Comparing Cases, Deaths, and Hospitalizations Indicates Omicron Less Deadly

Since the beginning of the pandemic, clinicians, public health officials, policymakers, and the public have relied on data about cases, deaths, testing and hospitalizations to understand the ever changing realities of COVID-19. As the disease appears to be shifting into an endemic phase with less severity, these data, particularly cases, are becoming less reliable given how many infections were detected with at-home tests never recorded in public reports.¹ When dealing with volatile numbers, it is better to rely on trends and comparisons to better understand the data. For instance, knowing that a state had 50,000 new cases is less informative than understanding that this represents a 20,000 decrease from the previous week, indicating that spread is diminishing.

The importance of tracking trends is obvious when looking at the complete U.S. datasets for cases, deaths, and hospitalizations below. Steep increases in any of the individual metrics correlate with the beginning of a wave driven by a new variant (Alpha, Delta, and Omicron in order). When the trend flips and the counts decrease, leaders consider us to be coming out of the wave, and can make policy changes accordingly. Based on the most recent data, it would appear that the Omicron wave has dwindled.

For a better understanding of how society is actually handling these trend changes, we can turn to comparisons in the form of ratios. The ratio of deaths to cases gives some insight into the mortality rate – how many reported cases become deaths. The percentage in no way signifies the true mortality of COVID-19 due to many asymptomatic, unreported cases, but the trend can inform us as to how deadly the disease is currently. When comparing cases and deaths, we apply a three-week lag to fatality data because it takes time for cases to become deaths and then get reported.² The lag is visible in the first image where the peaks for deaths during variant waves do not line up with the peaks for cases and hospitalizations.

As shown above, the deaths-to-cases ratio has been pretty consistent throughout the pandemic once our reporting systems were fully established in summer 2020. Deaths have represented about 2% of reported COVID-19 cases. However, that finally changed with Omicron. During the Omicron wave, mortality decreased significantly, with deaths now representing less than 0.5% of reported cases. Additional testing of asymptomatic or mild cases could also explain this change, but testing infrastructure use has decreased over the past few months. The data trends clearly demonstrate that Omicron is a much less deadly variant, which is critical for downgrading COVID-19 to an endemic disease. The reduced severity of Omicron could also be attributed in part to increased vaccination coverage and recovery immunity

The functionality of hospitals is also of critical importance, as when they are flooded with COVID-19 patients — even if fewer patients are dying of COVID-19 — those trying to get to the hospital for other reasons could be turned away for lack of space. Since hospitalization and case reporting occur at similar times, there is no lag incorporated into a ratio of how many infections result in hospital admissions. However, some cases do not require hospitalization immediately, but worsen over time, resulting in some hospitalizations having a lag to the case data. The size of this effect is impossible for us to quantify due to the lack of publicly available line-level data that tracks individual COVID-19 trajectories, so we are assuming that the effect is small enough to warrant the use of no lag time.

This ratio has previously been used to understand where testing is most prevalent.³ When the ratio increases, hospitals are performing more testing relative to other venues like laboratories, indicating there are more patients present with COVID-19. During the Delta wave in summer 2021, this ratio increased rapidly as hospitals were overwhelmed with COVID-19 patients. Many people needing emergency care were turned away during this time as hospitals were over capacity.⁴ Comparatively, during Omicron, this ratio has decreased. Hospital testing capacity has not significantly diminished, so it could indicate that the number of COVID-19 patients is decreasing and hospitals can handle the load. Hospitals have still suffered during the Omicron wave due to areas with higher case rates and staff contracting COVID-19,⁵ but this data indicates that the U.S. healthcare system as a whole should have been able to handle the Omicron wave despite individual hospitals being overwhelmed. In addition, if COVID-19 remains generally mild, the system can tolerate it. Issues regarding private insurance networks and who can access which hospitals complicate the concept of overall national hospital capacity, and a further reduction in COVID-19 hospitalizations would help alleviate the pressure on all systems. Taken together these data tell us that Omicron was less deadly than previous variants and that if COVID-19 does become an endemic, seasonal disease with similar severity, the country is better prepared. We are not there yet and public health experts will continue to watch these data and perform surveillance for new variants before declaring the pandemic over. While it would be an atypical viral evolution trajectory, a new variant as severe as Delta or the original strain would be a significant blow to the hope kindled by the diminishing Omicron wave. We need to remain watchful and continue recording and reporting COVID-19 data, but we are on an encouraging trajectory.

References

1. M. Gandhi, L. Bienen, As Omicron Hits, COVID-19 Case Counts Don't Mean What They Used To, 16 December 2021. https://time.com/6129225/omicron-covid-19-case-counts/. (Accessed 01 March 2022).
2. C.C. Testa, N. Krieger, J.T. Chen, W.P. Hanage, Visualizing the lagged connection between COVID-19 cases and deaths in the United States: An animation using per capita state-level data (January 22, 2020 – July 8, 2020) Harvard Center for Population and Development Studies Working Paper Series (10 July 2020).
3. D. Zweig, Our Most Reliable Pandemic Number Is Losing Meaning, 13 September 2021. https://www.theatlantic.com/health/archive/2021/09/covid-hospitalization-numbers-can-be-misleading/620062/. (Accessed 28 February 2022).
4. B. Balch, “Worst surge we’ve seen”: Some hospitals in delta hot spots close to breaking point, 24 August 2021. https://www.aamc.org/news-insights/worst-surge-we-ve-seen-some-hospitals-delta-hot-spots-close-breaking-point. (Accessed 01 March 2022).
5. J. Kaleem, E. Baumgaertner, Sick staff. Endless COVID patients. Doctors ‘just scraping by’ as Omicron sweeps hospitals, 13 January 2022. https://www.latimes.com/world-nation/story/2022-01-13/omicron-hospitals-covid-staff. (Accessed 01 March 2022).