COVID Transmissions for 2-18-2021
Real-world data from Israel begins to show effects of vaccines on viral load
Good morning and welcome to COVID Transmissions.
It has been 458 days since the first documented human case of COVID-19. The planet Mercury has orbited the Sun 5.2 times since COVID-19 first emerged in humans.
As usual, bolded terms are linked to the running newsletter glossary.
Keep COVID Transmissions growing by sharing it! Share the newsletter, not the virus. I love talking about science and explaining important concepts in human health, but I rely on all of you to grow the audience for this, which you can do by using this button here:
Now, let’s talk COVID.
The Israeli experience suggests a drop in viral load with Pfizer vaccination
I’m happy to be able to share with you some results from a preprint (not peer reviewed) on real-world data from Israel. I’d like to thank the reader who sent this paper to me, who I’m keeping anonymous because the communication was not public.
I recognize that you may have a political opinion about Israel, one way or another. Please put it aside, because this is not about Israel as a political entity. This is about Israel as a virus-control experiment, and the country itself is not the important part here. The Israeli experience is one to watch, because Israel has deployed vaccines effectively to a very large percentage of its population. By the time of the study, 75% of people in the over-65 age group in Israel had been vaccinated, while 25% of people outside of this group had been vaccinated.
These are pretty substantial percentages compared to a lot of countries. At this level we can start to get some understanding of how the vaccines might affect transmission dynamics.
There are a few things we need to talk about first, though.
One, the Israeli vaccination program is focusing on use of the Pfizer-BioNTech vaccine. The results I am describing are about that vaccine and should not be extended to any other vaccine; there is reason to believe they would be similar to the Moderna mRNA-1273 vaccine, but I would not cross-compare with any other vaccines based on different technologies.
Two, we need to be sure we are not confusing “viral load” with “transmission of virus.” This is a mistake I have seen a lot lately. Right now we do not have a very clear sense of how viral load—as measured by counting genomes via RT-PCR—translates to transmissibility of virus from an infected person. It is clear that there are some genome copy numbers, which I am calling “viral load” for convenience, at which transmission is very unlikely. I don’t believe that it is definitively confirmed what the level of this is, though I’ve heard some ideas of where it might be from various sources. This study looked at the viral load by RT-PCR in vaccinated patients who became infected. By necessity, this means they were looking at patients who tested positive by PCR. Since we have seen (limited) evidence that these vaccines can reduce infection altogether, we are already biasing our sample by only looking at positive patients. If the vaccines are working very well, there will be fewer PCR-positive patients among vaccinated people. We’ll come to that, but I needed to make sure we all understand that we are looking at the number of virus genomes found in people who tested positive.
Specifically, the study looked at people 65 and older who tested positive in a period spanning December and January, as well as people younger than 65 who tested positive in that same span. They did not have information on the vaccination status of anyone in either group. To determine vaccine effects, instead they relied on the timing of vaccine rollout. Since they knew that by late January, there began to be substantial numbers of over-65 patients vaccinated in Israel, their hypothesis was that by late January, the average RT-PCR viral load in the older age group would start to go down relative to the younger age group.
As it turned out, their hypothesis was correct. By late January, the average RT-PCR viral load in the two groups started to go down for the older patients but did not go down for the younger patients:
This an interesting finding, but I think it’s not really enough to be definitive. We are only looking at PCR-positive patients here, we are relying on estimates because we don’t know who in these groups actually had received the vaccine, and I don’t think viral load is a perfect thing to measure if we want to see effects on transmission.
That said, this points to the idea that vaccination has an effect on the viral load. This means there could be an effect on transmission, and it also helps to potentially explain why vaccination is limiting to disease. Understanding the reason that vaccination can limit disease is very important. Without this information, we could imagine that the vaccine doesn’t necessarily control virus but instead controls the symptoms of virus infection. Instead, we see that it probably does both—we already knew it prevents disease, and here we see indirect evidence that it reduces viral loads.
You can read the full study here, but be aware it is a preprint and has not yet gone through peer review: https://www.medrxiv.org/content/10.1101/2021.02.08.21251329v1
This helps to build the case that this vaccine controls the virus infection happening within a patient, which is a strong argument to suggest it might prevent transmission as well.
I’m going to continue to share information from the Israeli experience throughout this week, so that we can go through it in depth together. There is a lot to learn here about the future for other countries, particularly those relying on mRNA vaccines, from what is happening in Israel.
What am I doing to cope with the pandemic? This:
Watching: The Sinner
The Sinner is a difficult show to watch. It’s a crime thriller series that takes on a different storyline each season—an anthology show in the sense that American Horror Story is an anthology show. But The Sinner has a very different feel. It’s about a detective who uses very unorthodox methods (played by Bill Pullman) and gets too close to the suspects in the crimes he investigates, which gives us a vehicle to explore what makes human beings do violent and unacceptable things. It’s provocative and disturbing, and I think it’s very interesting. It’s not for everyone. If you don’t like heavy things, if you have experiences with trauma that don’t take well to dark content, or if crime dramas aren’t your thing, I wouldn’t recommend it. But if you like deep psychological explorations of people who do wrong, you might enjoy it.
You might have some questions or comments! Send them in. As several folks have figured out, you can also email me if you have a comment that you don’t want to share with the whole group.
Join the conversation, and what you say will impact what I talk about in the next issue.
Also, let me know any other thoughts you might have about the newsletter. I’d like to make sure you’re getting what you want out of this.
Part of science is identifying and correcting errors. If you find a mistake, please tell me about it.
Though I can’t correct the emailed version after it has been sent, I do update the online post of the newsletter every time a mistake is brought to my attention.
No corrections since last issue.
See you all next time.
Always,
JS
Where we able to see an effect on new hospital admits for the 65+ group? For example, did we see a disproportional decline in hospitalizations for 65+ patients relative to the other age groups, and if so, when did that begin, at what vaccination percentage of the 65+ age group? This is a question we are struggling with in NYC.