cdc.gov/coronavirus

Update on SARS-CoV-2 

Variants and the 

Epidemiology of COVID-19

CDR Heather Scobie, PhD, MPH

Coronavirus and Other Respiratory Viruses Division (Proposed)

Centers for Disease Control and Prevention

September 1, 2022
SARS-CoV-2 Variants
SARS-CoV-2 Omicron (B.1.1.529) variant

https://www.cdc.gov/coronavirus/2019-ncov/variants/omicron-variant.html

https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/scientific-brief-omicron-variant.html

Key mutations (yellow) in the 

Omicron spike protein (top view)

Source: New York Times

▪ Five main sub-lineages: BA.1 through BA.5

▪ Increased transmissibility and immune 

evasion, but decreased disease severity

▪ 30+ mutations in spike gene (S-gene)

– 15 in receptor binding domain

▪ Lower vaccine effectiveness

– Reduced neutralization by sera from vaccinated or 

convalescent individuals

▪ Reduction in efficacy of some monoclonal 

antibody treatments

3
PI=Prediction Interval, VOC=Variants of Concern, VBM=Variants Being Monitored. https://covid.cdc.gov/covid-data-tracker/#variant-proportions Accessed August 26, 2022

Trends in Weighted Variant Proportion Estimates & Nowcast

United States, May 22–August 27, 2022

Collection date, week ending

4
Estimated Number of Reported COVID-19 Cases by Variant 

Variant Proportions Scaled by Positive Nucleic Acid Amplification Test (NAAT) Counts

CDC COVID-19 Lab Coordinating Unit Strain Surveillance and Emerging Variant Group. Data sources: https://covid.cdc.gov/covid-data-tracker/#variant-proportions

and https://covid.cdc.gov/covid-data-tracker/#trends_newtestresultsreported_7daytestingpositive_00

6M

0

4M

2M

Positive tests / Proportion of viral lineages
Nowcast Estimates of Variant Proportions by HHS Region

United States, August 21–27, 2022

HHS=Health and Human Services 

https://covid.cdc.gov/covid-data-tracker/#variant-proportions Accessed August 26, 2022 6

B.4

BA.4.6

Omicron 

Sub-lineage

BA.2.12.1

BA.5
COVID-19 Trends
CDC COVID Data Tracker. https://covid.cdc.gov/covid-data-tracker/#trends_dailycases Accessed August 31, 2022

Daily Trends in Reported COVID-19 Cases, United States

Alpha Delta

Omicron

As of August 30, 2022:

94,268,241 reported cases

8
Daily Trends in Reported COVID-19 Cases and NAAT Percent 

Positivity (7-day Moving Average), United States

CDC COVID Data Tracker. https://covid.cdc.gov/covid-data-tracker/#trends_newtestresultsreported_7daytestingpositive_00 Accessed August 31, 2022 9

In May, trends in reported COVID19 cases and NAAT positivity (%) 

become uncoupled, related to 

decreases in provider testing and 

increases in at-home testing
Weekly Trends in COVID-19-Associated Hospitalization Rates

by Age Group — COVID-NET, March 2020 – August 20, 2022

Grey shaded area denotes the most recent 2 weeks where reporting is <95% complete.

Source: COVID-NET; https://gis.cdc.gov/grasp/COVIDNet/COVID19_3.html Accessed August 26, 2022 10

Age Group

Alpha

Delta

Omicron

Since April, 

hospitalization

rates in older age 

increased relative 

to other age groups 
21.5

10.5

4.4

2.2

10.7

7.0

4.0

2.4

6.2

4.7

3.1

2.3

0 2 4 6 8 10 12 14 16 18 20 22

85+ y

75-84 y

65-74 y

50-64 y

Hospitalization Rate Ratio

Age Group

Delta (Jun 20-Dec 18, 2021)

Omicron BA.1 (Dec 19, 2021-Mar 19, 2022)

Omicron BA.2 (Mar 20-May 31, 2022)

Hospitalization Rate Ratios by Age Group 

COVID-NET, June 2021 – May 31, 2022

Havers et al. MMWR 2022; 71(34);1085–1091. https://www.cdc.gov/mmwr/volumes/71/wr/mm7134a3.htm?s_cid=mm7134a3_w

Adults aged 18-49 years are the 

reference group for all periods

11
Characteristics of hospitalized adults ≥18 years 

COVID-NET, June 20, 2021 – May 31, 2022

* COVID-19–related illness as a likely reason for admission is indicated by COVID-19 diagnosis or symptoms consistent with COVID-19 as the chief complaint or reason for 

admission in the history of present illness. Non–COVID-19 reasons for admission included planned inpatient surgery or procedures, psychiatric admission needing acute 

medical care, trauma, other, and unknown. Havers et al. MMWR 2022; 71(34);1085–1091. https://www.cdc.gov/mmwr/volumes/71/wr/mm7134a3.htm?s_cid=mm7134a3_w

Characteristic

% of Total Hospitalizations

Delta

Jun 20, 2021–

Dec 18, 2021

(n=5,234)

Omicron BA.1

Dec 19, 2021–

Mar 19, 2022

(n=1,804)

Omicron BA.2

Mar 20, 2021–

May 31, 2022

(n=1,228)

Age Median (years) 59.9 63.8 70.5

Likely COVID-19–related* 95.5 87.8 85.4

Risk Factors

Any underlying medical condition 89.3 91.7 95.1

Immunosuppressive condition 11.0 16.0 19.2

Long-term care facility 5.7 9.0 14.2

Outcomes

Length of stay (days, median) 4.8 3.9 3.3

ICU admission 24.3 17.9 13.2

Mechanical ventilation 13.5 7.6 5.7

In-hospital death 12.4 7.5 5.1

Trends during 

BA.1 & BA.2

▪ Median age 

increased

▪ Underlying 

conditions 

more 

prevalent

▪ Clinical 

outcomes less 

severe

12
0

10

20

30

40

50

60

70

80

COVID-19-associated hospitalization 

rate per 1000,000 population

Calendar week ending date

American Indian/Alaska Native Asian/Pacific Islander Black Hispanic/Latino White

Age-Adjusted Rates of COVID-19-Associated Hospitalizations 

Among Persons of All Ages by Race/Ethnicity 

COVID-NET, March 7, 2020 – August 13, 2022 (3-Week Moving Average) 

Grey shaded area denotes the most recent 2 weeks where reporting is <95% complete.

COVID-19-Associated Hospitalization Surveillance Network (COVID-NET): https://covid.cdc.gov/covid-data-tracker/#covidnet-hospitalization-network. Accessed August 23, 2022

Recent 

hospitalization 

rates highest 

among American 

Indian/Alaskan 

Native and 

Black persons

13
Daily Trends in Number of COVID-19 Deaths, United States

Provisional Death Certificate Data, National Vital Statistics System 

14 https://www.cdc.gov/nchs/nvss/vsrr/covid_weekly/index.htm Accessed August 31, 2022

Alpha

Delta

Omicron As of August 27, 2022:

1,042,112 deaths
Weekly Trends in COVID-19 Mortality Rates by Age Group, 

United States, March 1, 2020 – August 20, 2022

Provisional Death Certificate Data, National Vital Statistics System

Source: https://data.cdc.gov/NCHS/Provisional-Weekly-Deaths-by-Region-Race-Age/tpcp-uiv5

Source: National Center for Health Statistics, National Vital Statistics System. Data accessed on August 25, 2022. Date provided for "Week of Death" references week-end date.

The gray box over the most recent two weeks indicates total death data for these weeks are less than 60% complete overall and should be interpreted with caution.
Weekly Trends in Age-Adjusted COVID-19 Mortality Rates by 

Race/Ethnicity, United States, March 1, 2020 – August 20, 2022

Provisional Death Certificate Data, National Vital Statistics System

Source: National Center for Health Statistics, National Vital Statistics System. Data accessed on August 25, 2022. Date provided for "Week of Death" references week-end date.

The gray box over the most recent two weeks indicates total death data for these weeks are less than 60% complete overall and should be interpreted with caution.

https://data.cdc.gov/NCHS/Provisional-Weekly-Deaths-by-Region-Race-Age/tpcp-uiv5 (National Vital Statistics System provisional death certificate data) 16

0

2

4

6

8

10

12

14

16

18

Mar-20 Jun-20 Sep-20 Dec-20 Mar-21 Jun-21 Sep-21 Dec-21 Mar-22 Jun-22

Age Adjusted Deaths per 100,000

Week of Death

American Indian/Alaska Native Asian/Pacific Islander Black Hispanic/Latino White
Weekly Trends in Age-Adjusted COVID-19 Mortality Rates by 

Race/Ethnicity, United States, March 1, 2020 – August 20, 2022

Provisional Death Certificate Data, National Vital Statistics System

Source: National Center for Health Statistics, National Vital Statistics System. Data accessed on August 25, 2022. Date provided for "Week of Death" references week-end date.

The gray box over the most recent two weeks indicates total death data for these weeks are less than 60% complete overall and should be interpreted with caution.

https://data.cdc.gov/NCHS/Provisional-Weekly-Deaths-by-Region-Race-Age/tpcp-uiv5 (National Vital Statistics System provisional death certificate data) 17

0

2

4

6

8

10

12

14

16

18

Mar-20 Jun-20 Sep-20 Dec-20 Mar-21 Jun-21 Sep-21 Dec-21 Mar-22 Jun-22

Age Adjusted Deaths per 100,000

Week of Death

American Indian/Alaska Native Asian/Pacific Islander Black Hispanic/Latino White

Recent mortality rates 

show less evidence of 

disparities
Trends in COVID-19 by Vaccination Status
As of August 24, 2022

COVID-19 Vaccinations in the United States

*This includes people who received booster doses and people who received additional primary doses.

https://covid.cdc.gov/covid-data-tracker/#vaccinations_vacc-total-admin-rate-total Accessed August 24, 2022

223.9M

People vaccinated 

with a primary series

108.5M

People received a 

first booster dose*

72% Population 

≥5 Years of Age

49% Population 

≥5 Years of Age

23.1M

People received a 

second booster dose*

34% Population 

≥50 Years of Age

Differences in vaccination 

coverage by:

• Age, with lower primary series 

coverage in children

• Race/ethnicity, with lower booster 

coverage in most minority groups

• Disability status
Age-Adjusted Rates of COVID-19 Cases by Vaccination Status 

Among Ages ≥5 years April 4, 2021 – July 23, 2022 (31 U.S. Jurisdictions)

CDC COVID Data Tracker. https://covid.cdc.gov/covid-data-tracker/#rates-by-vaccine-status Accessed August 24, 2022 20

In July 2022, unvaccinated people ages ≥5 years had 2.4X higher risk of testing positive for 

COVID-19, compared to those with at least a primary series

Alpha

Delta

Omicron
Age-Adjusted Rates of COVID-19-Associated Hospitalization by 

Vaccination Status and Receipt of Booster Dose in Adults Ages ≥18 Years 

COVID-NET, January 2021–June 2022

CDC COVID Data Tracker. https://covid.cdc.gov/covid-data-tracker/#covidnet-hospitalizations-vaccination Accessed August 3, 2022

Alpha

Delta

Omicron

In June 2022, 

unvaccinated adults 

ages ≥18 years had 

4.6X higher 

COVID-19-associated 

hospitalization rates 

compared to those 

vaccinated with at least 

one booster dose
Age-Adjusted Rates of COVID-19-Associated Deaths by Vaccination Status 

and Receipt of Booster Dose* Among Ages ≥5 years

September 19, 2021 – July 2, 2022 (29 U.S. Jurisdictions)

*This includes people who received booster doses and people who received additional doses. Vertical lines denote changes in booster dose recommendations.

CDC COVID Data Tracker. https://covid.cdc.gov/covid-data-tracker/#rates-by-vaccine-status Accessed August 24, 2022 22

In June 2022, 

unvaccinated people 

ages ≥5 years had 

8X higher 

COVID-19-associated 

death rates compared 

to those with at least 

one booster dose

This was a decrease 

from ~20X during

January-March 2022

Delta

Omicron
Death Rates by Vaccination Status and Receipt of 1st and 2nd Booster 

Doses Among People Ages ≥50 Years April 3–July 2, 2022 (25 U.S. Jurisdictions)

*Includes either a booster or additional dose. 

https://covid.cdc.gov/covid-data-tracker/#rates-by-vaccinbooine-status. Accessed August 24, 2022 

In June 2022, people ages 

50 years and older with 

≥2 booster doses had 

14 times lower risk of dying 

from COVID-19, compared 

to unvaccinated people and 

3 times lower risk of dying 

from COVID-19 than people

with one booster dose
▪ Unvaccinated people at higher risk of severe illness compared with vaccinated people

▪ Most (75%) vaccinated people with severe COVID-19 illness have multiple risk factors:

– Older age (most ≥65 years, but with risk increasing with age)

– Underlying medical conditions (with risk increasing with number of underlying 

conditions)

› Immunosuppression

› Diabetes mellitus

› Chronic kidney disease

› Chronic lung disease

› Chronic cardiovascular disease

› Chronic neurologic disease

▪ Antiviral drugs can help reduce risk of severe illness in people at higher risk, regardless 

of vaccination status

Risk of Severe COVID-19 Illness

Yek et al. MMWR 2022;71:19–25. https://www.cdc.gov/mmwr/volumes/71/wr/mm7101a4.htm; Taylor et al. MMWR 2022;71:466-473:

http://dx.doi.org/10.15585/mmwr.mm7112e2 and unpublished COVID-NET data, as described here; Malden et al. MMWR 2022; 71(25);830-833: 

https://www.cdc.gov/mmwr/volumes/71/wr/mm7125e2.htm ; Gold et al. MMWR 2022; 71(25);825-829: 

https://www.cdc.gov/mmwr/volumes/71/wr/mm7125e1.htm ; Najjar-Debbiny et al. CID 2022;, ciac443, https://doi.org/10.1093/cid/ciac443

Dryden-Peterson et al. medRxiv 2022.06.14.22276393; https://doi.org/10.1101/2022.06.14.22276393
▪ CDC continues to monitor emerging variants, like the sub-lineages of Omicron, 

including prevalence and impact on disease incidence, severity, and vaccine 

effectiveness over time

▪ Racial and ethnic minority groups have been disproportionately affected by 

COVID-associated hospitalization and mortality; these inequities have decreased 

over time but have not been eliminated

▪ Trend of increasing severe illness, including hospitalization and death, in people 

of older age and with underlying health conditions

▪ Currently approved vaccines offer protection against severe illness and death 

from COVID-19 — important to stay up to date with vaccination, including all 

boosters in eligible populations

▪ Therapeutics and multiple prevention measures should be used to protect 

people at higher risk of severe COVID-19 illness, regardless of vaccination status

Summary

25
▪ Amelia Johnson

▪ Lauren Linde

▪ Akilah Ali

▪ Justice King

▪ Meagan Stephenson

▪ Steve Evener

▪ Betsy Gunnels

▪ Benjamin Silk

▪ Chris Taylor

▪ Fiona Havers

▪ Ruth Link-Gelles

▪ Sara Oliver

▪ Evelyn Twentyman

▪ Katherine Fleming-Dutra

▪ Aron Hall

▪ Rebecca Kondor

▪ Phillip Shirk

▪ Clint Paden

▪ Natalie Thornburg

▪ Summer Galloway

▪ Dave Wentworth

▪ Taraesa Toney

▪ Andrea Yunyou

▪ State and local health departments: AL, AR, 

AZ, CA, CO, CT, DC, FL, GA, ID, IN, IO, KS, LA, 

MA, MD, MI, MN, NC, NE, NJ, NM, NY, NY 

City, OH, Philadelphia, RI, Seattle/King 

County, SD, TN, TX, UT, WA, WI, WV

Acknowledgements
For more information, contact CDC

1-800-CDC-INFO (232-4636)

TTY: 1-888-232-6348 www.cdc.gov

The findings and conclusions in this report are those of the authors and do not necessarily 

represent the official position of the Centers for Disease Control and Prevention.