An update on Delta, vaccination protection and viral loads from the aggregate data available, with new @PHE_uk data 1. Delta infections are characterized by very high viral loads (low Cts). When a breakthrough occurs, the load is similar to unvaccinated, but clears more rapidly
3. The totality of the data suggests VE for mRNA vaccines vs Delta infections has been substantially reduced, ~95% vs ancestral strain, now 50-60% vs Delta, particularly noting new REACT data
OTOH VE vs hospitalizations & death is holding up well, > 95% (J&J data today 71%)
4. A new @CDCMMWR report today on Delta outbreak in Mesa County, Colorado has an estimated vaccine effectiveness of 78% (vs symptomatic infection) cdc.gov/mmwr/volumes/7…
Calls for "masking in indoor settings irrespective of vaccination status" in areas of high Delta incidence
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Summary Delta breakthrough studies, Ct/viral load, vaccine effectiveness (VE)
Only 1 large study of Ct/viral load, shows some vaccine reduction
VE ranges 39-88%; it's likely ≤ 60% at best for mRNA
More data needed, but points to need for boosters for at least some people
Overall, these findings certainly are concordant w/ increased Delta breakthrough symptomatic infections we're seeing and a major decline in protection (~95% w/ mRNA) compared with previous strains, as reviewed here
Recall that 1-dose mRNA or AZ had little (30%) efficacy (1st study in Table). All of this reflects Delta's immune evasiveness. We're very lucky it's holding up for reduction of hospitalizations/deaths but this🦠is far more formidable for both transmission and our immune response
T cells were supposed to be the "on-demand" reserves to kick in after the normal decline of neutralizing antibody (nAb) levels, providing protracted protection. But several new reports point to nAbs as key. 1. @NEJM report on breakthroughs w/ low nAbs
T cells were especially supposed to be helpful, relatively unaffected by variants, as this study and others support (pre-Delta) cell.com/action/showPdf…@CellRepMed
The data from Israel, for fully mRNA vaccinated reduced protection vs severe illness from Delta, in age > 60, down from 97% to 81%, is yet unpublished, but has led to a change in policy to offer booster shots for this age group ft.com/content/b6a804… by @MehulAtLarge@FT
If this holds up, it's the first sign of a significant dropdown of protection against hospitalizations and death for these vaccines. I hope all of the data will be shared ASAP as the implications are big.
When this first surfaced last night, I asked my friend @segal_eran about the lack of concordance with the UK @PHE_uk data. Here is our back and forth, with his key points
Why is Canada at 1.4 cases/100,000 people and the US at 20/100,000, heading towards its 4th wave?
Remarkably, Delta prevalence for new infections is 10% vs 93%, respectively.
And yes, there is also an ever-growing gap in vaccination coverage, favoring Canada's ability to defend against Delta as it inevitably rises
Very important @NEJM paper today on breakthrough infections (BTI) post-vaccination in Israeli health care workers.
5 key points: 1. Of ~1500 people, 0.4% had BIs, sequenced to be Alpha 85% (this was pre-Delta) nejm.org/?query=feature…
2. All these BTIs were mild (67%) or without symptoms (33%), done due to routine testing. No hospitalizations.
3. 7 of 36 (19% ) of BTIs had "persistent symptoms" > 6 weeks. Table below
An indicator for the potential of #LongCovid in BTIs in a few of these people at > 6 weeks, but that's a very limited and early time for assessment.