The story is a little more complicated than “stay 6 feet away” guidelines. Coronavirus risk is simply not one-dimensional. We need to discuss high-risk activities & environments. I spoke w @B_resnick & discussed 4 dimensions of transmission risk #COVID19
We need to think about risk in four dimensions: distance to other people, environment, activity, and time spent together.
A crowded indoor place, with poor ventilation, filled with people talking, shouting, or singing for hours on end will be the riskiest scenario. A sparsely populated indoor space with open windows is less risky (but not completely safe).
On the other end of the spectrum running quickly past another jogger outside is minimal risk. There are many scenarios in between. In general, outdoors is lower risk. But if you have a gathering outside, and you spent all day together with your friends, risk is still higher.
And it’s not just the location or the time spent together: The activity people are engaged in matters, too.
In Washington state, a person with the virus attended a choir practice, and more than half of the other singers subsequently got sick. This was labeled a “superspreading” event, as one infection led to 32 others. Why was this so risky?
The convergence of many risk factors: singing, the time spent together (the practice was 2.5 hours), and the interaction between the choir members in an enclosed space (not only did they all practice together, they also split up into smaller groups and shared cookies and tea).
That’s why we need to think of risk in terms of many dimensions: so we can each think critically and not fall back on rules that are too simplified.
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Very interesting analyses about the virology of #Omicron, which may explain the faster spread of this variant.
According to a new lab study, Omicron infects & multiplies ~70x faster than the Delta variant and the wild type SARS-CoV-2 in the human bronchus, but not in the lung.
In this ex vivo study (press release), Michael Chan, Malik Peiris & John Nicholls et al. @hkumed show that at 24h after infection Omicron replicated ~70x faster than Delta in bronchus. Interestingly, it replicated ~10x less efficiently in the lung tissue. hkumed.hk/96b127/
Another analysis by @BalazsLab also supports these findings. In this lab study w/ pseudoviruses, Omicron showed greater ability to infect cells than other variants, which was ~ 4 times more infectious than the original strain, also more than Delta. medrxiv.org/content/10.110…
This is a live virus neutralisation assay. Neutralisation studies can tell us whether levels of Ab in the blood (convalescent and vaccinated plasma) are high enough to prevent the virus from infecting cells in the lab.
.@sigallab & colleagues tested plasma from those who received vax only (orange) & those who had vax + previous infection (green) and showed a significant (~40x) decline in neutralisation activity, but this was not a complete escape & reduction was less in hybrid anti-sera.
🦠 There’s a lot we don’t yet understand about Omicron, including its impact on immunity and what it means for vaccines. New data will be emerging over the next few wks, which could be misinterpreted w/o context. What we might expect & how to interpret the emerging data? 🧵(1/n)
1- Genomic data:
The biggest concern with omicron is that it contains >30 mutations in just the spike protein, the part which helps it enter human cells and the target for vaccines. This mutation profile is very different than other VOCs. (2/n)
There are plausible biological consequences of some of these mutations, but we don't really know the combined effect of all these mutations, so full significance of omicron is uncertain.
There is a lot of concern/confusion about vaccine effectiveness against the delta variant. How effective are the vaccines against Delta & how to interpret real-world observational data? So much misinformation is being circulated, so this thread brings key data together. 🧵(1/n)
Vaccine efficacy measures the relative reduction in infection/disease for the vaccinated vs unvaccinated arm. For instance, a vaccine that eliminates all risk would have an efficacy of 100%. Efficacy of 50% means you have a 50% reduced risk compared to an unvaxxed person. (2/n)
All studies assessing the performance of vaccines against Delta are based on real-world data (vaccine effectiveness), which are influenced by variant transmissibility, human behaviour, and immunity status of the population, therefore they require careful interpretation. (3/n)
There is a lot of confusion about the efficacy of AstraZeneca/ChAdOx1 vaccine against COVID19 due to B.1.351 / 501Y.V2 - summarising the results of phase 1b/2a double-blind randomized trial conducted in South Africa (based on @GovernmentZA press conference).🧵(1/6)
Adults aged 18-65 years without severe comorbidities and HIV were recruited. It was designed to show >60% efficacy against symptomatic disease, but because only 2000 participants were recruited with 42 total events, this analysis was not statistically powered. (2/6)
In total, 1749 participants were recruited, the population enrolled was young and generally healthy; the prevalence of hypertension, respiratory disease, and diabetes was low. Therefore, it was not designed to assess efficacy against severe disease. (3/6)
Concerns about outdoor transmission risk seem to be trending again. What is the risk of transmission outdoors and should we be more worried about outdoors with the new more-transmissible variant? 🧵(1/n)
The risk of transmission is complex and multi-dimensional. It depends on many factors: contact pattern (duration, proximity, activity), individual factors, environment (e.g. outdoor, indoor), socioeconomic factors, and mitigation measures in place. (2/n)(gov.uk/government/pub…\)
Transmission is facilitated by close proximity, prolonged contact, and frequency of contacts. So, the longer the time you spend with an infected person and the larger the gathering, the higher the risk is. (3/n) (academic.oup.com/cid/advance-ar…\)