Here's What the Delta Variant Has In Store for Low-Vax States

 

Recently I blogged about the nastiness of the Delta variant (first detected in India). At the time it was just getting a foothold in the U.S. but was causing problems in the highly vaccinated UK.

Now it's doing the same in another highly vaccinated country, Israel. The Wall Street Journal just reported that in that country half of infections with Delta are among vaccinated adults.

The WHO has recommended that fully vaccinated adults continue to wear masks because of the variant. Delta is also continuing to increase prevalence in the U.S., and President Biden has emphasized its danger to unvaccinated people.  

Existing vaccines are effective against Delta. However, no vaccine is 100% effective and there are going to be so-called "breakthrough" cases. Though some of those people (about 1% according to a report I saw) will die, infections in vaccinated people are mostly mild or asymptomatic. That's good for the smart people who got vaccinated, but they can still spread the virus to unvaccinated or otherwise vulnerable people.

U.S. Impact

To quantify the impact in the U.S., I got data over the last month from GISAID on the total number of sequences and the number of those with the lineage B.1.617.2 (which is Delta) for each state. This allowed me to calculate a percentage of sequences with the Delta variant for each state.

The average over all states was 14.3%. I recall that about a week ago news outlets pegged the same rate at 10%. So, it's increasing rapidly nationwide.  

In Arizona, the number is 12.25%.  On June 18, when I last checked, the Arizona number was 6.86%.  We are still below the national average but increasing at a higher pace.

Here is what it looks like for the whole country (I kept the maps small so you could see two on the screen at once):

In general, the states with the highest percentage of Delta sequences also have the greatest number of new cases (data from the CDC API):

Though there are some exceptions, they also tend to have low vaccinations rates (data from JHU):

Using the data behind these maps, I did an analysis called multiple regression to see how Delta% and vaccinated% are related to new cases. Both have a statistically significant (i.e., non-chance) effect on new cases, and together they explain about 37% of the variation among the states in new cases.  

For every 1% increase in Delta% there is an 0.077 increase in new cases per 100K 7-day average. For every 1% increase in vaccinated%, there is a 0.124 decrease in the new cases figure.

So, if these numbers represent ongoing trends, the good news is that vaccination is almost twice as effective a preventing new cases as Delta is at causing them. The bad news is that there are still a lot of unvaccinated people. They're going to get hit hard by a much more infectious bug, and vaccination efforts are stalling in the low-percent states (including Arizona).

Missouri is a case in point and a warning for State 48. They have slightly fewer people vaccinated (35%) than here (37%) but are in the same ballpark.  

But 64% of their sequences are Delta (vs. 12% here), and they currently have the highest case rate in the country at 12.31 per 100K 7-day average. I predict that's where we will be in a couple weeks if steps aren't taken to get more people jabbed, and quick.

Image by Corona-zona