Polio in the water, COVID in the air
And a new henipavirus in China
Greetings from an undisclosed location in my apartment. Welcome to Viral Transmissions.
On August 12th (today) in 1990, Susan Hendrickson discovered the largest complete Tyrannosaurus rex fossil skeleton ever found. This skeleton was nicknamed “Sue,” after its discoverer.
Today we’ll discuss recent findings of polio in New York State and the UK, changes to CDC recommendations regarding COVID-19, and a story about a new virus that has appeared in people in China.
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As a reminder, links that look like this go to the glossary I maintain for this newsletter.
Now, let’s talk viruses.
Langya virus, a new henipavirus
I keep my eyes open for new henipaviruses, because my PhD began with an interest in Nipah virus, the deadliest species in that genus.
Recently, a report came through PROMED-mail (a global disease surveillance system) that indicated a new henipavirus, named Langya virus, had been detected in humans in China, with suspected spillover from wild shrews. I tweeted about it when I saw it:
The outbreak here was characterized in a New England Journal of Medicine letter, describing symptoms found in conjunction with the virus, all mild, but noting that this work itself does not establish that Langya virus caused the disease in question. That will take further work. I’m encouraged, so far, that it doesn’t seem to cause serious disease—if it causes any disease at all.
It’s interesting to me to see this because with very mild illness I would not have expected, say, 10 years ago, for something like this to be detected. If nothing else, the detection of this novel virus says to me that virus surveillance in the post-COVID world has improved. We haven’t learned a lot of lessons from the pandemic, in my opinion, but if we’ve improved our overall disease intelligence infrastructure, that’s probably a good thing. I just wish it hadn’t come at such a high price.
Polio
Some weeks back, there was a news story about detection of poliovirus in London wastewater. This started a conversation in various quarters about polio and polio vaccination that was very timely, considering that not long afterwards a paralytic case of polio was discovered in an unvaccinated person living in Rockland County, New York.
In light of these developments I wanted to take a moment to discuss polio vaccines and vaccination, which have some features that we are already familiar with from the COVID-19 experience.
In COVID-19, a lot of words have been written and said about the differences between sterilizing immunity vs protective immunity. Sterilizing immunity prevents infection altogether. Protective immunity prevents disease. If someone has protective immunity, this does not necessarily mean they are unable to spread a disease to others. With sterilizing immunity, however, since there is no infection there is no chance for subsequent spread. On the other hand, there are vaccines that limit contagion without necessarily providing sterilizing immunity.
For viruses that infect non-skin interfaces between the body and the outside environment (aka “mucosa”), a separate domain of immunity called mucosal immunity is important for achieving a sterilizing response. I’ve discussed this in past issues when talking about the ability of COVID-19 vaccines to prevent infection with SARS-CoV-2. Without mucosal antibodies and mucosal immunity, it appears to be hard to achieve sterilizing immunity against SARS-CoV-2 and the disease it causes. Protective immunity, however, can be achieved.
A similar problem occurs in polio vaccination. Most people think of polio as a disease characterized by severe paralysis that can become permanent. In fact, paralytic polio occurs in just 1% of people who become infected with poliovirus, the agent which causes the disease. As many as 70% of infectees are asymptomatic, and the remainder generally experience mild symptoms such as fever. However for that 1% who experience paralytic polio, the effects of the disease can be devastating, if not deadly.1
Why is there such a huge difference in the types of poliovirus-mediated disease that people get? Well, it may surprise you to learn that poliovirus does not primarily infect the nervous system. In fact, poliovirus is a subtype of enterovirus C, which is named an “enterovirus” because of its propensity to infect enteric—intestinal—tissue. In other words, poliovirus infects our guts, at least most of the time.
In some polio infections, the virus becomes able to infect cells of the central nervous system, though it is not totally understood exactly how this happens. Once it does happen, however, it becomes possible to get paralytic polio.
This narrative of how poliovirus causes severe paralytic illness is important also to our vaccination strategies against this virus. There are two polio vaccine types that are in use around the world, both named for their original inventors. The first, inactivated polio vaccine (IPV), is also known as the “Salk vaccine” for its inventor, Jonas Salk. IPV is an injected vaccine that uses inactivated poliovirus, so it is incompetent to cause any infection.2
The other vaccine option is the oral polio vaccine (OPV), which is also known as the Sabin vaccine, for its inventor, Albert Sabin. This vaccine is a “live attenuated” design, wherein the virus has been weakened by mutation in nonhuman tissue culture to the point where it cannot cause human disease. If you live in a country that uses OPV, or you were born in the US before a certain year, you may remember being given a vaccine that was dropped onto a sugar cube and then ingested—that’s OPV.3 It can also be administered orally by dropper into the mouth, as seen here:
Each vaccine has advantages and disadvantages. IPV, being injected, generates immunity in the bloodstream and thus is protective against paralytic polio but does not produce sterilizing immunity because it does not yield mucosal immunity. When poliovirus is encountered, it can still infect the gut of a person who has received IPV, be shed by that person, and find its way into wastewater.
OPV, meanwhile, can generate mucosal immunity. However, it has a couple of other problems. The attenuation that is generated by passage in nonhuman cells can revert, and a functional, vaccine-derived poliovirus can result. This vaccine-derived poliovirus is usually harmless to the vaccinee, but can still be shed into the environment. If it then encounters a person who is not immune to polioviruses, it can replicate in that person and even cause disease. This happens very rarely and generally requires poor sanitation and low overall vaccination rates in the community.
This also happens to be the source of the wastewater detection in London, and the case that was seen in New York.
What’s interesting about the New York case, however, is that OPV is not given in the US and the individual with paralytic polio did not have recent travel. So how did they get vaccine-derived polio? The CDC is investigating, but this is the most plausible narrative:
Since 2000, only IPV is given in the US. People who received IPV are protected from paralysis, but not from infection, and can acquire vaccine-derived or any other form of poliovirus.
OPV is given in many other countries, and so vaccine-derived poliovirus can be found in wastewater in these countries and can infect people via the usual ways that polioviruses can spread
A person from the US might have acquired vaccine-derived poliovirus while traveling abroad, and brought it back here, where it could readily spread in other IPV-vaccinated individuals (which includes just about every US-born person who is 22 years old or younger, as well as some who are older than that)
Eventually, this vaccine-derived circulating poliovirus strain encountered the Rockland County patient who was unvaccinated, and cause paralytic polio in this person
The acquisition of this one paralytic case suggests that there are at least a hundred, if not many more, other cases that aren’t paralytic—but these could be in people who are vaccinated
This situation where an IPV-OPV interaction creates an issue for efforts to eradicate polio. It is not clear how long OPV-derived poliovirus can persist in water, and since we continue to use this vaccine globally, there are now more incidents of transmission of vaccine-derived polioviruses than there are of wild polioviruses. However, if we keep using OPV, we will keep generating more poliovirus in wastewater. Meanwhile, if we switch to IPV entirely, we create a population that is permissive to infection with vaccine-derived polio.
But what if, like me, you were vaccinated against polio as a child and now you live in a place where polio cases have been identified? Well, you are most likely protected against paralytic polio. However, it has historically been recommended—and that recommendation has recently been reiterated by New York State health authorities—that adults who are traveling to places that have cases of polio get a booster dose of vaccine. See, for example, this very recent statement that includes this advice: https://www.health.ny.gov/press/releases/2022/2022-08-12_nys_nyc_wastewater_polio.htm#:~:text=Children%20and%20adults%20should%20be,there%20is%20a%20poliovirus%20transmission.
This is not a bad idea. While cases of paralytic vaccine-derived polio in vaccinated people are exceptionally rare, it might be worth a conversation with your healthcare provider if you live in areas near Rockland County in New York. However do keep in mind that this virus was clearly already circulating in that area and so far only caused any disease in an unvaccinated person, despite presumed access to a large number of vaccinated hosts in the same region.
CDC gets relaxed about COVID-19
This is very new information, but in the last 24 hours the US CDC has relaxed a lot of its COVID-19 recommendations. I am still digesting the new guidance myself, but the bottom line is that the CDC has considered three facts about COVID-19 that I do agree with, and come to conclusions based on those facts that I am not at this time sure that I agree with. These are the facts:
Population immunity to COVID-19 has led to substantial reductions in hospitalizations and deaths as a percentage of total infections, and the rate of hospitalizations and deaths does not appear to be substantially changing despite the ebbs and flows of case numbers (this is being called “decoupling”)
COVID-19 is not going to be eradicated anywhere
Vaccination has apparently lowered rates of both acute symptoms and longer-term, post-acute symptoms in those who have gotten vaccinated
In light of that, the CDC has decided that we need to set a new goal for the US approach to the COVID-19 pandemic. Instead of trying to contain all spread of COVID-19, they are focusing on reducing the incidence and prevalence of severe disease. In light of this focus, CDC guidance has been modified to do the following (all points taken verbatim from CDC release):
Continuing to promote the importance of being up to date with vaccination to protect people against serious illness, hospitalization, and death. Protection provided by the current vaccine against symptomatic infection and transmission is less than that against severe disease and diminishes over time, especially against the currently circulating variants. For this reason, it is important to stay up to date, especially as new vaccines become available.
Updating its guidance for people who are not up to date on COVID-19 vaccines on what to do if exposed to someone with COVID-19. This is consistent with the existing guidance for people who are up to date on COVID-19 vaccines.
Recommending that instead of quarantining if you were exposed to COVID-19, you wear a high-quality mask for 10 days and get tested on day 5.
Reiterating that regardless of vaccination status, you should isolate from others when you have COVID-19.
You should also isolate if you are sick and suspect that you have COVID-19 but do not yet have test results.
If your results are positive, follow CDC’s full isolation recommendations.
If your results are negative, you can end your isolation.
Recommending that if you test positive for COVID-19, you stay home for at least 5 days and isolate from others in your home. You are likely most infectious during these first 5 days. Wear a high-quality mask when you must be around others at home and in public.
If after 5 days you are fever-free for 24 hours without the use of medication, and your symptoms are improving, or you never had symptoms, you may end isolation after day 5.
Regardless of when you end isolation, avoid being around people who are more likely to get very sick from COVID-19 until at least day 11.
You should wear a high-quality mask through day 10.
Recommending that if you had moderate illness (if you experienced shortness of breath or had difficulty breathing) or severe illness (you were hospitalized) due to COVID-19 or you have a weakened immune system, you need to isolate through day 10.
Recommending that if you had severe illness or have a weakened immune system, consult your doctor before ending isolation. Ending isolation without a viral test may not be an option for you. If you are unsure if your symptoms are moderate or severe or if you have a weakened immune system, talk to a healthcare provider for further guidance.
Clarifying that after you have ended isolation, if your COVID-19 symptoms worsen, restart your isolation at day 0. Talk to a healthcare provider if you have questions about your symptoms or when to end isolation.
Recommending screening testing of asymptomatic people without known exposures will no longer be recommended in most community settings.
Emphasizing that physical distance is just one component of how to protect yourself and others. It is important to consider the risk in a particular setting, including local COVID-19 Community Levels and the important role of ventilation, when assessing the need to maintain physical distance.
The biggest changes here are that distinctions between vaccinated and unvaccinated people are now, essentially, gone. Sick people should isolate, and very sick people should isolate for longer. If symptoms return (aka “rebound”), isolation should be resumed.
Healthy people should no longer be tested routinely for asymptomatic infection, but masks are recommended for use for a period of days after potential exposure—instead of quarantining.
On the whole, these changes substantially improve conveniences for people who have good immunity against COVID-19 and are not likely to experience severe disease. On the other hand, they require that anyone at substantial risk rely on vaccination and one-way masking for protection from COVID-19 going forward. Yes, there are some circumstances where the new CDC guidance seems to expect two-way masking, but I do not expect compliance with that to be universal, or even common. Still, if you’re reading this, then I can implore you: if you’ve been around someone who has COVID-19, wear a mask for 5-10 days. Make that mask an N95 or equivalent. If you’ve had COVID-19 but are getting better, limit how often you go out and wear an N95 or equivalent mask until at least 10 days have passed. If you’ve had severe COVID-19 or have been hospitalized, don’t go out until your doctor(s) agree you can.
It’s possible to react to these changes and say that the CDC is effectively admitting defeat against COVID-19, but I think that’s as unfair to say as the opposite statement that the CDC is finally admitting that COVID-19 is over. Neither of these things is true. The US and world population is now more immune to COVID-19 than it has ever been, but that immunity is not perfect. It’s still important to protect oneself and others, and vaccination and masking are still a part of that strategy. But, in the view of the US CDC at least, masking, testing, and isolation for certain types of healthy people are now measures that are too extreme to justify the benefits.
Again, I still don’t know the extent to which I agree with this. But I’m possibly not as far off this position as some might think. There are settings where I think it’s still important to mask—large indoor crowds, travel settings, or if you are around or are personally someone with high COVID-19 risk—but there are also settings where I don’t think it is accomplishing much. I wear my mask at the grocery store, because it affects me negatively in zero ways while potentially helping others. But in the meantime, I’d be OK eating in a smallish restaurant4 given my vaccinated, boosted, and recovered status. But that’s based on my unique situation, the geography where I live, and the vaccination demographics of my home.
I do want to call attention to one point of the CDC’s guidance that I found interesting—the last one. Where they mention that community levels and also local ventilation should be considerations when evaluating risk. They also distance themselves from physical distancing. This is a statement that the CDC has not made before, and I think acknowledges the reality that COVID-19 spreads through the air, something that the CDC has been unclear about before. I’ve long counseled people to think about airflow, masking, and community prevalence rather than worrying about 6 feet of distance, and even if I don’t agree with the rest of this, I am glad to see the CDC coming around on this point in particular.
It’s been a quiet week for me. I recently picked up some “Cuban-style Citrusy Garlic” seasoning from Trader Joe’s, and I can report that it’s really great on fish. Helped me get a nice, flavorful crust on some Chilean sea bass that I found on sale and seared for dinner last night.
I hope you’re all doing well. Today’s polio discussion was based on reader interest, so please keep your comments coming.
As I’ve said throughout, I want to hear from you, too, with your questions about monkeypox, or COVID-19, or just updates about your lives. This newsletter is a community. Reach out!
I have a commitment to accuracy, but I’m still human and I get things wrong. Sometimes, very wrong. If you catch an error, let me know—you can email me directly or leave a comment.
Thanks for reading today. It’s great to be writing to you again. Have a wonderful weekend!
Always,
JS
Without medical attention, around 5 to 10% of people with paralytic polio will suffocate due to paralysis of muscles needed to breathe.
The inactivation process is very important. Early in the history of the Salk vaccine, a manufacturing error led to improper inactivation of the virus, and so thousands of children were injected with poliovirus instead of a vaccine against poliovirus. 56 cases of polio resulted, with 5 deaths. This is known as The Cutter Incident, and was discussed at length in a book by famed vaccinologist Dr. Paul Offit.
The use of sugar cubes to administer OPV was the inspiration for the famous song “A Spoonful of Sugar” in the Mary Poppins film: https://insidethemagic.net/2020/12/spoonful-of-sugar-sherman-lp1/
I live in New York City, so this is effectively every restaurant.
I'd like to hear (read) your thoughts on the FDA's decision to stretch the MPV vaccines by giving them intradermally.
On the topic of sterilizing immunity and COVID, what do you think of the Mambisa vaccine? It's a Cuban intranasal vaccine that seems to work pretty well, but I can't find anything on it's potential to stop transmission and provide sterilizing immunity. Are there any IN vaccines that have shown promise? I am holding out for such a vaccine! I want it!