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Aaron Richterman, MD Profile picture
@AaronRichterman
Jul 31, 2021 • 10 tweets • 5 min read • Read on X
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The question at hand: what is the relative transmission potential of a vaccinated person who becomes infected with delta? This 👇new report from Singapore is much more informative on this question than the CT data released so far from Ptown and Wisconsin.
medrxiv.org/content/10.110…
First, importantly, reducing transmission potential of a person who becomes infected is only one component on the transmission reduction effect of the vaccines. The other: reducing the likelihood of becoming infected in the first place. We discuss here👇
academic.oup.com/ofid/advance-a…
We still await definitive evidence from systematic sampling on the ? of overall infection risk reduction with vaccination, but w strong protection vs symptomatic disease, expect that there will still be substantial protection (50+%) vs overall infection
nejm.org/doi/full/10.10…
Back to the Singapore data - these investigators report features of 218 people hospitalized with delta (all covid is hospitalized in Singapore). 84 had received an mrna vaccine (71 fully vaccinated). Unlike ptown/wisconsin data, can see that vaxed significantly older.
Like ptown/wisconsin data, the CT values at diagnosis are similar (~19). This is 1 piece of data suggesting viral loads *might* be similar at diagnosis. However, there are a number of impt factors that continue to suggest substantially reduced transmission potential among vaxd:
1st, the pattern of CT measurements suggests more rapid viral decay (left). For alpha, increased transmission risk vs ancestral virus was mediated by longer (not higher) peak viral load (right, dash.harvard.edu/handle/1/37366…). We don't know this yet for delta, some think an earlier peak
2nd, the vaccinated ppl infected with delta had greatly reduced symptoms (left=unvax), including a much greater likelihood of being asymptomatic. This will have substantial effect on transmission potential. Some refs: pubmed.ncbi.nlm.nih.gov/33484843/
thelancet.com/journals/lance…
3rd, antibody testing showed high levels of neutralization activity in the vaccinated ppl who were infected. This is the most hypothetical mechanism of reduced transmission potential, but if this neutralization is occurring in the upper airway it is very plausible.
So, transmission reduction is much more complicated than the CT value at diagnosis. That why things like this 👇 are so misleading. If interested, discuss many more details here with @EricMeyerowitz and @mugecevik : academic.oup.com/ofid/advance-a…
Broken link at the top, here is the study
medrxiv.org/content/10.110…

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More from @AaronRichterman

Aaron Richterman, MD Profile picture
May 31, 2023
Over 100 governments in low- and middle-income countries have introduced anti-poverty cash transfer programs over the last 3 decades

In new research, we examined the effects of these initiatives on the ultimate health outcome — mortality

Published today in @Nature /1 Image
We used >80 national surveys in 37 low- and middle-income countries to create longitudinal survival datasets for 4 million adults & 3 million children 2000-2019

About 1/2 the countries started cash transfer programs, & 1/2 the programs were unconditional (no strings attached) /2 Image
We used difference-in-difference models to show these programs led to a 20% reduction in mortality for women, and an 8% reduction in risk of death for children under 5
/3 Image
Read 8 tweets
Aaron Richterman, MD Profile picture
Nov 16, 2021
New pre-print from @EricMeyerowitz and me reviewing loads of new Delta transmission data.

One area we cover — updates on vaccines' effects on transmission in the Delta era 🧵 1/24

papers.ssrn.com/sol3/papers.cf…
First, to review, vaccines can provide:
-direct protection (reduction in infx/disease among vaccinated ppl)
-indirect protection (reduction in infection among all community members through ⬇️ transmission)
/2
nature.com/articles/s4157…
Indirect protection can be generated by
1) ⬇️ risk of infection (if person not infected, cannot transmit)
2) ⬇️ infectiousness of vaccinated person w infection

Prior to delta, 1) + 2) = substantial transmission reduction of 75%+. Our pre-delta review:
/3
academic.oup.com/ofid/advance-a…
Read 24 tweets
Aaron Richterman, MD Profile picture
Aug 24, 2021
As @mugecevik points out, despite the recent proliferation of vaccine studies using routinely collected testing data, the majority of these cannot be reliably be used to estimate VE vs all infections because they do not use systematic testing and/or control for confounding.
Vaccine protection against all infections is one important way (of several) that vaccines reduce transmission (discussed👇). Here is an updated table of high-quality studies assessing VE against infection, including just 3 from the delta era at the bottom
academic.oup.com/ofid/advance-a…
When using regular (or cross-sectional) systematic testing to estimate VE, you are really measuring VE against a composite of infection and duration of PCR-positivity, as highlighted recently by @dylanhmorris.
Fascinating discussion of these methods here sciencedirect.com/science/articl…
Read 4 tweets
Aaron Richterman, MD Profile picture
Aug 11, 2021
This 👇claim arises principally from Israeli data (which is unpublished in any form so will withhold judgment) and from the UK REACT 1 study, rounds 12 & 13. But... is the REACT 1 data likely to be solely explained by delta? 🧵
(study link spiral.imperial.ac.uk/handle/10044/1…)
This is the table in question. You can see VE of a combination of AZ/MRNA vs symptomatic infection was 83% (19-97%) in round 12, but only 59% (23-78%) in round 13. The concern of course is that this drop in VE is due to delta, which had completely taken over by round 13 /2
However, while 100% of the isolates identified in round 13 were delta, 80% in round 12 were also delta (20% were alpha). Any effect of delta on VE should have been partially seen in round 12. /3
Read 7 tweets
Aaron Richterman, MD Profile picture
Jan 12, 2021
Interesting poll. Selection/response bias aside, majority picked a low probability, but 40% still thought there was 10+% prob that vaccines will not substantially prevent transmission. This is why I have become convinced this concern is highly unlikely (borderline implausible) 🧵
1. Data from screening PCR at the time of the 2nd moderna mrna vaccine, showing reductions in asymptomatic PCR positivity. This is before the 2nd dose and if anything will underestimate effect. Will have additional confirmation from unblinding pcr and ab

2. Data from AZ vaccine chadox study is a mess, but they did weekly PCR screening and points in the same direction.
thelancet.com/action/showPdf… Image
Read 27 tweets
Aaron Richterman, MD Profile picture
Dec 19, 2020
Thankful to Singapore for surveillance systems that allow for the detailed studies required to truly assess the relative transmission risk of asymptomatic vs symptomatic cov-2 👇, which they find to be much higher in those who develop symptoms /1

thelancet.com/journals/lance…
couple points:

1. Use of serology to stratify recency infection was a nice addition

2. A better description of asymptomatic definition would be helpful. We go through this thorny issue here👇 @mugecevik @EricMeyerowitz @BogochIsaac @nicolamlow

/2
thelancet.com/journals/lanin…
This is consistent with limited data summarized in several nice recent systematic reviews:

1. Transmission potential appears lower in asymptomatic infection from @nicolamlow and team ncbi.nlm.nih.gov/pmc/articles/P…
/3
Read 6 tweets

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