Volker writes:
Dear TWiV Team,
I just listened to episode 1235 and was surprised that sanitation did not feature in the discussion about polio eradication. As I understand it, countries using only IPV (which does not induce mucosal immunity) still report almost no poliovirus in wastewater (whenever they do analyse it), despite recurring importations from regions where polio is circulating.
To me, this suggests that the effective reproduction number (R) remains below 1 in these settings—likely due to sanitation and hygiene standards interrupting fecal–oral transmission. Otherwise, we should expect ongoing silent transmission and detectable poliovirus in wastewater, given the absence of mucosal immunity.
From this perspective, it seems that eradication in low-income countries cannot rely on vaccination alone but also requires improvements in sanitation to drive R below 1—whether in combination with IPV, OPV, or transition strategies.
If you see an alternative explanation for the scarcity of poliovirus in wastewater in IPV-only countries that does not rely on sanitation, I would be very interested to hear it.
Thank you for your work and for consistently grounding the discussion in science.
Best regards and greetings from Bavaria,
Volker
Response:
It would be greatly appreciated if one does not refer to virus reproductive numbers as they are not an intrinsic property of any virus and its meaning is dubious at best.
The continued transmission of poliovirus in low-income countries is due to poor vaccination coverage and some misunderstandings about poliovirus transmission and immunity. Sanitation conditions in these countries have significantly improved and poliovirus continues to circulate. Outbreaks of paralytic poliomyelitis in the US during the 1900s were not due to poor sanitation conditions but a consequence of poor population immunity and the fact that you can productively get re-infected by the same serotype – ie. the virus reproduces and is shed by those individuals. This fact remains true for all vaccinated individuals. The reason for the outbreaks of the 1900s was that improved sanitation conditions delay when children are initially infected by the virus. In fact where sanitation conditions remained poor, there were fewer cases of paralytic poliomeylitis. Children living with improved sanitation conditions were generally infected when they are no longer protected by the presence of maternal antibodies. As one ages, the probability of developing paralytic poliomyelitis increases. In many of these low income areas where poliovirus continues to circulate it is likely to be found circulating within vaccinated populations.
The role of mucosal immunity for reducing virus shedding is unclear. Early work examining virus shedding in infants following OPV administration suggested that gut immunity reduced the duration of virus shedding. The studies done in older populations suggest that mucosal immunity does not affect virus shedding. IPV or OPV vaccinated adults shed virus with the same kinetics. Furthermore there are data that suggest IPV can induce mucosal immunity or that IPV stimulates anti-poliovirus immune cell migration into the nasopharynx. The detectable level of mucosal immunity in these cases is thought to depend upon the number of doses of IPV one receives. However, because mucosal immunity is underneath the level of detection by our laboratory assays does not mean it is not present and functional. Nevertheless, in their recent CID editorial, Plotkin and Chumakov correctly state that mucosal immunity fades. Studies in the 1960s when virus circulated revealed that IPV reduces the duration and magnitude of virus shedding; however, now that virus circulates in only a few places, the probability of someone shedding following IPV is similar to that of unvaccinated. If you do shed, the kinetics are similar to that of OPV.
The scarcity of poliovirus detection in the wastewater in IPV-only countries does not rely on sanitation, ie sewer systems but high vaccination coverage and high population immunity. If you were to stop vaccinating in IPV countries you would see outbreaks of paralytic disease and extended virus transmission and circulation. Sanitation in these countries would not have changed. This week alone 8 environmental samples in Germany were positive for cVDPV2 and 6 sites in Israel were positive for cVDPV1. The last positive tests reported were in early 2025 for Germany and Dec. 25 2024 when a patient in Israel was diagnosed with paralytic poliomyelitis due to cVDPV2 infection…….did all the toilets and closed sewer systems just overflow this week?
IPV only countries infrequently survey for poliovirus as well as on a country level have high vaccine coverage and population immunity. Poliovirus is imported and more often than not, the virus burns itself out by acting as a booster by infecting vaccinated individuals; consequently it circulates for a very short period of time. Only when the virus circulates in an under immunized population and a case of paralytic disease is detected do we know of its circulation.
David writes:
Were Zappa still with us he would be posting this on line:
Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe.
There is more stupidity than hydrogen in the universe, and it has a longer shelf life.
ME: It’s like the law of partial pressures for gas: get rid of science to make more room for stupidity.
David J. Davin MD
James writes:
Hello Vincent, et al
Shortly after posting this, an email from STAT containing, among other articles, one by Branswell. https://www.statnews.com/2025/07/23/h5n1-bird-flu-immunity-boosted-by-previous-influenza-a-infection/
New study advances theory on why most U.S. bird flu cases have so far been mild
Researchers believe immunity to an earlier virus may play a role, but not everyone agrees
Indeed, count me in as one the skeptics.
Yoshihiro Kawaoka, a leading influenza scientist at the University of Wisconsin-Madison, is among those who are skeptical, pointing to H5N1 infections in Cambodia, which has reported
who.int/emergencies/dis…who.int/emergencies/dis…, 12 of which have been fatal. The version of the virus circulating in that country is different from the one that has been infecting cows and poultry in the United States.
Kawaoka believes a number of other factors may explain differences in the severity of cases, including differences in the viruses, the way dairy workers and poultry cullers are being infected — often, it seems, with virus entering their eyes — or the ages and underlying health of the people who are being infected.
I have been making notes in my posts that the eyes have the Avian α-2,3-linked SA receptors (as you have pointed out), the upper respiratory system is almost all the human α-2,6-linked SA receptors.
Sort of self limiting infection. Further, confirmed cases were treated with antiviral oseltamivir. I believe this was spread by contact, ‘Milk snatching’ flies being one culprit.
Richard Webby, another one I respect, had this to say, “I don’t want to downplay the study because it’s an important study. But it’s just explaining a part of the puzzle. It’s absolutely not explaining everything we’re seeing,” he said.
“We know that seasonal influenza viruses transmit just fine in the human population where there is a lot of preexisting immunity. So preexisting immunity in its own right is not enough to prevent an influenza virus from transmitting through the population.”
Still, if it makes the transition to human RBD, hope for the best?
Would like to hear from TWIV or Immune on this.
James
Ted writes:
Hi TWIV,
Many thanks for keeping us all informed! I’m a regular listener to the Sat. show and, occasionally, others.
Recently contracted COVID as I began a stay at our cabin with an outhouse. Any concerns about the virus survival in contained outhouse waste. The outhouse was recently serviced. I also started Paxlovid on day 3. Will Paxlovid antiviral negate any waste issue? Best to add anything?
Also, while I fortunately had an unexpired series of Paxlovid, I was shocked at the price increase to 1k to 1.5. This will make the best antiviral inaccessible to most. Sad.
Best, Ted
Ardmore, PA
Linda writes:
Vincent
For those who were Star Trek fans, the recent news article in Science (June 12 2025) will be of interest. Attached is a PDF of the article.
It describes a device that samples the air, collects the eDNA, sequences it and used this info the identify what life forms were in this environment.
Star Trek fans will remember this is what the Tricorder could do. It would sample the air and tell you what lifeforms existed on that planet
An avid listener
Linda
