Cuomo has reported that a survey conducted from May 1 through June 13 found 21.6% of New York City residents tested to have the antibodies. There’s no scientific-paper version available yet, so I took the liberty of adjusting that up to an estimated prevalence of 24.3% using the same formula as the Annals of Epidemiology paper, in part to avoid describing a situation in which the number of people of who have had Covid-19 in the city went down over time. I wouldn’t count on that being exactly right, though, and it’s even possible that antibody prevalence is declining in New York, warned Eli Rosenberg, the University at Albany epidemiologist who was lead author of the Annals of Epidemiology paper. New research emerging from China, Spain, the U.K. and the U.S. indicates that antibody levels can fall quickly in people with mild and asymptomatic cases of Covid-19. “This news is going to (and is starting to) rock the world of us folks who are conducting COVID-19 population surveys,” he emailed.
So yes, these antibody-survey-based estimates are provisional and imperfect! So is the rest of our knowledge about Covid-19, though, and the disappearing-antibodies effect shouldn’t have too big an impact on the numbers from this winter and spring.
The simplest way to use these numbers to estimate exactly when people became infected with Covid-19 is to calculate backward from the data on deaths. I estimated a fatality rate of 0.98% from the antibody prevalence estimated in the Annals of Epidemiology article and the city’s estimate of the Covid-19 death toll (both confirmed and suspected cases) at the end of April, then assumed that infections occurred an average of 19 days before deaths did.
One View Of The Epidemic
The CDC estimates that the median time from infection with the coronavirus to death is 18 days for those 65 and older and 21 days for everyone else. Three-quarters of Covid-19 deaths in New York City have been among those 65 and older, which is why I went with 19. This may understate the early spread of the disease, though, because it was probably concentrated among younger people who had just been to Europe or hung out with those who had, and were more likely than senior citizens to be spending lots of time in crowded bars, concerts, dance clubs, restaurants, offices and subways. So I also charted the disease’s possible course through the city’s population using the Covid-19 Scenarios tool put together by researchers in the laboratory of physicist-turned-epidemiologist Richard Neher of the University of Basel in Switzerland (and some other people).
Covid-19 Scenarios consists of a Susceptible-Exposed-Infected-Recovered model of disease spread that allows you to tweak parameters such as the reproduction number and the period of infectiousness, as well as impose interventions that slow transmission. These interventions are not specific actions such as school closures; you simply put in an intervention for a period of time and estimate for yourself how much it will reduce transmission. My goal was to construct a scenario in which the epidemic began in early February and cumulative infections at various dates were near those estimated from Mount Sinai’s April samples and the state surveys. After some experimenting I decided to construct multiple scenarios, because designing an epidemic that hit all of the weekly Mount Sinai targets proved too difficult.
These are admittedly some pretty crazy-looking epidemics. “It looks to me that in your scenario the outbreak is coming down a little too fast,” Neher emailed in critique of one of my early efforts, and I was never able to fix that entirely.
How Things May Have Played Out In NYC
As a New York City resident, I can testify that the Covid-19 epidemic was at its most awful and frightening here in late March and early April. If my estimates are even close to right, though, the epidemic peaked sometime in mid-March and was rapidly declining as all New Yorkers who could holed up at home and freaked out. In other words, the holing-up and freaking-out seems like it actually worked — and it’s too bad we didn’t do it a little sooner.
When The Tide May Have Turned In March
The now-infamous March 2 tweet from New York City Mayor Bill de Blasio exhorting New Yorkers to “go on with your lives + get out on the town despite Coronavirus” came on the same day that his San Francisco counterpart, London Breed, was warning the city’s residents to “prepare for possible disruption from an outbreak.” Over the course of the next few days, West Coast-based tech companies also began encouraging employees to work from home. That may have had some modest effect in New York, but such policies didn’t become the default here until the week of March 16, which is also when public schools closed and restaurants all over the metropolitan area were forced to go takeout-only. Governor Cuomo’s subsequent order closing all nonessential businesses and urging residents to stay home was issued on March 20 and took effect March 22. The nursing home order referred to in the chart was a directive from Cuomo barring the facilities from rejecting recovering Covid patients that has since been the subject of much criticism, some of it implying that the decision was largely responsible for the state’s highest-in-the-nation Covid-19 death toll.