A New Coronavirus Narrative

Anomalously diverging US covid trends, observed since early May, persisted over the most recent ten-day span. As has been widely reported, official test-positive diagnoses, generally flat over the prior month and a half, soared:

  • June 22 – July 2:   44.5K new test-positives per day
  • June 12 – June 22:   27.1K new test-positives per day
  • June 2 – June 12:   22.0K new test-positives per day
  • May 23 – June 2:   21.8K new test-positives per  day
  • May 13 – May 23:   24.2K new test-positives per day
  • May 3 – May 13:   24.5K new test-positives per day

Meanwhile, covid death rates, which had been on the decline, went up, but only slightly, remaining far lower than they were two months ago:

  • June 22 —  July 2:    630 deaths per day
  • June 12 —  June 22:   599 deaths per day
  • June 2 –  June 12:   853 deaths per day
  • May 23 –  June 2:   940 deaths per  day
  • May 13 –  May 23:   1,316 deaths per day
  • May 3 –  May 13:   1,700 deaths per day

This past month has witnessed frequent reports of dramatic increases in covid hospitalizations, especially from hard-hit states in the South and West. But the latest CDC data, released yesterday, show a continual decline in covid hospitalization rates, from around 3,000 during the first week of May to around 900 during the last week of June — a trend closely paralleling the decline in death rates.

Ten days ago I tentatively attributed the divergence between test-positives and deaths to (1) expanded testing and (2) a shift in clinical practice toward a less severe caseload. These explanations still seem plausible.

Expanded Testing. Throughout the epidemic official covid diagnoses have consistently and grossly underestimated the actual number of new infections. Fauci warned that new cases could soon top 100K per day, but it’s widely agreed that the actual rate of new infections has long exceeded that threshold, with the CDC asserting that the true rate of infection might be ten times higher than the official count. The recent jump in new test-positives might merely be closing the gap between reported and actual numbers rather than chronicling a dramatic increase. The higher number of test-positives reflects in part the expansion of testing beyond the doctor’s offices and hospitals into wider community abatement. According to this June 30 article, testing labs are reaching capacity:

In mid-June, four changes hit all at once, Cohen [Executive Chair of BioReference Laboratories] said. Large companies began to test their employees en masse, hospitals started to test every patient who needed an elective procedure, and nursing homes started regularly testing their employees and some residents. The American public also seemed to seek out voluntary tests in greater numbers this month. The surge in testing overwhelmed both his testing company’s capacity and its equipment suppliers, he said.

Shift toward less severe cases.  As I wrote ten days ago:

More widespread testing in clinical practice brings infected people in for treatment and testing sooner… A reduction in severe cases frees up capacity in doctors’ practices and in hospitals for treating the less severe cases. And let’s not forget the financial incentives: empty schedules and empty beds translate into reduced revenues.

Older people are no more likely to contract the virus, but they are far more likely to get seriously ill and die from it than are younger people. The CDC graph shows that, since early May, the proportion of hospitalized patients 65+ years old has dropped nearly in half (from 46 percent to 28 percent), while the proportion of inpatients aged 18 to 49 has nearly doubled (from 25 percent to 40 percent). So there’s demographic evidence supporting a population-wide downward shift in viral severity.

But while the proportion of younger people being hospitalized has increased over the past two months, the total weekly number of younger hospitalizations has dropped by more than half. The implication is that fewer Americans of all ages are getting severely ill from covid, which further implies that the total number of infections has decreased markedly not just for older people but also for the younger adult sector of the population.

Changing Expectations. Deaths lag behind diagnoses and hospitalizations. It’s still possible that soon the covid hospitalization and death counts will accelerate, paralleling the recent jump in test-positives, and that a viral resurgence in younger adults will again spread to the older demographic, spiking hospitalizations and deaths. But as time goes by it seems likely that a different pattern has already emerged. Older people, recognizing their vulnerability to severe illness, continue to shelter in place, while younger, less vulnerable people go back to work and play. It’s an altered state that seemed inevitable at least a month ago when the country began reopening: young people, let’s get back to business as usual; old people, look out for yourselves.

It’s not clear how much of the abrupt increase in test-positives reflects an actual increase in infections among the younger demographics. The widely cited IHME models estimate that the US infection rate dropped from 240K/day in early April to a current plateau of around 80K/day. What’s really needed is for the Centers for Disease Control to coordinate a systematic national antibody sampling study, repeated at regular intervals, to provide more accurate data on prevalence and contagion and trends. As it stands, epidemiologists are forced to rely on statistical inferences and simulations predicated on spotty and often inaccurate data, the gaps filled by theoretical assumptions that are becoming obsolete. I’ve been using an estimated age-adjusted mortality rate as a back-door proxy for infection rate, but now that the age demographics are shifting downward I’ll have to recalibrate. I’ll get back to that project on another day.

Meanwhile the virus remains widespread and lethal in this country, with the potential for rapidly escalating contagion all too real. Recent press coverage is raising societal awareness of the present dangers faced by the young as well as the old. Some states and cities are slowing the reopening and in some cases partially reversing them; businesses and workers and customers are reluctant to jump back in with both feet.

Tentative forecast. Now that the new patterns of contagion have been established, they’ll likely continue. Official daily diagnoses more closely approximate actual rates of infection which, along with hospitalizations and deaths, will remain remain at levels substantially below the epidemic’s mid-April peak when the old and the comorbid were being hit hardest. Unlike the situation in so many other countries that acted quickly and decisively, the viral spread in the US will not diminish to the vanishing point. The epidemic will keep chugging along, with temporary local bumps and valleys, and with a continually mounting toll on human lives, until an effective vaccine gets rolled out. However, there’s likely enough good sense distributed among the populace to prevent a recurrence of runaway contagion.

 

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