The Wall of Polio, version 3.0

Wall of Polio 3.0Back in 2013 I built a Wall of Polio in my laboratory – a large stack of six-well cell culture plates that have been used to measure the concentration of polioviruses in various samples by plaque assay. It became a focal point of the lab at which many guests came to have their photographs taken. Sadly, the Wall fell twice. Now a new Wall – version 3.0 – has been completed.

The new Wall of Polio is in my office at Columbia University Medical Center, where it will not annoy the Fire Inspector (the former Wall partially blocked an aisle). Furthemore, the new Wall is glued together, so it will not come apart. Its construction is documented in the photographs below. The Wall of Polio 3.0 is built with 1,464 six-well plates of HeLa cells that were used to determine the titer of poliovirus. We have also already had a number of visitors to Wall 3.0.

Because the Wall is impressive, it attracts attention, which can then be used to explain the plaque assay and determining virus titer. Therefore it is simply another tool that I used to teach the world about virology.

When you visit, expect that I will ask to photograph you before the Wall. Only a few have refused.


TWiV 331: Why is this outbreak different from all other outbreaks?

On episode #331 of the science show This Week in Virology, the TWiV team discusses the possible association of the respiratory pathogen enterovirus D68 with neurological disease.

You can find TWiV #331 at

Covering up a naked virus

Sabin type 2 poliovirusViruses can be broadly classified according to whether or not the particle is enveloped – surrounded by a membrane taken from the host cell – or naked. Some naked viruses apparently are more modest than we believed.

Members of the family Picornaviridae, which include Hepatitis A virus, poliovirus, and Coxsackieviruses, have non-enveloped particles that consist of a protein shell surrounding the viral RNA genome (poliovirus is illustrated). Examples of viruses that are enveloped include dengue virus, influenza virus, and measles virus.

Recently it was discovered that hepatitis A virus (HAV) particles are released from cells in membrane vesicles containing 1-4 virus particles. These membranous structures resemble exosomes, which are also released from uninfected cells and play roles in various biological processes. Enveloped hepatitis A virus particles are present in the blood of infected humans. However virus in the feces, which is transmitted to other hosts, is not enveloped.

Viral envelopes typically contain viral glycoproteins, such as the HA protein of influenza viruses, which serve important functions during replication, such as attachment to cell receptors. Envelope glycoproteins are also the target of antibodies that block viral infection. The presence of an envelope makes HAV resistant to neutralization with antibodies, because the membrane contains no viral proteins that can be blocked by antibodies.

Two other non-enveloped picornaviruses, Coxsackievirus B and poliovirus, are also released from cells within membrane vesicles. These virus particles are in vesicles derived from the autophagy pathway, which captures and recycles cytoplasmic contents by ejecting them from the cell.

What is the function of the membrane acquired by these naked viruses? Perhaps immune evasion: the presence of the cell membrane makes HAV and Coxsackievirus B virus particles resistant to neutralization with antibody. The ability to deliver multiple virus particles to a single cell might help to overcome genetic defects in the viral genome that are a consequence of the high mutation rates of these viruses.

An interesting problem is how these cloaked viruses enter cells, because there is no evidence that the membranes contain any viral proteins that could interact with a cell receptor. Nevertheless, entry of enveloped HAV and poliovirus into cells requires the known viral receptor. Perhaps the vesicles are taken into the cell by endocytosis, where viral particles are released from the vesicles, and then bind receptors to initiate escape of the genome.

Should HAV, poliovirus, and Coxsackievirus B be reclassified as enveloped viruses? Probably not, in part because the membranes surrounding these virus particles are not needed for infectivity. In contrast, removal of the membrane from influenza virus, dengue virus, or measles virus destroys their infectivity. Enveloped viruses acquire a membrane after the internal components have been assembled, whether they are helical or icosahedral nucleocapsids. In contrast, HAV, poliovirus, and Coxsackievirus B become fully infectious particles before they acquire an envelope.

Another argument against calling picornaviruses enveloped is that viral membranes contain viral glycoproteins that allow attachment to cell receptors and release of the viral genome into the cell. There is no evidence that the membranes of picornaviruses contain viral proteins.

The acquisition of a membrane may have taken place later in the evolution of picornaviruses, to allow more efficient infection or evasion of host responses. Alternatively, the membrane may simply be a by-product acquired when these viruses exit the cell by a non-lytic mechanism.

While the finding of membranes around picornavirus particles is intriguing, I am not yet convinced that these viruses should be considered to be enveloped. I would like to know if other non-enveloped viruses are similarly released from cells in membranous cloaks, and the function of this addition for viral replication in the host.

TWiV 328: Lariat tricks in 3D

On episode #328 of the science show This Week in Virology, the TWiVocateurs discuss how the RNA polymerase of enteroviruses binds a component of the splicing machinery and inhibits mRNA processing.

You can find TWiV #328 at

Viral supercomputer simulations

Jason Roberts, a virologist at the Victorian Infectious Disease Reference Laboratory in Melbourne, Australia, creates three-dimensional simulations of viruses showing how the molecules that make up the capsid and genome might move in very short periods of time. I visited Jason in his laboratory at the newly constructed Peter Doherty Institute, to learn how he develops these simulations. Then I toured the Peak Computing Facility, which houses the supercomputer that calculates Jason’s simulations.


An unexpected benefit of inactivated poliovirus vaccine

Poliovirus by Jason Roberts

Poliovirus by Jason Roberts

The polio eradication and endgame strategic plan announced by the World Health Organization in 2014 includes at least one dose of inactivated poliovirus vaccine (IPV). Since 1988, when WHO announced the polio eradication plan, it had relied exclusively on the use of oral poliovirus vaccine (OPV). The rationale for including a dose of IPV was to avoid outbreaks of vaccine-derived type 2 poliovirus. This serotype had been eradicated in 1999 and had consequently been removed from OPV. However IPV, which is injected intramuscularly and induces highly protective humoral immunity, is less effective in producing intestinal immunity than OPV. This property was underscored by the finding that wild poliovirus circulated in Israel during 2013, a country which had high coverage with IPV. Furthermore, in countries that use only IPV, over 90% of immunized children shed poliovirus after oral challenge. I have always viewed this shortcoming of IPV as problematic, in view of the recommendation of the World Health Organization to gradually shift from OPV to IPV. Even if the shift to IPV occurs after eradication of wild type polioviruses, vaccine-derived polioviruses will continue to circulate because they cannot be eradicated by IPV. My concerns are now mitigated by new results from a study in India which indicate that IPV can boost intestinal immunity in individuals who have already received OPV.

To assess the ability of IPV to boost mucosal immunity, 954 children in three age groups (6-11 months, 5 and 10 years) were immunized with IPV, bivalent OPV (bOPV, containing types 1 and 3 only), or no vaccine. Four weeks later all children were challenged with bOPV, and virus shedding in the feces was determined 0, 3, 7, and 14 days later. The results show that 8.8, 9.1, and 13.5% of children in the 6-11 month, 5-year and 10-year old groups shed type 1 poliovirus in feces, compared with 14.4, 24.1, and 52.4% in the control group. Immunization with IPV reduced fecal shedding of poliovirus types 1 (39-74%) and 3 (53-76%). The reduction of shedding was greater after immunization with IPV compared with bOPV.

This study shows that a dose of IPV is more effective than OPV at boosting intestinal immunity in children who have previously been immunized with OPV. Both IPV and OPV should be used together in the polio eradication program. WHO therefore recommends the following vaccine regimens:

  • In all countries using OPV only, at least 1 dose of type 2 IPV should be added to the schedule.
  • In polio-endemic countries and in countries with a high risk for wild poliovirus importation and spread: one OPV birth dose, followed by 3 OPV and at least 1 IPV doses.
  • In countries with high immunization coverage (90-95%) and low wild poliovirus importation risk: an IPV-OPV sequential schedule when VAPP is a concern, comprising 1-2 doses of IPV followed by 2 or mores doses of OPV.
  • In countries with both sustained high immunization coverage and low risk of wild poliovirus importation and transmission: an IPV only schedule.

Type 2 OPV will be gradually removed from the global immunization schedules. There have been no reported cases of type 3 poliovirus since November 2012. If this wild type virus is declared eradicated later this year, presumably WHO will recommend withdrawal of type 3 OPV and replacement with type 3 IPV.

All 342 confirmed cases of poliomyelitis in 2014 were caused by type 1 poliovirus in 9 countries, mainly Pakistan and Afghanistan. Given the social and political barriers to immunization, it will likely take many years to eradicate this serotype.

The Wild Types

The Wild Types is an interview show about scientists hosted by Ushma Neill and Richard White. Ushma interviewed me for episode #2. The show name doesn’t refer to the fact that all scientists are wild (some are; I am not) but the genetic term referring to the strain or organism that is compared with mutants. As in, ‘the wild type virus was compared with the mutant virus that transmits among ferrets by the airborne route’.


The 100th birth anniversary of Jonas Salk

Peter L. SalkJonas Salk, who lead the team that developed the first poliovirus vaccine, was born 100 years ago today, 28 October 1914, in New York City. Numerous sites across the country have convened symposia in his honor. Last week City College of New York, where Salk earned a bachelor’s degree, held a centennial celebration. The photo shows Salk’s son Peter speaking at the celebration. New York University Medical Center, where Salk obtained his MD degree, also had a celebration last week. The Salk Institute, founded by Jonas Salk, will hold a celebration on 13 November. And today’s Google Doodle is in honor of Dr. Salk.

In honor of Salk’s memory, I’ve included below my interview with his son, Peter, and a list of all the articles on poliovirus from virology blog. If you can only read one, make it Dreaming of inactivated poliovirus vaccine. Then realize that WHO has called for a switch to Salk’s IPV.

Oral polio vaccine-associated paralysis in a child despite previous immunization with inactivated virus

Poliovirus escapes antibodies

Implications of finding poliovirus in sewers of Brazil and Israel

Polio-like paralysis in California

India has been free of polio for three years

World Polio Day

Poliovirus silently (and not so silently) spreads

The wall of polio

Poliovirus on Time

WHO will switch to type 2 inactivated poliovirus vaccine

Virology lecture: Picornaviruses

World Polio Day

Can India remain polio-free?

India polio-free for one year

Wild poliovirus in China

Transgenic mice susceptible to poliovirus

Poliomyelitis after a twelve year incubation period

Poliovirus vaccine safety

Is bivalent poliovirus vaccine a good idea?

Viruses and journalism: Poliovirus, HIV, and sperm

Poliovirus on BBC radio

Poliovirus type 2 returns

Polio returns to Minnesota

Poliovirus vaccine litigation

Polio among the Amish

Dreaming of inactivated poliovirus vaccine

Polio in Nigeria

Polio and Nobel Prizes

Polio in Pakistan and Afghanistan

Jonas Salk’s Poliovaccine


Poliovirus is IRESistable

Vaccines lecture, 2014 (YouTube)

TWiV 308: The Running Mad Professor

On episode #308 of the science show This Week in Virology, Tom Solomon, an infectious disease doctor from Liverpool, talks with Vincent about viral central nervous system infections of global importance, Ebola virus, and running the fastest marathon dressed as a doctor.

You can find TWiV #308 at

Oral polio vaccine-associated paralysis in a child despite previous immunization with inactivated virus

Poliovirus by Jason Roberts

Poliovirus by Jason Roberts

Vaccine-associated poliomyelitis caused by the oral poliovirus vaccine is rare, but its occurrence in a healthy, immunocompetent 6-month old child was highly unusual because the child had been previously immunized with two doses of the injected, inactivated poliovirus vaccine (IPV).

The three poliovirus vaccine strains developed by Albert Sabin (OPV, oral poliovirus vaccine) contain mutations which prevent them from causing paralytic disease. When the vaccine is ingested, the viruses replicate in the intestine, and immunity to infection develops. While replicating in the intestinal tract, the vaccine viruses undergo mutation, and 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 the Sabin vaccine.

To prevent vaccine-associated poliomyelitis, in 1997 the US switched to an immunization schedule consisting of two doses of IPV followed by one dose of OPV. The US then switched to using IPV exclusively in 2000. The child in this case essentially had a polio immunization course similar to that utilized in the US from 1997-2000: two doses of IPV, one dose of OPV. Why did the child develop poliomyelitis?

One clue comes from the fact that after the switch to an IPV-OPV schedule in 1997, there were still three cases of VAPP in 1998 and three in 1999. Another hint comes from a study of immune responses in children given multiple doses of IPV. Most of the children receiving two doses of IPV produced antibodies against types 1 and 2 poliovirus (92 and 94%), but only 74% of children produced antibodies against type 3 poliovirus.

The final piece of information needed to solve this puzzle is that the child in this case had vaccine-associated poliovirus caused by the type 3 strain, which was isolated from his feces.

Therefore, the child in this case most likely did not produce sufficient antibodies to type 3 poliovirus after receiving the two doses of IPV. As a consequence, when he was given OPV, he developed type 3 vaccine-associated poliomyelitis.

This case of VAPP could have been prevented: the child was born in Canada, and as customary in that country since 1995, he received two doses of IPV. At 5 months of age the child and his family visited China, where his parents decided to continue his immunizations according to the local schedule. China still uses OPV, so that is what the child received.