Very pleased to share @PHABlabumd’s latest work, “Exhaled Breath Aerosol Shedding of Highly Transmissible Versus Prior SARS-CoV-2 Variants” published online, ahead of print in @CIDJournal!
A co-🧵 by @Jianyu16 and @drkristenkc…
academic.oup.com/cid/advance-ar…
A co-🧵 by @Jianyu16 and @drkristenkc…
academic.oup.com/cid/advance-ar…
Curious about viral aerosol shedding patterns of SARS2 over the first 2 years of the COVID pandemic? This 🧵 is for you!
Here, we 1) measured the infectivity and rate of SARS2 shedding into exhaled breath aerosol (EBA) by COVID+ volunteers during the Delta and Omicron waves, and
Here, we 1) measured the infectivity and rate of SARS2 shedding into exhaled breath aerosol (EBA) by COVID+ volunteers during the Delta and Omicron waves, and
2) compared those rates with those of prior SARS2 variants from our previously published data (Adenaiye et al, 2021) collected June 2020 through April 2021.👇🏻
academic.oup.com/cid/article/75…
academic.oup.com/cid/article/75…
We also,
3) compared viral EBA shedding rates among Omicron subvariants (BA.1, BA.1.1, and BA.2), and finally
4) examined associations of viral aerosol shedding with upper respiratory viral load, vaccination, serology, demographic, and clinical predictors.
3) compared viral EBA shedding rates among Omicron subvariants (BA.1, BA.1.1, and BA.2), and finally
4) examined associations of viral aerosol shedding with upper respiratory viral load, vaccination, serology, demographic, and clinical predictors.
From June 2020 – March 2022, we used the Gesundheit-II machine to collect and measure viral load in EBA of 93 COVID+ volunteers recruited from the @UofMaryland, College Park and surrounding community.
Age range: 6 to 66 years
Yay for all participants, especially the kiddos!
Age range: 6 to 66 years
Yay for all participants, especially the kiddos!
Participants were mildly symptomatic (97%) or asymptomatic (3%) at the time of sampling.
Here’s a simple breakdown of the study population by variant and vaccination status:
Here’s a simple breakdown of the study population by variant and vaccination status:
To provide exhaled breath aerosol samples, participants placed their head in the G-II cone for 30 minutes. At 3 time intervals, they sang “Happy Birthday” then shouted “Go Terps!” thirty times. twitter.com/i/web/status/1…
We also collected saliva, mid-turbinate swabs (MTS), and mobile phone swab samples for RT-PCR and virus culture, as well as blood samples for serology.
Among Delta & Omicron cases, we detected SARS2 RNA in saliva, MTS, aerosol, and phone swab samples.
We recovered infectious (culture+) virus from all sample types (saliva, MTS, aerosol) except phone swabs.
We recovered infectious (culture+) virus from all sample types (saliva, MTS, aerosol) except phone swabs.
Most (21/32) Delta and Omicron cases shed detectable viral RNA concentrations in exhaled breath aerosol.
Viral RNA loads were on average 5x greater in the fine (≤5 μm) aerosol size fraction than in the coarse (>5 μm) aerosol size fraction.
Viral RNA loads were on average 5x greater in the fine (≤5 μm) aerosol size fraction than in the coarse (>5 μm) aerosol size fraction.
Infectious SARS2 was recovered from the exhaled breath aerosol of one boosted (Omicron BA.1.1) and three fully vaccinated (two Delta, one Omicron BA.1.1) cases.
Credit to @MattFrieman’s lab for doing the culture work!
Credit to @MattFrieman’s lab for doing the culture work!
One of the culture+ EBA samples was from the coarse aerosol size fraction, while the remaining three culture+ EBA samples were from the fine aerosol size fraction.
The culture+ coarse EBA sample was from a Delta case.
The culture+ coarse EBA sample was from a Delta case.
We observed no significant difference in viral aerosol shedding rates between Omicron BA.1, BA.1.1, and BA.2. Thus, it is still unclear why BA.2 was seemingly more transmissible than BA.1.
https://twitter.com/drkristenkc/status/1553879815651991553
Now let’s look at all the data from the first two years of the pandemic (not just Delta & Omicron waves).
Fine EBA viral RNA loads from Omicron cases were, on average, similar to those from Alpha and Delta cases.
Fine EBA viral RNA loads from Omicron cases were, on average, similar to those from Alpha and Delta cases.
Compared w/ SARS2 ancestral strains & variants not associated with increased transmissibility, viral EBA shedding was significantly greater during infections w/ Alpha, Delta, and Omicron
Fig 2. Viral RNA copies in EBA by variant over time
Each data point = one 30-min EBA sample twitter.com/i/web/status/1…
Fig 2. Viral RNA copies in EBA by variant over time
Each data point = one 30-min EBA sample twitter.com/i/web/status/1…
This suggests that the 3 highly transmissible variants of concern (Alpha, Delta, and Omicron) independently evolved a high viral aerosol shedding phenotype, demonstrating convergent evolution.
This is likely the best human subject research data we have on how emerging viruses can adapt to shed/transmit more efficiently via aerosols. Such viral adaptation should be expected but we seem to lack this foresight (and evidence) when preparing for and controlling pandemics.
Although rates of shedding between Alpha, Delta, and Omicron did not differ significantly, the highest shedder was an Omicron case that shed 3 orders of magnitude more viral RNA copies than the max observed for Delta and Alpha.
Let’s take a look at the relationship between viral RNA loads in fine EBA and MTS/Saliva.
When looking at Omicron (Fig 3 plot b) we see that the highest viral RNA loads in EBA are associated w/ much lower viral loads in MTS when compared w/ all other variants (plot a).
When looking at Omicron (Fig 3 plot b) we see that the highest viral RNA loads in EBA are associated w/ much lower viral loads in MTS when compared w/ all other variants (plot a).
We also see a clear shift toward saliva viral load (plot c and d) being a stronger predictor of viral RNA load in EBA for Omicron (BA.1, BA.2).
Over the pandemic, 3 highly transmissible variants (Alpha, Delta, Omicron), as well as higher systemic symptom score, saliva viral RNA load, age, and # of coughs per 30-min sampling session were sig predictors for higher fine EBA viral RNA load in an age & sex adjusted model.
Days post-symptom onset was not a sig predictor of viral RNA load in EBA in our study.
Having received a vaccine booster dose prior to infection was associated with shedding more viral RNA in coarse EBA, but it was not associated with fine or total EBA viral RNA load.
Having received a vaccine booster dose prior to infection was associated with shedding more viral RNA in coarse EBA, but it was not associated with fine or total EBA viral RNA load.
Five Omicron cases had evidence of a recent prior infection (they were sero-positive for anti-nucleocapsid (anti-N) IgG at enrollment, one to six days post-symptom onset). Virus was detected in their MTS, albeit in sig lower quantities compared to those neg for anti-N IgG.
The five anti-N IgG sero-positive cases were the only participants with culture-negative virus in MTS
*None of them shed virus in aerosols*
This suggests that having had a recent prior infection may reduce/eliminate one’s contagiousness during an Omicron breakthrough infection.
*None of them shed virus in aerosols*
This suggests that having had a recent prior infection may reduce/eliminate one’s contagiousness during an Omicron breakthrough infection.
In conclusion, COVID cases can shed infectious viral aerosols even when fully vaccinated/boosted. Evolutionary selection appears to favor variants associated w/ high viral aerosol shedding. Combo of immune evasion & high viral aerosol shedding likely responsible for Omicron’s 🚀
Our data are consistent with a dominant role for airborne transmission (aerosol inhalation regardless of distance from infector) in the spread of COVID-19.
We need a vaccines + air cleaning strategy to adequately control COVID.
We need a vaccines + air cleaning strategy to adequately control COVID.
Let’s get it done! @WHCOVIDResponse @CDCgov
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