Epidemiologists are holding our breath to see how we fare against Delta. We did relatively well with Alpha (well, at least those of us not in Michigan or Oregon), but Delta (and the timing of Delta given pandemic fatigue) is another beast. We aren’t optimistic for a few reasons…
Immunity Wall
Vermont is the clear leader with 66.1% of the population fully vaccinated, Massachusetts (62.2 %) and Maine (61.9%) closely follow. Yes, population size has something to do with their success, but 19 other states have also administered enough shots to cover at more than 50% of their population.
And the vaccines are working. Yesterday we saw even more data from Canada and the UK that confirmed effectiveness against Delta. There is some conflicting data coming from Israel, as one study showed a Pfizer efficacy rate of 64%. But, even this study found that Pfizer still protected amazingly from severe disease.
Unfortunately, some states like Mississippi (29.9%), Alabama (33.0 %), and Arkansas (34.6 %) have a very small proportion of their population vaccinated. Although there are problems with the “natural immunity” strategy, there is some level of protection in these states.
As requested, I updated my graph from last month to show the states’ progress towards “herd immunity”. My estimates have a lot of flaws (see more here), but it’s a decent guesstimate of the immunity wall.
Briefly, this graph takes into account: 1) under-reporting of asymptomatic cases (multiply cases by 3); 2) reinfection rate among naturally infected (20% of naturally infected not protected); and 3) efficacy of vaccines (90% of full vaccinated). This time around I also tried to take into account the rate in which previously infected get vaccinated (60%) given some recent vaccine hesitancy data.
Delta
Unfortunately our U.S. genomic surveillance is suboptimal, making our estimates of Delta delayed and a really rough. Three weeks ago, CDC reported that 51.7% of cases nationwide were Delta. Interestingly, Delta greatly varies by state for now. Some states (like Missouri) have a 90% prevalence of Delta while others have 30%. With a doubling rate of 10 days, this means that today Delta is dominant in many parts of the United States.
And with the high prevalence of Delta is coming an increase in cases. We see this today in Missouri (16 daily cases per 100,000), Nevada (13 per 100,000), Arkansas (12 per 100,000), and Florida (10 per 100,000). Other states are quickly accelerating too, like South Carolina (+145%), Nebraska (+137%), and Mississippi (+44%). These increases are so strong that the national average stopped decelerating and is now plateauing.
A really high wall is needed
We know a really high wall is needed to block Delta. Even the U.K. and Israel, two of the global leaders in vaccinations (67% and 65% fully vaccinated), don’t have a high enough wall for symptomatic or severe disease from Delta. This means not even our high vaccination states (like Vermont) are fully protected.
In the UK, cases continue to increase among unvaccinated and partially vaccinated. Hospitalizations are also starting to increase with the typical a lag time of ~ 3 weeks.
Thankfully Israel cases have stopped accelerating in the past few days. This is probably due to a lot of reasons:
They did not implement a delayed second dose policy like the UK.
Israel has only used mRNA vaccines (which are more efficacious than AstraZeneca)
They’ve had less time with Delta (and so it’s too early to see an increase)
Bottom Line
This pandemic is not over. Many of us are worried about our immunity wall against Delta. Only time will tell how this plays out. TBD.
Love, YLE