Centers for Disease Control and Prevention

National Center for Immunization and Respiratory Diseases

Photographs and images included in this presentation are licensed solely for CDC/NCIRD online and presentation use. No rights are implied or extended for use in printing or any use by other CDC CIOs or any external audiences.

COVID-19 vaccine effectiveness updates

24 February 2023

Amadea Britton, MD, SM

Medical Officer, Vaccine Effectiveness and Policy Team

Centers for Disease Control and Prevention
 Preliminary vaccine effectiveness (VE) of monovalent vaccines against 

symptomatic infection in children aged 6 months–4 years (Pfizer-BioNTech) 

and 6 months–5 years (Moderna)

 Update on VE of bivalent vaccines against symptomatic infection in children 

and adolescents aged 5-17 years and adults aged ≥18 years

 Update on VE of bivalent vaccines against severe disease in adults with a 

focus on adults aged ≥ 65 years

Organization of presentation

2
Preliminary Estimates of Effectiveness of mRNA Vaccines in 

Preventing Symptomatic SARS-CoV-2 Infection Among Children Aged 3–5 

Years — Increasing Community Access to Testing Program, United States, July 

2022–February 2023

Fleming-Dutra KE, Ciesla AA, Roper, LE et al. Preliminary Estimates of Effectiveness of Monovalent mRNA Vaccines in Preventing Symptomatic SARS-CoV-2 Infection 

Among Children Aged 3–5 Years — Increasing Community Access to Testing Program, United States, July 2022–February 2023. MMWR Morb Mortal Wkly Rep 

2023;72:177–182. DOI: http://dx.doi.org/10.15585/mmwr.mm7207a3

3
Ages 6 months–

4 years

(Primary Series: 

Pfizer-BioNTech)

Primary Primary

3–8 weeks

Primary

***

At least

8 weeks

Ages 6 months–

5 years

(Primary Series: 

Moderna)

Primary Primary

**

4–8 weeks

Pediatric COVID-19 Vaccine Primary Series Schedule*:

Ages 6 months–5 years (Moderna) and 6 months–4 years (Pfizer-BioNTech) 

*On June 18, 2022, ACIP issued interim recommendations for the use of the Moderna COVID-19 vaccine for children aged 6 months–5 years and for the Pfizer-BioNTech COVID-19 vaccine for children aged 6 

months–4 years. 

** As of December 9, 2022, children who received 2 doses of monovalent Moderna vaccine are recommended to receive a single bivalent booster dose at least 2 months after their last primary series dose.

***As of December 9, 2022, children who received 2 doses of monovalent Pfizer-BioNTech vaccine primary series are recommended to receive a bivalent dose as their third dose.

Earliest date for a child to

have a “complete series”=

August 1, 2022

Earliest date for a child 

to have a “complete 

series”=

September 19, 2022

4
Percent of people receiving COVID-19 vaccine by age and date administered 

– United States, December 14, 2020 – February 15, 2023

https://covid.cdc.gov/covid-data-tracker/#vaccination-demographics-trends 5
 Nationwide community-based drive-through SARS-CoV-2 testing via pharmacies

 Self-reported vaccine history at time of registration for COVID-19 testing

 Design: Test-negative, case-control analysis*

 Population: Immunocompetent children 3 – 4/5** years with ≥1 COVID-like symptom 

and nucleic acid amplification testing (NAAT)

 Period for analysis:

• Tested: July 4, 2022*** – February 5, 2023, BA.4/BA.5 predominant period, but 

includes XBB

Increasing Community Access to Testing (ICATT) Program: VE of monovalent

COVID-19 vaccines against symptomatic infection in children aged 3-5 years

*Models adjusted for: age, gender, race, ethnicity, social vulnerability index and HHS region of the testing location, underlying conditions (presence versus absence), pharmacy 

chain conducting the test, local incidence (cases per 100,000 by individual county and state in the 7 days before test date), and date of testing.

** ICATT testing is generally limited to children ages 3 and up.

***Analysis start date depended on vaccine/dose number being analyzed: Pfizer and Moderna 1st doses started 7/4/2022; Pfizer 2nd dose started 7/25/2022; Moderna 2nd dose 

started 8/1/2022; Pfizer 3rd dose started 9/19/2022. 6
ICATT: Preliminary estimates of VE for primary series monovalent Moderna vaccine 

(children aged 3–5 years) against symptomatic infection, July 4, 2022 – February 5, 2023

7

Fleming-Dutra, Ciesla, Roper, et al. MMWR February 16, 2023.

*Test registrants who report receiving COVID-19 vaccines are asked to report the total number of doses and manufacturer(s) of vaccines 

received and for the most recent dose, month and year of receipt; therefore, the number of months between a vaccine dose and testing is a 

whole number calculated as the difference between the month and year of testing and the month and year of the vaccine dose. For doses 

received in the same month or the month before SARS-CoV-2 testing, an additional question was asked to specify whether the dose was 

received ≥2 weeks before testing, and only doses received ≥2 weeks before testing were included. 17% and 21% of children who received 1 

and 2 doses of Moderna, respectively, reported a prior infection >90 days before the current test.

Vaccination status (months since last dose) Total 

tests

SARS-CoV-2

positive, N (%)

Adjusted

VE (95% CI)

Moderna, 1 dose (partial series; ages 3-5 years)

July 4, 2022 – February 5, 2023

Unvaccinated 34,982 9,523 (27) Ref

1 monovalent dose (2 weeks–1 month)* 509 107 (21) 40 (26 to 52)

Moderna, 2 doses (complete series; ages 3-5 years)

August 1, 2022 – February 5, 2023

Unvaccinated 25,049 5,690 (23) Ref

2 monovalent doses (2 weeks–2 months)* 816 81 (10) 60 (49 to 68)

2 monovalent doses (3–4 months)* 495 58 (12) 36 (15 to 52)

-20 0 20 40 60 80 100

Vaccine Effectiveness (%)
ICATT: Preliminary estimates of VE for primary series monovalent Pfizer-BioNTech vaccine 

(children aged 3–4 years) against symptomatic infection, July 4, 2022 – February 5, 2023

8

Fleming-Dutra, Ciesla, Roper, et al. MMWR February 16, 2023.

*Test registrants who report receiving COVID-19 vaccines are asked to report the total number of doses and manufacturer(s) of vaccines 

received and for the most recent dose, month and year of receipt; therefore, the number of months between a vaccine dose and testing is a 

whole number calculated as the difference between the month and year of testing and the month and year of the vaccine dose. For doses 

received in the same month or the month before SARS-CoV-2 testing, an additional question was asked to specify whether the dose was 

received ≥2 weeks before testing, and only doses received ≥2 weeks before testing were included. 18%, 19% and 21% of children who 

received 1, 2, and 3 doses of Pfizer, respectively, reported a prior infection >90 days before the current test.

**There was insufficient power to stratify Pfizer-BioNTech 3-dose VE estimates by time since vaccination.

Vaccination status (months since last dose) Total 

tests

SARS-CoV-2

positive, N (%)

Adjusted

VE (95% CI)

Pfizer, 1 dose (partial series; ages 3–4 years)

July 4, 2022–February 5, 2023

Unvaccinated 22,323 6,212 (28) Ref

1 monovalent dose (2 weeks–1 month)* 443 114 (26) 19 (-1 to 35)

Pfizer, 2 doses (partial series; ages 3–4 years)

July 25, 2022–February 5, 2023

Unvaccinated 17,434 4,298 (25) Ref

2 monovalent doses (2 weeks–3 months)* 933 137 (15) 40 (28 to 50)

Pfizer, 3 doses (complete series; ages 3–4 years)**

September 19, 2022–February 5, 2023

Unvaccinated 7,548 1,273 (17) Ref

3 monovalent doses (2 weeks–4 months)* 395 53 (13) 31 (7 to 49)

-20 0 20 40 60 80 100

Vaccine Effectiveness (%)
Vaccine coverage is low in children ≤5 years. VE estimates may 

be less stable when vaccine coverage is low. 

 Prevalence of prior infection in children is high*; consequently, 

vaccine effectiveness in this analysis reflects the current 

situation among young children in the United States.

 Low vaccination coverage in this age group may impact future 

ability to estimate VE, including against more severe outcomes.

Limitations

*https://covid.cdc.gov/covid-data-tracker/#pediatric-seroprevalence. 9
 Complete monovalent primary vaccination series helped provide protection for 

children aged 3–5 years against symptomatic SARS-CoV-2 infection for at least the 

first 4 months after vaccination.

 Waning of monovalent Moderna primary series might occur by 3–4 months after the 

second dose based on point estimates (although confidence intervals overlapped). 

This is similar to patterns observed in older children and adults in the first months 

after vaccination. 

– Waning of monovalent Pfizer-BioNTech VE against symptomatic infection could not be assessed but is also 

likely based on analyses in older children and adults. 

 Children should stay up to date with COVID-19 vaccines, including completing the 

primary series; those who are eligible should receive a bivalent vaccine dose.

 CDC will continue to monitor VE in this age group, including against severe disease 

and for bivalent doses.

Conclusions

10
Updated estimates of VE against 

symptomatic infection among children and 

adolescents aged 5–17 and adults aged ≥18 

years

11
 Absolute VE: comparing the frequency of health outcomes in vaccinated and 

unvaccinated people 

–

–

E.g., comparing outcomes in people vaccinated with an updated bivalent booster versus no 

vaccine at all

 Relative VE: comparing the frequency of health outcomes in people who received 

one type of vaccine to people who received a different vaccine or by comparing 

people who received more vaccine doses to those who received fewer doses 

E.g., comparing outcomes in people vaccinated with an updated bivalent booster versus 

monovalent vaccine only

 In the analyses presented today, relative vaccine effectiveness can be interpreted as 

the additional protection provided by an updated bivalent booster among people 

who already received monovalent COVID-19 vaccines

Interpreting absolute and relative vaccine effectiveness 

12
 Nationwide community-based drive-through SARS-CoV-2 testing via pharmacies

 Self-reported vaccine history at time of registration for COVID-19 testing

 Design: Test-negative, case-control analysis*

 Population: Children and adolescents aged 5–17 years and adults aged ≥18 years with ≥1 COVID-like 

symptom and nucleic acid amplification testing (NAAT)

 Exclusion criteria: Excluded individuals <4 months from last monovalent dose and individuals with 

immunocompromising conditions

 Periods for analysis:

• Tested: December 1, 2022 – February 13, 2023**

• Includes periods of both BA.5-related sublineage and XBB/XBB.1.5 sublineage predominance

ICATT: Relative VE of bivalent booster against symptomatic infection in 

children and adolescents aged 5–17 years and adults aged ≥18 years

*Models adjusted for: age, gender, race, ethnicity, social vulnerability index and HHS region of the testing location, underlying conditions (presence versus absence), local incidence (cases per 100,000 by individual county and 

state in the 7 days before test date), and date of testing

**Analysis is an update of data published in Link-Gelles R, Ciesla AA, Roper LE, et al. Early estimates of bivalent mRNA booster dose vaccine effectiveness in preventing symptomatic SARS-CoV-2 infection attributable to SARSCoV-2 Omicron BA.5-related and XBB/XBB.1.5-related sublineages among immunocompetent adults—Increasing Community Access to Testing Program, United States, December 2022–January 2023. MMWR Morb Mortal Wkly

Rep 2023;72. https://www.cdc.gov/mmwr/volumes/72/wr/mm7205e2.htm 13
ICATT: Relative VE of bivalent booster against symptomatic infection in children and 

adolescents aged 5–17 years, December 1, 2022 – February 13, 2023*

*Unpublished CDC data. 14

Age group, years/mRNA Dosage Pattern

Total

tests

SARS-CoV-2 

positive tests, Adjusted VE

N (row %) (95% CI)

5-11 years (authorized for bivalent booster 

on October 12, 2022)

Received 2-3 monovalent doses only (Ref) 4,855 1,433 (30) Ref

2 weeks-1 month since bivalent booster 600 73 (12) 65 (55 to 73)

2-3 months since bivalent booster 881 139 (16) 54 (43 to 62)

4-5 months since bivalent booster 58 10 (17) ----

12-17 years (authorized for bivalent booster 

on September 1, 2022)

Received 2-3 monovalent doses only (Ref) 8,243 3,194 (39) Ref

2 weeks-1 month since bivalent booster 443 73 (16) 68 (58 to 75)

2-3 months since bivalent booster 1,122 230 (20) 56 (49 to 62)

4-5 months since bivalent booster 283 68 (24) 53 (37 to 64)

0 20 40 60 80 100

Vaccine Effectiveness %
ICATT: Relative VE of bivalent booster against symptomatic infection in adults aged 

≥18 years, December 1, 2022 – February 13, 2023*

*Unpublished CDC data. 15

Age group, years/mRNA Dosage Pattern Total

tests

SARS-CoV-2 

positive tests, Adjusted VE

N (row %) (95% CI)

18-49 years

Received 2-3 monovalent doses only (Ref) 182,741 82,043 (45) Ref

2 weeks-1 month since bivalent booster 10,758 3,127 (29) 51 (49 to 53)

2-3 months since bivalent booster 32,577 10,206 (31) 45 (43 to 46)

4-5 months since bivalent booster 9,197 2,882 (31) 41 (38 to 44)

50-64 years

Received 2-4 monovalent doses only (Ref) 60,822 31,878 (52) Ref

2 weeks-1 month since bivalent booster 6,223 2,331 (37) 46 (43 to 49)

2-3 months since bivalent booster 18,399 7,898 (43) 32 (29 to 34)

4-5 months since bivalent booster 4,837 2,030 (42) 28 (23 to 32)

≥65 years

Received 2-4 monovalent doses only (Ref) 28,307 14,246 (50) Ref

2 weeks-1 month since bivalent booster 4,579 1,788 (39) 38 (34 to 42)

2-3 months since bivalent booster 19,071 8,080 (42) 27 (25 to 30)

4-5 months since bivalent booster 5,796 2,431 (42) 21 (16 to 26)

0 20 40 60 80 100

Vaccine Effectiveness %
Updated estimates of VE against 

emergency department/urgent care encounters 

and hospitalizations among adults aged ≥18 

years, VISION Network
VISION Multi-State Network of Electronic Health Records

 Variant periods designated for 

analysis based on time when novel 

sublineage became predominant at 

study site

 VE adjusted for age, sex, race, 

ethnicity, geographic region, 

calendar time, and local rates of 

SARS-CoV-2 circulation

 Vaccination documented by 

electronic health records and state 

and city registries

 Cases: COVID-like illness (CLI) with 

positive PCR for SARS-CoV-2 within 14 

days before or 72 hours after the 

admission or encounter

 Controls: CLI with negative PCR for SARSCoV-2 17
mRNA Dosage Pattern Total 

tests

SARS-CoV-2-

test-positive,

N (%)

Median interval

since last dose,

days (IQR)

Adjusted VE

(95% CI)

Emergency department/urgent care encounters

Aged 18-64 years

Unvaccinated (Ref) 56,560 6,632 (12) — Ref

Monovalent doses only, last dose ≥2 months earlier 79,203 8,848 (11) 370 (300-508) 2 (-2 to 5)

Aged ≥65 years

Unvaccinated (Ref) 11,277 2,026 (18) — Ref

Monovalent doses only, last doses ≥2 months earlier 37,505 5,588 (15) 335 (196-424) 12 (6 to 17)

Hospitalizations

Aged 18-64 years

Unvaccinated (Ref) 6,213 475 (8) — Ref

Monovalent doses only, last doses ≥2 months earlier 7,250 501 (7) 360 (281-502) 19 (7 to 30)

Aged ≥65 years

Unvaccinated (Ref) 4,795 819 (17) — Ref

Monovalent doses only, last doses ≥2 months earlier 14,462 1924 (13) 337 (205-439) 28 (22 to 34)

VISION: Absolute VE of ≥2 monovalent doses against ED/UC encounters and 

hospitalizations among adults aged ≥18 years– September 2022 – January 

2023*

*Unpublished CDC data.

-20 0 20 40 60 80 100

Vaccine Effectiveness (%)

18
VISION: Relative VE of bivalent booster against ED/UC encounters and 

hospitalizations among adults aged ≥18 years –September 2022 – January 

2023*

*Unpublished CDC data. 19

mRNA Dosage Pattern Total tests

SARS-CoV-2-

test-positive,

N (%)

Median 

interval

since last 

dose,

days (IQR)

Adjusted VE

(95% CI)

Emergency department/urgent care encounters

Monovalent doses only, last dose ≥2 months earlier 112,857 13,429 (12) 359 (279-496) Ref

Bivalent booster, 7-59 days earlier 12,546 948 (8) 33 (20-46) 50 (46 to 53)

Bivalent booster, 60-119 days earlier 5,952 617 (10) 76 (67-87) 36 (30 to 41)

Hospitalizations

Monovalent doses only, last dose ≥2 months earlier 28,227 3,187 (11) 348 (243-484) Ref

Bivalent booster, 7-59 days earlier 2,809 202 (7) 32 (19-45) 52 (44 to 58)

Bivalent booster, 60-119 days earlier 1,281 155 (12) 74 (67-85) 31 (18 to 42)

0 20 40 60 80 100

Vaccine Effectiveness (%)
Preliminary estimates of VE against 

hospitalizations among adults aged ≥65 years, 

IVY Network
IVY Network — 24 hospitals, 19 U.S. States

 Design: Prospective test-negative, case-control

 Period: September 8, 2022–January 30, 2023

 Population: Immunocompetent adults

hospitalized with COVID-like illness (CLI)

 Participants have CLI and SARS-CoV-2 test:

–

–

Cases: SARS-CoV-2-positive by RT-PCR or 

antigen

Controls: SARS-CoV-2- and influenza-negative 

by RT-PCR

 VE adjustments: Age, sex, race/ethnicity, 

admission date (biweekly), and HHS region

21
Vaccinated 

cases, 

N/total cases 

(%)

Vaccinated 

controls, 

N/total 

controls 

(%)

Median 

interval

since last 

dose,

days (IQR)

Adjusted 

VE,

% (95% CI)

Absolute monovalent VE against hospitalization 

Unvaccinated (Ref) -- Ref

≥2 Monovalent doses, last dose ≥2 months earlier 550/707 (78) 645/810 (80) 352 (224-432) 17 (-7 to 36)

Relative bivalent VE against hospitalization 

≥2 Monovalent doses, last dose ≥2 months earlier (Ref) 352 (224-432) Ref

Bivalent booster dose, ≥7 days earlier 108/658 (16) 255/900 (28) 56 (30–84) 52 (37–64)

Absolute bivalent VE against hospitalization 

Unvaccinated (Ref) -- Ref

Bivalent booster dose, ≥ 7 days earlier 108/265 (41) 255/420 (61) 56 (30–84) 55 (36–69)

IVY: Absolute VE of ≥2 monovalent doses and relative VE of bivalent booster against 

COVID-19 hospitalizations among adults aged ≥65 years — IVY Network, September 8, 

2022–January 30, 2023*

*Unpublished CDC data.

-20 0 20 40 60 80 100

Vaccine Effectiveness (%)

22
Vaccinated 

cases, 

N/total cases 

(%)

Vaccinated 

controls, 

N/total 

controls 

(%)

Median 

interval

since last 

dose,

days (IQR)

Adjusted 

VE,

% (95% CI)

Absolute monovalent VE against hospitalization 

Unvaccinated (Ref) -- Ref

≥2 Monovalent doses, last dose ≥2 months earlier 550/707 (78) 645/810 (80) 352 (224-432) 17 (-7 to 36)

Relative bivalent VE against hospitalization 

≥2 Monovalent doses, last dose ≥2 months earlier (Ref) 352 (224-432) Ref

Bivalent booster dose, ≥7 days earlier 108/658 (16) 255/900 (28) 56 (30–84) 52 (37–64)

Absolute bivalent VE against hospitalization 

Unvaccinated (Ref) -- Ref

Bivalent booster dose, ≥7 days earlier 108/265 (41) 255/420 (61) 56 (30–84) 55 (36–69)

IVY: Absolute VE of ≥2 monovalent doses and relative VE of bivalent booster against 

COVID-19 hospitalizations among adults aged ≥65 years — IVY Network, September 8, 

2022–January 30, 2023*

*Unpublished CDC data.

-20 0 20 40 60 80 100

Vaccine Effectiveness (%)

23
IVY: Severity of COVID-19 hospitalizations in bivalent booster VE analysis among 

adults aged ≥65 years — IVY Network, September 8, 2022–January 30, 2023*

Characteristic

Case-patients, N (%)

N = 719**

Hypoxemia 427 (59)

High flow nasal cannula (HFNC) 78 (11)

Non-invasive positive pressure ventilation (NIPV) 51 (7)

Invasive mechanical ventilation (IMV) 47 (7)

HFNC, NIPPV, or IMV 138 (19)

ICU admission 116 (16)

In-hospital death on or before Day 28 38 (5)

*Unpublished CDC data.

**Data missing for 12% (96/815) of cases due to reporting lag.

• Of all hospitalized cases, 

59% had documented 

hypoxemia

• Approximately 16% of 

hospitalized cases required 

an ICU admission

• Some hospitalizations 

included in the analysis may 

not represent severe 

COVID-19 disease 

24
Conclusions
 For estimates of absolute vaccine effectiveness, if unvaccinated or vaccinated 

individuals are significantly different than the rest of the population, estimates may 

be biased.

 For estimates of relative vaccine effectiveness, residual protection from prior doses is 

an important consideration.

–

–

Particularly important for severe disease, for which residual protection from prior doses may be higher

Can be challenging to interpret waning of relative VE

 Limited information on prior infection, although we know rates of prior infection in 

the U.S. population are high. 

 VE against COVID-19 associated hospitalization may underestimate protection against 

severe COVID-19 disease.

Limitations

26
 Updates to VE of bivalent COVID-19 booster against symptomatic infection 

among children and adolescents aged 5-17 years and adults aged ≥18 years 

–

–

Bivalent booster provided added protection, though early evidence of 

waning of relative effectiveness

 Updates to VE of bivalent COVID-19 booster against ED/UC encounters and 

hospitalizations among adults ≥18 years

Bivalent boosters are helping provide additional protection against 

emergency department/urgent care encounters and hospitalization

– For most people who received monovalent doses and are eligible for a 

bivalent booster, more than a year has elapsed since their last monovalent 

dose. Because of waning, they may have limited remaining protection.

Conclusions

27
CDC COVID-19 Vaccine Effectiveness and 

Policy Team

 Allison Ciesla

 Monica Godfrey

 Katherine Fleming-Dutra

 Ruth Link-Gelles

 Morgan Najdowski

 Sara Oliver

 Amanda Payne

 Lauren Roper

 Laura Steinhardt

 Evelyn Twentyman

 Megan Wallace

 Ryan Wiegand

PIs and study staff for VE platforms

 Sarah Ball

 Jennifer DeCuir

 Monica Dickerson

 Margaret Dunne

 Eric Griggs

 Matthew Levy

 Patrick Mitchell

 Palak Patel

Acknowledgements

28

 Sarah Reese

 Heather Scobie

 Zach Smith

 Diya Surie

 Zack Weber

 Mark Tenforde
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.

Photographs and images included in this presentation are licensed solely for CDC/NCIRD online and presentation use. No rights are implied or extended for use in printing or 

any use by other CDC CIOs or any external audiences.