Missouri leading the way with Delta cases.

Missouri is currently leading the US in per capita covid cases, with the increase driven by delta cases.

Looking at the graph, you can see that delta is now growing much faster in MO than in CA, even though back in April/May these states had about the same number of delta cases relative to population size. The dashed lines represent delta and solid lines alpha.

However, the recent rate of increase in MO is still less than half the rate in the UK. That doesn't mean that we shouldn't keep encouraging people to get vaccinated. If a variant is increasing in case numbers over time, that means that we are below herd immunity for that variant.

When I look at the map of Missouri, the new cases are mostly showing up in the Springfield area, which has an unfortunate combination of both low vaccination rates and low prior case numbers relative to the national average. California has below average prior cases, but above average vaccination rates.

It's important to realize that both CA and MO are apparently below herd immunity for delta. It's just that CA is closer to it, and therefore it will take fewer vaccinations or cases to get there.

I'm still not entirely sure what is going on with the UK. Part of it is probably that the delta variant is being passed around in social circles of young people with low vaccination rates. Something else I didn't realize until someone provided a link on a previous post is that the majority of the vaccinated population in the UK received the AZ vaccine. So while their overall vaccination numbers are slightly better than the US, the level of resistance to infection is going to be lower.

In a recent report out of the UK, the Pfizer vaccine was 88% effective and the AZ vaccine was 60% effective against symptomatic covid. Both have more than 90% efficacy against hospitalization for covid, but Pfizer is much better at preventing infection. Going all the way back to the early challenge trials in monkeys, Pfizer reduced the amount of virus that could grow in the upper respiratory tract, but AZ only reduced virus in the lungs. Because virus in the upper respiratory tract is more easily transmitted to the outside world, AZ would theoretically be less able to reduce transmission than is Pfizer.

Out of 60K delta cases in the UK, 4K have been in fully vaccinated people, 36K in totally unvaccinated people, and 13K in people with just one shot. The remaining 7K are in people with unknown vaccination status. So the main driver is the unvaccinated population, but there is a not insignificant partially vaccinated component. It's also possible that vaccinated people are having asymptomatic cases and spreading the virus around without being detected.

All of that is still just speculative. Fortunately, the UK is good at data collection and is keeping a close eye on the situation.

Cases by county in the US:
https://coronavirus.jhu.edu/us-map

Majority of vaccines in the UK are AZ:
https://www.gov.uk/government/publications/coronavirus-covid-19-vaccine-adverse-reactions/coronavirus-vaccine-summary-of-yellow-card-reporting

Most recent UK report:
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/994839/Variants_of_Concern_VOC_Technical_Briefing_16.pdf

Vaccine map of MO:https://data.news-leader.com/covid-19-vaccine-tracker/missouri/29/