing the outbreak. Wild poliovirus type 1 continues to circulate in Pakistan, causing 76 reported cases of paralytic disease so far this year. This incident emphasizes the need for continued high immunization coverage in all countries until eradication of the virus is achieved. It is estimated that China has achieved >99.5% coverage for the third dose of poliovirus vaccine. In a country of 1.3 billion people, that leaves a large number of susceptible individuals.

TWiV #79: Red hot chili viruses

Hosts: Vincent Racaniello and Alan Dove.

On episode #79 of the podcast “This Week in Virology”, Vincent and Alan converse about making published science accessible to everyone, global eradication of poliomyelitis, and whether a plant virus can cause disease in humans.

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