Birx tempered that good news with some warnings: In a number of places, including Washington, Minneapolis and Chicago, case totals haven’t declined significantly. She hoped to convey the positive changes the country has seen since implementing sweeping measures to control the spread of the virus, but at the same time she had to acknowledge that warning signs remain.
President Trump has repeatedly suggested that the country has moved into a phase where we can generally return to normal, with the government stamping out “embers” of localized outbreaks that flare up. Birx’s presentation suggests that there are still some large uncontained wildfires out there, even as the deadly conflagrations in places like New York City have come under control.
This conversation, though, should be considered in the context of how broadly the virus has already spread. To continue the admittedly tedious forest-fire analogy, in those places that have seen high numbers of infections, it’s theoretically harder for the virus to spread, given that there are now a number of people who are immune to infection. Eventually, the hope is to hit “herd immunity,” when there are so many people who are immune to the virus that embers can’t flare up, since there’s nowhere for the fire to spread. Ideally that will happen because of a vaccine — because the underbrush is cleared away before the fire starts. The more problematic way to hit herd immunity is by having the virus spread broadly, infecting a big chunk of the population who then can’t transmit the virus — by having the underbrush burn.
On Thursday, researchers from Imperial College London released estimates of how widely the virus had likely spread in each state. Nationally, the report estimated that 4.1 percent of the country had probably already been infected, though the likely range of infections was 3.7 percent to 4.5 percent. In 14 states, the virus had spread more broadly, particularly in New York and New Jersey, where it had probably reached more than 16 percent of the population. In an additional 14 states, the researchers estimated that it had reached fewer than 1 in 100 residents.
Given the novelty of the virus, this is probably the full extent of immunity that exists (assuming that those who’ve been infected are now immune, which is still something of an open question). There’s no vaccine that can spread immunity in a more controlled way, just infections and recoveries.
So how close is this to herd immunity? The density of an immune population for determining what might effectively constitute herd immunity ranges from 70 percent to 90 percent. Meaning that, even in New York and New Jersey, we’re not very close.
There are some important qualifiers here. One is that there are places in New York — specifically, the city — where the percentage is higher. Another is that even some immunity might slow the spread of the virus in some places.
That there has been so little relative exposure, despite the million-plus confirmed cases, means there is still plenty of opportunity for the virus to spread. While Trump would like to portray the situation as controlled and largely behind us, and while Birx would like to offer evidence that we’ve at least seen broad improvement, that so many Americans remain at risk to infection means that significant danger persists.
In the past month, all 50 states have taken steps to scale back efforts to contain the virus.