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Centers for Disease Control and Prevention
National Center for Immunization and Respiratory Diseases
Centers for Disease Control and Prevention
National Center for Immunization and Respiratory Diseases
Centers for Disease Control and Prevention
National Center for Immunization and Respiratory Diseases
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 yearsOrganization 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 Primary3–8 weeks
Primary
***At least
8 weeksAges 6 months –
5 years
(Primary Series: Moderna )PrimaryPrimary
**4–8 weeksPediatric 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 bi valent 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 -b ased drive -through SARS-CoV -2 testing via pharmacies
Self- r eported vaccine history at time of registration for COVID -19 testing
Design : T est -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*** –F ebruary 5, 2023, BA.4/BA.5 predominant period, but 
includes XBBIncreasing 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, underlyin g 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 1stdoses started 7/4/2022; Pfizer 2nddose started 7/25/2022; Moderna 2nddose 
started 8/1/2022; Pfizer 3rddose 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
7Fleming -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 va ccines 
received and for the most recent dose, month and year of receipt; therefore, the number of months between a vaccine dose and tes ting is a 
whole number calculated as the difference between the month and year of testing and the month and year of the vaccine dose. F or 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 
testsSARS-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
1monovalent 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
V accine E ffectiveness (%)
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
8Fleming -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 va ccines 
received and for the most recent dose, month and year of receipt; therefore, the number of months between a vaccine dose and tes ting is a 
whole number calculated as the difference between the month and year of testing and the month and year of the vaccine dose. F or 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 
testsSARS- 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
V accine E ffectiveness (%)
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 hig h* ; 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 a
bility to estimate VE, including against more severe outcomes.Limitations
*https://covid.cdc.gov/covid-data-tracker/#pediatric-seroprevalence.9
Complete mo novalent 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 M oderna 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 -B ioNTech 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 -1 9 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 an
d 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: c omparing 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: c omparing 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 th
e additional protection provided by an updated bivalent booster among people 
who already received monovalent COVID -19 vaccinesInterpreting absolute and relative vaccine effectiveness 
12
Nationwide community- bas ed drive -through SARS-CoV -2 testing via pharmacies
Self-repo rted 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: E xcluded individuals <4 months from last monovalent dose and individuals with 
immunocompromising conditions
Periods for analysis:
•Tested: December 1, 2022 –F ebruary 13, 2023**
•Includes periods of both BA.5-rel ated sublineage and XBB/XBB.1.5 sublineage predominanceICATT: 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, underlyin g 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 SARS -
CoV- 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.htm13
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. 14Age group, years/mRNA Dosage PatternTotal
testsSARS-CoV -2 
positive tests, Adjusted VE
N (row %) (95% CI)
5-11 years (authorized for bivalent booster 
on October 12, 2022)
Received 2 -3monovalent 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. 15Age group, years/mRNA Dosage PatternTotal
testsSARS- 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 monovalen t 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 a djusted 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 SARS-
CoV-2
 17
mRNA Dosage PatternTotal 
testsSARS- 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 ≥2monovalent 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. 19mRNA Dosage Pattern Total testsSARS -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 : P rospective test-negative, case -control
Period :  September 8, 2022 –January 30, 2023
Population: Immunocompetent adults
h
ospitalized with COVID -like illness (CLI)
Participants have CLI and SARS-C oV-2 test:
–
–Cases: S ARS -CoV-2-positive by RT -PCR or 
antigen
Controls: S ARS -CoV-2-and influenza- negative 
by RT -PCR
VE adjustments: Ag e, 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*
CharacteristicCase -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 v accine effectiveness, if unvaccinated or vaccinated 
individuals are significantly different than the rest of the population, estimates may 
be biased.
For estimates of relative v accine effectiveness, residual protection from prior doses is 
an important consideration.
–
–Particularly important for severe disease, for which residual protection from prior doses may be higherCan be challenging to interpret waning of relative VE
Limited information on prior infection, although we know rates of prior infection in 
t
he U.S. population are high. 
VE against COVID -1 9 associated hospitalization may underestimate protection against 
severe COVID -19 disease.Limitations
26
Updates to VE of bivalent C OVID -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 C OVID -19 booster against ED/UC encounters and 
hospitalizations among adults ≥18 years
Bivalent boosters are helping provide additional protection against e
mergency 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 -Dutr a
Ruth Link- G elles
Morgan Najdowski
Sara Oliver
Amanda Payne
Lauren Roper
Laura Steinhardt
Evelyn Twentyman
Megan Wallace
Ryan WiegandPIs and study staff for VE platforms
Sarah Ball
Jennifer DeCuir
Monica Dickerson
Margaret Dunne
Eric Griggs
Matthew Levy
Patrick Mitchell
Palak PatelAcknowledgements
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 o f 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.