Cross-posted from DT
Interesting article in pre-print (not yet peer reviewed) from the Mayo Clinic comparing Pfizer and Moderna and how they fare over time, including against Delta. It's not peer reviewed yet, but it's also the Mayo Clinic, so I've got a reasonable level of confidence in it. It's important information that's been asked for a lot on these threads, so I'm going to break it down.
Remember though, there is a chance the study won't get published, or will be published with revisions.
This post is going to be a lot of words, but there's a lot to unpack here. Even the TL:DR is long.
TL:DR Both mRNA vaccines are still highly effective against ICU visits and deaths at 6 months. There were no recorded deaths in this group for either vaccine in this study. Pfizer declined hard in July against infections and less against hospitalizations, but continues to prevent ICU visits and deaths at the same rate as Moderna. Pfizer is less effective against Delta than Alpha.
As of July, Moderna confers a 50% risk reduction for overall infection over Pfizer. In Florida, it's a 60% reduction.
There is no statistical difference in ICU visits and no deaths for either vaccine.
Risks are still low overall for fully vaccinated people of either vaccine. The number of breakthroughs is still very low at 326 total so far.
The study ran until July 29, so it does include Delta taking over. Patients from Arizona, Florida, Iowa, Minnesota, and Wisconsin. Not a great cross-section of America, but what we have for now.
https://www.medrxiv.org/content/10.1101/2021.08.06.21261707v2
Breakthroughs were rare, with twice as many occurring in the Pfizer cohort.
They noticed the vaccine effectiveness was declining in April 2021 from Moderna-93% and Pfizer-86% effective to 86% and 76% respectively. So they started collecting data comparing the vaccines against one another in Feb 2021.
July arrived and so did Delta.
They noticed a much bigger decline, especially for Pfizer, correlated with Delta's arrival in force. Correlation doesn't necessarily imply causation and they can't yet say if the increased infections are due to Delta evading the vaccine, or declining immunity, though they do show that Pfizer is more effective against Alpha than it is against Delta.
July 2021 effectiveness against infection
July comparison
They speculate the same reasons for Moderna being more effective that have been speculated by myself and others on here (larger doses and longer dosing interval), but also note the lipids used to coat the spike protein are different.
Unfortunately, they didn't analyze date of vaccination, so it's not clear if it's waning immunity, or Delta, or something else. I think it's likely it's both, but that's my own opinion.
They do find that Pfizer is less effective at preventing symptomatic infection against Delta, than it was against Alpha, though still highly effective.