Thread by @sailorrooscout

I figured it was best to make a comprehensive thread concerning the study out of The Lancet concerning variant B.1.617.2 (Delta) after mRNA vaccination to help clear up some confusion. Most aren’t breaking it down into layman’s terms, so allow me. Let’s discuss.

Firstly, 250 people, one study, one assay. Median age was 42, fairly healthy. We have established the evasiveness of B.1.617.2 is similar to B.1.351. Got it? Okay, good. I’ll make this simple and put it into bullet points. Study can be found here: thelancet.com/journals/lance…

•One dose is not enough, two are needed for high levels of nAbs. Yes, we knew this. It also falls in line with PHE data from last week
•EXTREMELY IMPORTANT TO NOTE: Antibody neutralization is NOT the same as vaccine efficacy, as in a 5.8-fold reduction in antibody

neutralization does NOT mean the same thing for vaccine efficacy!
•This study showed a 2.2-fold reduction in neutralization for variant B.1.617.2 (Delta) relative to variant B.1.1.7 (Alpha) (5.9 / 2.6)
•PHE data so far shows a ~10% drop in vaccine efficacy for variant B.1.617.2

(Delta) compared to B.1.1.7 (Alpha) after two doses of Pfizer- see how different that is when we look at it on a different scale? It’s important to know this. Let’s go further.
•Yes, remember initial antibodies from the vaccines DO wane with time! This study doesn’t take into

account T-cells/cell-mediated immunity. Remember, when initial vaccine induced antibodies wane, your immune system will kick in and make more when it needs to when you’re exposed to the virus
•Erosion of antibody neutralization (due to age, time since your dose, etc.) is likely

to produce a larger drop in vaccine efficacy for an already-evasive variant more so than for a less evasive one- yes, we knew this too, hence the need for boosters this autumn for the elderly/most-at risk. I have stated this numerous times. Why is this? Because initial nAbs help

prevent infection BUT is not a sole indicator of vaccine effectiveness (please keep that in mind). Lower levels of antibodies can still protect against the virus but for the most vulnerable who can’t fight an infection as easy as some of the rest of us, boosters are recommended-

as TCRs kick in after you’re exposed again. Side note- a really good study on this point: SARS-CoV-2-specific memory B-cells can persist in the elderly despite loss of neutralizing antibodies in case you fancy some more reading. Let’s continue.
biorxiv.org/content/10.110…

•It IS normal for initial antibody titers to drop over time. Yes, it happens! What matters is how quickly memory cells kick back in to mount a secondary response upon next exposure as I said above. For the vulnerable/elderly, this drop might happen faster and therefore that’s-

why a booster is heavily needed (the authors even addressed this)
•That second dose is very much so needed- the study highlights this too! The need to consider minimizing the gap between doses to provide protection faster is important- last time I checked second doses were

being surged and given earlier which is exactly what should be done to help mitigate spread
•Real-world data is pertinent right now. See the hospitalizations amongst the fully vaccinated. They’re LOW. Indeed the vaccines ARE working. See:

https://twitter.com/sailorrooscout/status/1400535174824214533

Going to add this here for an idea of vaccine effectiveness: 73% of B.1.617.2 cases are in unvaccinated individuals. Only 3.7% of B.1.617.2 cases are in individuals who’ve had both doses according to the report from PHE yesterday. See Table 4 Page 12 assets.publishing.service.gov.uk/government/upl…

The author of the study: “vaccine rollout has been a huge success in the UK, slow and steady has almost won the race, B.1.617.2 makes it a bit more uphill as we near the finish line. Two doses as quickly as supply allows, monitor Ab levels, boost those who need.” That’s a wrap.