An Omicron paradox -- UPDATED

Last update: Monday 1/3/22

A recent op ed in the NY Times suggested that given Omicron's rapid conquest of the United Kingdom, a highly vaccinated country, it was better to make pandemic management policies based on surges in hospitalizations, rather than surges in infections. The ultimate objective has always been to keep hospitals (and other treatment facilities) from being overloaded. 

For previous variants, including Delta, rising or falling infections were reliable predictors of rising or falling hospitalizations. By contrast, surging infections by Omicron don't seem to be reliable predictors of surging hospitalizations.

• "Why Hospitalizations Are Now a Better Indicator of Covid’s Impact", Monica Gandhi and Leslie Bienen, NY Times, 12/11/21 
• "Omicron’s impact better measured by rising hospitalizations than cases, Fauci says", Bryan Pietsch and Jennifer Hassan, Washington Post, 1/3/21

As of this writing, Omicron seems to differ from Delta in three ways: 

• First, Omicron produces far more breakthroughs than Delta. Indeed, its behavior suggests that we should expand the notion of breakthroughs. A Delta breakthrough occurred when a vaccinated person become infected by Delta.  However, Omicron seems to be noticeably more effective than Delta in re-infecting unvaccinated persons who had recovered from prior infection.
  
  So Omicron can prey upon a more diverse pool of potential victims than Delta = unvaccinated persons who have never been infected + infected unvaccinated persons who have recovered + vaccinated persons .
  
  
• Second, Omicron seems to be far more transmissible than Delta, perhaps two or three times as transmissible. In other words, during the time it might take Delta to infect 100,000 victims, Omicron might infect 200,000 or 300,000
  
  -- "Omicron is spreading more than twice as quickly as the Delta variant in South Africa, scientists report.", NY Times, 12/3/21
  -- "Omicron spreading rapidly in U.S. and could bring punishing wave as soon as January, CDC warns", Lena H. Sun, Joel Achenbach, Laurie McGinley and Tyler Pager, Washingtpn Post, 12/15/21 
  
  
  
• Third, data available so far suggests that Omicron is not as lethal as Delta, i.e, a smaller number of Omicron victims have required hospitalization per 100,000 persons infected by Omicron than would have been hospitalized had they been infected by Delta. So large surges in Omicron infections might not be followed by large surges in hospitalizations and deaths, especially if the the lion's share of the infections were asymptomatic or mild.
  
  -- "Omicron Infections Seem to Be Milder, Three Research Teams Report", Carl Zimmer and Emily Anthes, NY Times, 12/22/21
  -- United Kingdom, "People with Omicron are less likely to need hospitalization.", Marc Santora and Adeel Hassan, NY Times, 12/31/21 
  -- South Africa, "Omicron has passed peak in South Africa, causing relatively few deaths and hospitalizations, authorities say", Amy Cheng, Washington Post, 12/31/21

Although Omicron may not be as lethal as Delta, a paradox can be detected in the surge in hospitalizations now predicted by the United Kingdom (UK). According to the NY Times, the UK is a highly vaccinated nation (70 percent fully vaccinated), more so than the U.S. (61 percent). Although most of the initial victims of Omicron have been asymptomatic or mild, the UK Prime Ministers is predicting that a "tidal wave" of severely ill cases will soon overwhelm the U.K.'s hospitals unless everyone receives booster shots asap. How is this possible if Omicron is not as lethal as Delta, the variant that was predominant in the U.K until the sudden emergence of Omicron a few weeks ago?

• "UK's Johnson warns of Omicron 'tidal wave', says two doses not enough", Andy Bruce and Kate Holton, Reuters, 12/10/21
  
  
• United Kingdom, "U.K., With Surging Cases, Is on ‘War Footing’ Against Virus", Megan Specia, NY Times, 12/20/21 

As per the following article in the NY Times, seventy-five percent of the people who died from the virus in the United States — or about 600,000 of the nearly 800,000 who have perished so far — have been 65 or older. One out of every 100 adults over 65 died from covid, but only 1 of every 1400 U.S. adults under 65 died. Indeed, three-quarters of U.S. Covid deaths have been among people 65 and older. Accordingly, we should focus our concerns about Omicron on older residents.

• "As U.S. Nears 800,000 Virus Deaths, 1 of Every 100 Older Americans Has Perished", Julie Bosman, Amy Harmon and Albert Sun, NY Times, 12/11/21  

Recent findings from the United Kingdom (U.K.) are depicted in the following graph that was published by the NY Times. Delta was still the dominant variant in the U.K. during the period for the data represented by this graph (Sept 6 through Oct 3, 2021), and booster shots had not been widely distributed yet.

• "When Can the U.S. Declare Victory Over Covid?", Spencer Bokat-Lindell, NY Times, 11/17/21

The graph shows the number of persons in the United Kingdom who were hospitalized between September 6 and October 3, 2021. For every 100,000 persons who were infected, the dark bars show the number of unvaccinated persons who were hospitalized; the light bars show the number of breakthroughs who were hospitalized. 

Our concern for older residents directs our attention to the last two pairs of bars on the righthand side of the graph. Assuming that hospitalizations in the U.S. follow patterns similar to those in the U.K. with regards to hospitalizations by age groups, we will use the U.K. data to make rough projections as to what might be expected from Omicron

• Oldest unvaccinated hospitalizations
  For every 100,000 persons who were infected, about 70 persons (dark bar) between ages 70 to 79 were hospitalized who were unvaccinated (or not fully vaccinated); about 99 persons (dark bar) 80 or older were hospitalized who were unvaccinated (or not fully vaccinated) 
  Subtotal = 70 + 99 = 169
  
  
• Oldest vaccinated hospitalizations
  For every 100,000 persons who were infected, about 22 persons (dark bar) between ages 70 to 79 were hospitalized who were fully vaccinated; about 49 persons (dark bar) 80 or older were hospitalized who were fully vaccinated  
  Subtotal = 22 + 49 = 71
  Total = 240

If Omicron proves to be at least twice as transmissible as Delta, then we should expect that at least twice as many people in each age group will be infected during a similar one month time frame, but the number of expected hospitalizations will depend on Omicron's lethality compared to Delta's.

• Lethality(Omicron) = Lethality(Delta)
  We should expect twice as many people in each age group to be hospitalized
  Oldest unvaccinated = 2 * 169 = 338
  Oldest vaccinated = 2 * 71 = 142
  Total = 480
  These numbers might overwhelm local hospitals
  
  
• Lethality(Omicron) less than Lethality(Delta), e.g., 75%
  We should expect lower Omicron hospitalizations, but larger than Delta's
  Oldest unvaccinated = 338 * 75% = 254
  Oldest vaccinated = 142 * 75% = 107
  Total = 361
  These lower numbers might also overwhelm local hospitals
  

Finally, returning to the original point of this article, we see that the number of infections in the entire population will be an unreliable predictor of hospitalizations under Omicron. But the number of infections among older residents might prove to be quite useful as a predictor of hospitalizations in a community

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Related notes on this blog:

• "Please remind me again: Why are we vaccinating? Why are we boosting?",  Last update: 12/10/21