Johan writes:


Just wanted to say that I appreciate the last two episodes from KI (What we always call the Karoliska Institute). As a Swede I often think the show is a bit too US centric, so I really enjoyed these episodes.


Skickat från min iPhone

Mike writes:

Dear TWIV,

I love the show—especially how you emphasize breadth and connections—but there is something slightly wrong on the internet I’m compelled to fix. Politely, Vincent and Alan drive me a little nuts whenever they talk about the differences between IPV and OPV for polio eradication. 

Both are of course correct that OPV (oral polio vaccine, Sabin vaccine) has been used by the eradication program because it’s cheaper and easier to deliver than IPV (inactivated polio vaccine, Salk vaccine)—drops in the mouth vs a needle in the arm makes a big difference on logistics and per dose cost. And yes, there is an acute IPV supply shortage that makes replacing OPV with IPV even more difficult right now.

However, these are not the only reasons the polio eradication program still uses OPV. There is a deep epidemiological reason as well—OPV is more effective than IPV against transmission in much of the world.

The very short version of it is that OPV is good at preventing infection and paralysis, while IPV alone is only good at preventing paralysis but not infection. People who’ve only had IPV are as susceptible as unvaccinated people to infection when exposed. Thus, in places where exposure to poliovirus is common, a population only vaccinated with IPV will be easily infected, and people who remain unvaccinated—most often due to systemic failures and not their own willful refusal—will be unprotected. Thus, if you want to protect everyone even when immunization programs are not reliable, you need OPV and herd immunity to achieve that.

If you want the short-but-not-very-short version, notice there’s a nuance hidden in the previous paragraph: “when exposed.”  The tricky thing is while IPV alone doesn’t block infections, and so people with only IPV will shed lots of poliovirus in their stool, IPV does block shedding in saliva. This means that the impact of IPV on transmission depends on sanitation. If sanitation is good enough, you can have a country full of people who’ve only had IPV who would get easily infected if they are exposed, but they never get exposed. Someone who got infected while traveling can pump poliovirus into the sewers as much as they want, but no gets exposed to that material, and so there is no transmission. This is why IPV can produce herd immunity in places with adequate sanitation—it blocks exposure where saliva is the primary medium of exchange. 

This quirk of sanitation interacting with transmission routes and immunity explains why the only places on earth that eliminated poliovirus with IPV alone were in Scandinavia (this probably plus winters especially inhospitable to poliovirus). And trends in sanitation explain why countries like the US couldn’t eliminate with IPV alone in the 1950s but can keep polio out today. Israel, which used only IPV since 2006, has populations on the cusp. They had an outbreak in 2013-2014 where no one got paralyzed—sewers in multiple cities showed circulating poliovirus for about a year—and temporarily restarting OPV swiftly ended the outbreak.

In places where sanitation is especially poor, switching to IPV alone will leave populations with no herd immunity whatsoever. That’s the most important reason why the eradication program needs to rely on OPV. OPV is still necessary, until poliovirus is either eradicated or global sanitation standards reach developed-world levels.

But great podcast!


Mike Famulare, PhD

Principal Research Scientist, Co-chair Epidemiology

Institute for Disease Modeling

PS. Believe it or not, this is the short version of the email. I tried to write slightly longer version but it was turning into the discussion of a paper my colleagues and I published last year, so I encourage those interested to just read that ( Forgive the shameless self-promotion). 

What’s the typo-equivalent of l’esprit de l’escalier?



Theodore writes:

Dear TWIV,

My name is Theodore, and I am a graduate student at Drexel University. I had a question about the current HIV-1 cure strategy used to cure the Berlin and London patients. Currently, it is possible to delete the CCR5 co-receptor in stem cells to prevent CCR5-tropic HIV-1 from infecting CD4+ cells. However, to my knowledge, it is not possible to delete the CXCR4 co-receptor without severely harming or killing the patient, thus it is not practical to delete the CXCR4. Does TWIV think the cure strategy of hematopoietic stem cell transplant used for the Berlin and London patients is capable of being used to cure patients infected with CXCR4-tropic HIV-1, if so how?

Thank you,


John writes:


I first learned of your podcast(s) thru the now defunct Science360 Radio. S3R introduced me to all your podcasts and so many others. 

I’m a mechanical engineer/frustrated scientist and so enjoy the scientific & technical banter.

Didn’t know if you heard that S3R was going silent. 

I’ll surely continue listening though 



Anthony writes:

2019 Education Award

“Expanded the universe I lived in beyond home, school and the mall”

Leigh Bardugo On ‘Ninth House’

# # #

The author here is talking about Fantasy and Science Fiction.  While in high school, I read a lot of Edgar Rice Burroughs, Robert Heinlein and similar time wasters — like eating chocolate in the hope of acquiring trace minerals.  

I’m glad that everyone — particularly students — has access to your work as wings to escape like Daedalus from the prison of a narrow world.

Thank you.

Ryan writes:

This is as SB 276 is underway here in California and debates are underway in other states to see if they should do the same in 2020.

SACRAMENTO —  Californians strongly support a state law creating new oversight of vaccine medical exemptions for schoolchildren in a statewide poll released Monday, with backing across a spectrum of political affiliations, income and education levels, and geography.

The UC Berkeley Institute of Governmental Studies poll, conducted for the Los Angeles Times, found that 90% of Democrats, 82% of those with no party preference and 73% of Republicans supported the effort to increase immunization rates at schools and day-care facilities by allowing the California Department of Public Health to review and possibly reject a doctor’s determination that a child should skip all or some of their shots.

Overall, 8 out of 10 voters surveyed said they supported the new law, with 61% saying they favored it strongly. Just 16% said they opposed it. The strongest dissent came from participants in the poll who described themselves as very politically conservative — 1 out of 3 of those voters said they opposed it.

Still, 67% of conservative voters who participated overwhelmingly supported the vaccination law, said Mark DiCamillo, director of the Berkeley IGS poll.

Justin writes:

not related to this project at all but I absolutely love mass spec and this blows my mind

Mark writes:

Hello TWiV-pro-vaxxers,

The weather here in California has cloudy mornings, sunny and warm afternoons, aka fall season boring. Just another shitty day in paradise.

First: tonight I received my vaccination for 2019 flu. Have any of you?

Second, Vincent, I need to correct a grievous error you made in TWiV 566. You said the Ford Mustang came out in 1962. no, No, NO! It was launched in 1964. Lee Iacocca, Ford’s marketing manager for the launch, coined the famous “$64 in ‘64” slogan to entice buyers to finance the car at then affordable monthly payments. It’s success launched his career, and burned the Mustang into our culture.
Third, a follow up question. You all were discussing mutation in DNA viruses. What is their error rate? In many prior shows its been mentioned that RNA viruses have an error rate of 10^-4. What is it for DNA viruses?

Fourth, my listener pick of the week is this story from the New York Times. It’s really first rate investigative journalism digging into the many issues — pilot training, Boeing’s development culture, government inspection, unexpected consequences, and more — surrounding the Boeing 737 Max plane crashes:

Fifth, my listener anti-pick of the week. In some banter you all talked and joked about boring people. Self-defenestrated James Watson wrote a book titled “Avoid Boring People” which shows him at his supercilious best.


YouTube interview about it:

All the best.