Preprint out of the UK

Impact of Delta on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK
https://www.ndm.ox.ac.uk/files/coronavirus/covid-19-infection-survey/finalfinalcombinedve20210816.pdf

Findings from the abstract

• The effectiveness of BNT162b2 (Pfizer) and ChAd0x1 (Astrazeneca) against any infections (new PCR positives) and infections with symptoms or high viral burden is reduced with the Delta variant.
• A single dose of the (Moderna) vaccine had similar or greater effectiveness compared to a single dose of (Pfizer) or (Astrazeneca).
• Effectiveness of two doses remains at least as great as protection afforded by prior natural infection.
• The dynamics of immunity following second doses differed significantly between (Pfizer) and (Astrazeneca), with greater initial effectiveness against new PCR-positives but faster declines in protection against high viral burden and symptomatic infection with (Pfizer).
• There was no evidence that effectiveness varied by dosing interval, but protection was higher among those vaccinated following a prior infection and younger adults.
• With Delta, infections occurring following two vaccinations had similar peak viral burden to those in unvaccinated individuals.
• SARS-CoV-2 vaccination still reduces new infections, but effectiveness and attenuation of peak viral burden are reduced with Delta.

This was a big community surveillance study where instead of waiting for people to show up for treatment, they test people independently of symptoms or vaccination status. This helps against some bias (like people not going to the doc for mild symptoms).

Pfizer and Astrazeneca both reduce the risk of new infection even against delta.

Pfizer held up better than Astrazeneca against delta, though both are reduced.

According to this paper, two doses of Astrazeneca is similar protection as previous natural infection.

The Pfizer vaccine protection declines over time.

Pfizer and Astrazeneca both protect against severe disease. Maybe because the vaccines don't protect so well against a local infection (like in your nose) but they do protect against systemic infection (your whole body). Local is more about preventing infection and transmission, but systemic is more about preventing disease.

Lots of virus in vaccinated people, but maybe those viruses are non viable and maybe that peak load doesn't last as long - so not clear how this relates to transmission rates.

If you've been infected after vaccination you are like superman.


Also this study "...argues for vaccinating as many of the population as possible, since those not vaccinated may not be protected by as substantial reductions in transmission among the immunised population as seen other infections, making herd immunity likely unachievable for emerging variants and requiring efforts to protect individuals themselves."

I'm assuming if you've had COVID -- and then were fully vaccinated -- you're pretty bulletproof, too?

I work for an Infectious Disease doctor and that is exactly what he is saying. Actually having Covid, and then getting the vaccines at a later time provides the best protection of all. Better than just having had Covid or just being vaccinated.

Proof is hard to come by.

This study is maybe better because it's random surveillance rather than only looking at people who present for care.

One study really isn't validation one way or another. A body of studies that generally conclude the same thing is how understanding develops. Think of it like a scatter plot but with scientific reports.

They're different. Israel found that among people who showed up for medical treatment and got tested, fewer were previously infected vs vaccinated.

This study randomly tested a ton of people. Different method, different results.

And kudos to Zobel for continuing to bring the data for those who really want to evaluate it and make rational decisions.