COVID-19 Incidence and Death Rates Among Unvaccinated and Fully Vaccinated Adults with and Without Booster Doses During Periods of Delta and Omicron Variant Emergence

Abbreviations: FDA = Food and Drug Administration; IRR = incidence rate ratio; NC = not calculated for the single reported week of deaths in December 2021.
*Events per 100,000 population. Average weekly incidences and rate ratios are provided by age group, primary series vaccine type, and overall; overall and vaccine-specific rates were standardized by age, according to the enumerated 2000 U.S. Census age distribution. IRRs were calculated by dividing incidence among unvaccinated persons by incidence among fully vaccinated persons overall.
^†A COVID-19 case in a fully vaccinated person occurred when SARS-CoV-2 RNA or antigen was detected in a respiratory specimen collected ≥14 days after completing the primary series of a COVID-19 vaccine with FDA approval or emergency use authorization. A COVID-19 case in an unvaccinated person occurred when the person did not receive any FDA-authorized COVID-19 vaccine doses before the specimen collection date. Excluded were partially vaccinated persons who had received at least one FDA-authorized or approved vaccine dose but did not complete a primary series ≥14 days before collection of a specimen with SARS-CoV-2 RNA or antigen detected. This analysis represents the combined impact of BNT162b2 (Pfizer-BioNTech), mRNA-1273 (Moderna), and Ad.26.COV2.S (Janssen [Johnson & Johnson]) COVID-19 vaccines, which had different clinical efficacies against confirmed infection; fully vaccinated persons also include those persons who received additional primary doses and booster doses starting in mid-August. A COVID-19–associated death occurred in a person with a documented COVID-19 diagnosis who died, and whose report local health authorities reviewed (e.g., using vital records, public health investigation, or other data sources) to make that determination. Per national guidance, this should include persons whose death certificate lists COVID-19 disease or SARS-CoV-2 as an underlying cause of death or as a significant condition contributing to death. Rates of COVID-19 deaths by vaccination status are reported based on when the patient was tested for COVID-19, not the date they died.
^§Four analysis periods were designated based on the threshold week when the weighted proportions of lineages from whole-genome sequencing results submitted to or performed by CDC: pre-Delta (April 4–May 29, 2021: 0.1%–7% proportion range), Delta emergence (May 30–July 3, 2021: 14%–69%), Delta predominance (July 4–November 27, 2021: 81%–99%), and Omicron emergence (November 28–December 25, 2021: 1%–72%).
^¶Alabama, Arkansas, California, Colorado, District of Columbia, Florida, Georgia, Idaho, Indiana, Kansas, Louisiana, Massachusetts, Michigan, Minnesota, Nebraska, New Jersey, New Mexico, New York, New York City (New York), Rhode Island, Seattle/King County (Washington), Tennessee, Texas, Utah, and Wisconsin.
**95% CIs were calculated after detrending underlying linear changes in weekly incidence rates using piecewise linear regression. Each CI represents the remaining variation in observed weekly incidence rates and resulting incidence rate ratios. The number of observations informing each CI reflects the number of weeks per period: April–May (7), June (5), July–November (21), and December (4).
^††For deaths, a single week (November 28–December 4, 2021) of data was reported during the December 2021 period of Omicron emergence, but the proportion of Omicron variant during that first week was approximately 1%.

Abbreviations: FDA = Food and Drug Administration; IRR = incidence rate ratio; NC = not calculated for categories with counts <20; NR = not relevant for individual vaccine types because the comparison being made is to overall unvaccinated counts and age-adjusted rates.
*Events per 100,000 population.
^†Average weekly incidence rates and rate ratios are provided by age group, primary series vaccine type, and overall; overall and vaccine-specific rates were standardized by age, according to the enumerated 2000 U.S. Census age distribution. IRRs were calculated by dividing incidence among unvaccinated persons by incidence among fully vaccinated persons (overall and by receipt of booster doses).
^§A COVID-19 case in a fully vaccinated person occurred when SARS-CoV-2 RNA or antigen was detected in a respiratory specimen collected ≥14 days after completing the primary series of a COVID-19 vaccine with FDA approval or emergency use authorization. A COVID-19 case in an unvaccinated person occurred when the person did not receive any FDA-authorized COVID-19 vaccine doses before the specimen collection date. Excluded were partially vaccinated persons who had received at least one FDA-authorized or approved vaccine dose but did not complete a primary series ≥14 days before collection of a specimen with SARS-CoV-2 RNA or antigen detected. This analysis represents the combined impact of BNT162b2 (Pfizer-BioNTech), mRNA-1273 (Moderna), and Ad.26.COV2.S (Janssen [Johnson & Johnson]) COVID-19 vaccines, which had different clinical efficacies against confirmed infection; fully vaccinated persons also include those persons who received additional primary doses and booster doses starting in mid-August. A COVID-19–associated death occurred in a person with a documented COVID-19 diagnosis who died, and whose report local health authorities reviewed (e.g., using vital records, public health investigation, or other data sources) to make that determination. Per national guidance, this should include persons whose death certificate lists COVID-19 disease or SARS-CoV-2 as an underlying cause of death or as a significant condition contributing to death. Rates of COVID-19 deaths by vaccination status are reported based on when the patient was tested for COVID-19, not the date they died.
^¶A COVID-19 case in a fully vaccinated person with a booster dose occurred when a person had SARS-CoV-2 RNA or antigen detected on a respiratory specimen collected ≥14 days after receipt of at least one additional or booster dose of any COVID-19 vaccine on or after August 13, 2021. On August 13, 2021, CDC recommended an additional Pfizer-BioNTech or Moderna primary series dose for persons with moderately or severely immunocompromise. On September 24, 2021, CDC recommended a Pfizer-BioNTech booster dose for certain Pfizer-BioNTech primary series recipients, including all adults aged ≥65 years and persons aged ≥18 years in certain populations and high risk occupational and institutional settings. On October 21, 2021, CDC recommended a booster dose for adults aged ≥18 years who received the Janssen vaccine and for Pfizer-BioNTech or Moderna primary series recipients, including all adults aged ≥65 years and persons aged ≥18 years in certain populations and high risk occupational and institutional settings. On November 19, 2021, and November 29, 2021, CDC expanded recommendations for booster doses to include all adults aged ≥18 years.
**Reporting is by primary series vaccine type rather than additional or booster dose vaccine type. The booster dose vaccine type may be different than the primary series vaccine type. For primary mRNA vaccination series, the vaccine product of the second dose was used to determine primary series product type. If the Janssen vaccine was either the first dose or the second dose, the series type was called Janssen. The overall fully vaccinated group includes FDA-approved vaccinations of unknown vaccine type.
^††Analysis periods for this table were designated based on robust reporting of cases among persons with booster doses from October 2021 and the threshold week when the weighted proportions of lineages from whole-genome sequencing results submitted to or performed by CDC: October 3–November 27, 2021 (Delta predominance: 99%), and November 28–December 25, 2021 (Omicron emergence: 1%–72%).
^§§Alabama, Arkansas, California, Colorado, District of Columbia, Florida, Georgia, Idaho, Indiana, Kansas, Louisiana, Massachusetts, Michigan, Minnesota, Nebraska, New Jersey, New Mexico, New York, New York City (New York), Rhode Island, Seattle/King County (Washington), Tennessee, Texas, Utah, and Wisconsin.
^¶¶95% CIs were calculated after detrending underlying linear changes in weekly incidence rates using piecewise linear regression. Each CI represents the remaining variation in observed weekly incidence rates and resulting incidence rate ratios. The number of observations informing each CI reflects the number of weeks per period: October–November (7), and December (4).
***https://www.cdc.gov/nchs/data/statnt/statnt24.pdf

Authors and Disclosures

Amelia G. Johnson, DrPH^1,*, Avnika B. Amin, PhD^1,*, Akilah R. Ali, MPH¹, Brooke Hoots, PhD¹, Betsy L. Cadwell, PhD¹, Shivani Arora, MPH², Tigran Avoundjian, PhD³, Abiola O. Awofeso, DVM⁴, Jason Barnes, MBA⁵, Nagla S. Bayoumi, DrPH⁶, Katherine Busen, MPH⁷, Carolyn Chang, MPH⁸, Mike Cima, PhD⁹, Molly Crockett, MPH¹⁰, Alicia Cronquist, MPH¹¹, Sherri Davidson, PhD¹², Elizabeth Davis, MA¹³, Janelle Delgadillo⁵, Vajeera Dorabawila, PhD¹⁴, Cherie Drenzek, DVM¹⁵, Leah Eisenstein, MPH¹⁶, Hannah E. Fast, MPH¹⁷, Ashley Gent, MPH¹⁶, Julie Hand, MSPH¹⁸, Dina Hoefer, PhD¹⁴, Corinne Holtzman, MPH¹⁹, Amanda Jara, DVM¹⁵, Amanda Jones, MPH²⁰, Ishrat Kamal-Ahmed, PhD²¹, Sarah Kangas, MPH²², FNU Kanishka, MPH²¹, Ramandeep Kaur, PhD¹², Saadiah Khan, MPH⁶, Justice King, MSc¹, Samantha Kirkendall, MS²³, Anna Klioueva, MPH²⁴, Anna Kocharian, MS²², Frances Y. Kwon, MPH², Jacqueline Logan, MPH²⁵, B. Casey Lyons, MPH²⁶, Shelby Lyons, MPH¹⁸, Andrea May, MPH²⁷, Donald McCormick, MSHI⁹, Erica Mendoza, MAS²⁴, Lauren Milroy, MPH²⁸, Allison O'Donnell, MPH¹⁰, Melissa Pike, MPH¹¹, Sargis Pogosjans, MPH³, Amy Saupe, MPH¹⁹, Jessica Sell, MPH⁸, Elizabeth Smith, MPH¹⁵, Daniel M. Sosin, MD¹³, Emma Stanislawski, MPH¹³, Molly K. Steele, PhD¹, Meagan Stephenson, MPH¹, Allen Stout, MS⁷, Kyle Strand²¹, Buddhi P. Tilakaratne, PhD⁴, Kathryn Turner, PhD²³, Hailey Vest, MPH²⁸, Sydni Warner, MS²², Caleb Wiedeman, MPH²⁵, Allison Zaldivar, MPH²⁷, Benjamin J. Silk, PhD¹ and Heather M. Scobie, PhD<sup>1

1</sup>Epidemiology Task Force, COVID-19 Emergency Response Team, CDC; ²Rhode Island Department of Health; ³Public Health – Seattle & King County, Seattle, Washington; ⁴District of Columbia Department of Health; ⁵Utah Department of Health; ⁶New Jersey Department of Health; ⁷Michigan Department of Health and Human Services; ⁸New York City Department of Health and Mental Hygiene, New York; ⁹Arkansas Department of Health; ¹⁰Massachusetts Department of Public Health; ¹¹Colorado Department of Public Health and Environment; ¹²Alabama Department of Public Health; ¹³New Mexico Department of Health; ¹⁴New York State Department of Health; ¹⁵Georgia Department of Public Health; ¹⁶Florida Department of Health; ¹⁷Vaccine Task Force, COVID-19 Response Team, CDC; ¹⁸Louisiana Department of Health; ¹⁹Minnesota Department of Health; ²⁰Center for Surveillance, Epidemiology, and Laboratory Services, CDC; ²¹Nebraska Department of Health and Human Services; ²²Wisconsin Department of Health Services; ²³Idaho Department of Health and Welfare; ²⁴Texas Department of State Health Services; ²⁵Tennessee Department of Health; ²⁶Data Analytics and Visualization Task Force, CDD COVID-19 Emergency Response Team; ²⁷Kansas Department of Health and Environment; ²⁸Indiana Department of Health.

Corresponding author
Heather M. Scobie, vih8@cdc.gov.

All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Leah Eisenstein reports ownership of 100 shares of Pfizer stock. No other potential conflicts of interest were disclosed.

Sidebar

Summary

What is already known about this topic?

Although COVID-19 vaccine effectiveness decreased with emergence of the Delta variant and waning of vaccine-induced immunity, protection against hospitalization and death has remained high.

What is added by this report?

In 25 U.S. jurisdictions, decreases in case incidence rate ratios for unvaccinated versus fully vaccinated persons with and without booster vaccine doses were observed when the Omicron variant emerged in December 2021. Protection against infection and death during the Delta-predominant period and against infection during Omicron emergence were higher among booster vaccine dose recipients, especially among persons aged 50–64 and ≥65 years.

What are the implications for public health practice?

COVID-19 vaccination protected against SARS-CoV-2 infection, even as the Omicron variant became predominant. All eligible persons should stay up to date with COVID-19 vaccination.

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