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Overlapping Delta and Omicron Outbreaks During the COVID-19 Pandemic: Dynamic Panel Data Estimates.
Lundberg, Alexander L; Lorenzo-Redondo, Ramon; Hultquist, Judd F; Hawkins, Claudia A; Ozer, Egon A; Welch, Sarah B; Prasad, P V Vara; Achenbach, Chad J; White, Janine I; Oehmke, James F; Murphy, Robert L; Havey, Robert J; Post, Lori A.
  • Lundberg AL; Buehler Center for Health Policy and Economics, Robert J Havey, MD Institute for Global Health, Northwestern University, Chicago, IL, United States.
  • Lorenzo-Redondo R; Department of Emergency Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States.
  • Hultquist JF; Department of Medicine, Division of Infectious Diseases, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States.
  • Hawkins CA; Center for Pathogen Genomics and Microbial Evolution, Robert J Havey, MD Institute for Global Health, Northwestern University, Chicago, IL, United States.
  • Ozer EA; Department of Medicine, Division of Infectious Diseases, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States.
  • Welch SB; Center for Pathogen Genomics and Microbial Evolution, Robert J Havey, MD Institute for Global Health, Northwestern University, Chicago, IL, United States.
  • Prasad PVV; Department of Medicine, Division of Infectious Diseases, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States.
  • Achenbach CJ; Center for Global Communicable and Emerging Infectious Diseases, Robert J Havey, MD Institute for Global Health, Northwestern University, Chicago, IL, United States.
  • White JI; Department of Medicine, Division of Infectious Diseases, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States.
  • Oehmke JF; Center for Pathogen Genomics and Microbial Evolution, Robert J Havey, MD Institute for Global Health, Northwestern University, Chicago, IL, United States.
  • Murphy RL; Buehler Center for Health Policy and Economics, Robert J Havey, MD Institute for Global Health, Northwestern University, Chicago, IL, United States.
  • Havey RJ; Department of Emergency Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States.
  • Post LA; Sustainable Intensification Innovation Lab, Kansas State University, Manhattan, KS, United States.
JMIR Public Health Surveill ; 8(6): e37377, 2022 06 03.
Article in English | MEDLINE | ID: covidwho-2198054
ABSTRACT

BACKGROUND:

The Omicron variant of SARS-CoV-2 is more transmissible than prior variants of concern (VOCs). It has caused the largest outbreaks in the pandemic, with increases in mortality and hospitalizations. Early data on the spread of Omicron were captured in countries with relatively low case counts, so it was unclear how the arrival of Omicron would impact the trajectory of the pandemic in countries already experiencing high levels of community transmission of Delta.

OBJECTIVE:

The objective of this study is to quantify and explain the impact of Omicron on pandemic trajectories and how they differ between countries that were or were not in a Delta outbreak at the time Omicron occurred.

METHODS:

We used SARS-CoV-2 surveillance and genetic sequence data to classify countries into 2 groups those that were in a Delta outbreak (defined by at least 10 novel daily transmissions per 100,000 population) when Omicron was first sequenced in the country and those that were not. We used trend analysis, survival curves, and dynamic panel regression models to compare outbreaks in the 2 groups over the period from November 1, 2021, to February 11, 2022. We summarized the outbreaks in terms of their peak rate of SARS-CoV-2 infections and the duration of time the outbreaks took to reach the peak rate.

RESULTS:

Countries that were already in an outbreak with predominantly Delta lineages when Omicron arrived took longer to reach their peak rate and saw greater than a twofold increase (2.04) in the average apex of the Omicron outbreak compared to countries that were not yet in an outbreak.

CONCLUSIONS:

These results suggest that high community transmission of Delta at the time of the first detection of Omicron was not protective, but rather preluded larger outbreaks in those countries. Outbreak status may reflect a generally susceptible population, due to overlapping factors, including climate, policy, and individual behavior. In the absence of strong mitigation measures, arrival of a new, more transmissible variant in these countries is therefore more likely to lead to larger outbreaks. Alternately, countries with enhanced surveillance programs and incentives may be more likely to both exist in an outbreak status and detect more cases during an outbreak, resulting in a spurious relationship. Either way, these data argue against herd immunity mitigating future outbreaks with variants that have undergone significant antigenic shifts.
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Full text: Available Collection: International databases Database: MEDLINE Main subject: SARS-CoV-2 / COVID-19 Type of study: Experimental Studies / Observational study / Prognostic study / Randomized controlled trials Topics: Variants Limits: Humans Language: English Journal: JMIR Public Health Surveill Year: 2022 Document Type: Article Affiliation country: 37377

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Full text: Available Collection: International databases Database: MEDLINE Main subject: SARS-CoV-2 / COVID-19 Type of study: Experimental Studies / Observational study / Prognostic study / Randomized controlled trials Topics: Variants Limits: Humans Language: English Journal: JMIR Public Health Surveill Year: 2022 Document Type: Article Affiliation country: 37377