Preliminary results from a statewide random sample indicate that 14 percent of New Yorkers are immune to covid. Assuming the results prove valid and generalizable, what interpretations can be drawn?
Prevalence is high. The running tally of New Yorkers testing positive for the virus stands at 268 thousand. Extrapolating from the immunity study, the actual count would be around 2.7 million — ten times the official rate.
Prevalence isn’t as high as some thought it might be. Two immunity studies recently conducted in California found that the rate of infection might be as much as fifty times as high as the official diagnostic counts. If the CA results had been replicated in NY, the actual statewide prevalence of covid would be 13.4 million, or 70 percent of the state population.
The mortality rate is higher than projected. Early in the pandemic, mortality rate estimates ranged as high as 2 percent; more recent estimates have dropped to around 0.2 percent. To date nearly 50 thousand US deaths have been attributed to covid. If, per the NY study, 9 million Americans have been infected, the mortality rate would be 0.6%.
Some societal implications:
The US is a long way from herd immunity. Coronavirus is highly contagious — on average, newly infected individuals pass the virus on to 2.5 others. Herd immunity can’t be achieved until the contagion rate drops below 1.0, which won’t happen until the virus has infected at least 60 percent of the population. Based on the NY findings, only around 3 percent of the US population has been infected.
The death toll for achieving herd immunity would be sizable. 57% of a total population of 330 million: that’s another 190 million people who need to be infected in order to get the rate of contagion below 1.0. At a mortality rate of 0.6 percent, another 1.15 million would need to die en route to herd immunity. To put that in perspective, the viral body count to date is only 0.05 million people — that’s rounding error.
Individual case tracking is more manageable than previously expected. Eventually an effective vaccine will convey acquired immunity on the herd. That’s at least a year off. Until then, the best alternative strategy for bringing the contagion rate below 1.0 is to isolate newly infected people, as well as their social contacts, from the herd until they recover. For the past three weeks the incidence of newly diagnosed cases has plateaued at around 30K per day: multiply by 10 and you get around 300K new cases daily. That’s a lot of identifying and quarantining and contact tracing; still, it’s far less than the California immunology findings implied. As noted in yesterday’s post, the State of Washington is hiring a brigade of case trackers, estimating that each tracker can keep tabs on 7 new diagnoses and 21 new social contacts per day. At that rate the country would need around 43 thousand case trackers, or a little over 800 per state. 26 million Americans have lost their jobs due to the pandemic; fully staffing a nationwide case-tracker brigade would provide paid and meaningful work to 2% of the newly unemployed.
Some public policy inferences:
The worst is yet to come.
Herd immunity is a worst-case scenario.
Individual case tracking should be diligently implemented.
Prioritize and fast-track the vaccine research.