cdc.gov/coronavirus

COVID-19 Vaccine Effectiveness

in the United States

Ruth Link-Gelles, PhD, MPH

Co-Lead, Vaccine Effectiveness Team

CDC COVID-19 Response

LCDR, US Public Health Service

ACIP Meeting

September 22, 2021
Monitoring vaccine effectiveness (VE) evidence 

by risk group, outcome, and product over time

X Outcome X Product

Desired, but often limited by sample size

By time since vaccination and/or pre-/post-Delta

Risk group
Increasing Community Access to Testing (ICATT) Partnership 

Waning of immunity by Delta predominance in 

the general population
 Nationwide community-based COVID-19 testing via pharmacies and partners

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

those who did not report vaccination status (18%)

 Design: Test-negative, case-control assessment 

 Period: Pre-Delta: March 13–May 29 (N=255,519); Delta: July 18–August 31 (N=519,699)

 Population: Persons aged 20–64 years of age with COVID-like illness (CLI) and 

laboratory-based nucleic acid amplification testing (NAAT)

 Adjusted for: – Calendar day, race, ethnicity, gender, site’s HHS region and state, site census tract’s social vulnerability index (SVI)

– Not adjusted for underlying conditions or prior infection

Increasing Community Access to Testing (ICATT) Partnership: 

VE analysis for symptomatic infection, March 13–August 31, 2021
Pfizer-BioNTech VE against 

symptomatic infection by age 

group and time since vaccination 

in pre-Delta vs Delta periods 

Pre-Delta (March 13–May 29) with 

95% CIs in dotted lines

Delta (July 18–August 31) with 

95% CIs in dotted lines

• Significant waning of VE in both time 

periods

• VE is lower during Delta period at all 

time points

• Curves look similar across age groups
Moderna VE against 

symptomatic infection by age 

group and time since vaccination 

in pre-Delta and Delta periods 

Pre-Delta (March 13–May 29) with 

95% CIs in dotted lines

Delta (July 18–August 31) with 

95% CIs in dotted lines

• Moderna VE is higher than PfizerBioNTech

• VE wanes during Delta

• Curves look similar across age groups
Johnson & Johnson (J&J, 

Janssen) VE against symptomatic 

infection by age group and time 

since vaccination in pre-Delta 

and Delta periods 

Pre-Delta (March 13–May 29) with 

95% CIs in dotted lines

Delta (July 18–August 31) with 

95% CIs in dotted lines

• VE increases with time in both periods

• No clear Delta effect on VE

• Curves look similar across age groups

Number of days from dose date Number of days from dose date

Number of days from dose date Number of days from dose date
 Self-reported vaccination data, no clinical assessment – By limiting to persons with known vaccination status, a substantial proportion of records were lost, possibly 

introducing bias 

 No information on co-morbidities, prior infection, risk behaviors

 Analysis based on tests, no unique identifiers to track individuals in data

 No genetic sequencing results

– Pre-Delta: March 13–May 29

– Delta: July 18–August 31

ICATT limitations for VE against symptomatic infection
Vaccine effectiveness in individuals ≥65 years of 

age, including residents of long-term care 

facilities
*Vaccine effectiveness calculated using previously described methods: Moline et al. Effectiveness of COVID-19 Vaccines in Preventing Hospitalization Among Adults Aged ≥65 Years — COVID-NET, 13 States, February–April 2021. MMWR, 

August 13, 2021

‡California, Colorado, Connecticut, Georgia, Maryland, Michigan, Minnesota, New Mexico, New York, Ohio, Oregon, Tennessee, and Utah are included in these analyses

COVID-19-Associated Hospitalization Surveillance 

Network (COVID-NET) 

 Population-based surveillance for laboratoryconfirmed COVID-19-associated hospitalizations

 Defined catchment area: >250 acute care hospitals 

in 99 counties in 14 states, representing 10% of 

U.S. population

 Case definition: Resident of the surveillance area 

and positive SARS-CoV-2 test within 14 days prior 

to or during hospitalization

 VE estimates: variation of screening method

– Immunization information systems (ISS)

– Representative sample of hospitalized cases 

(>37,000 to date) 

– Underlying population in catchment area by 

week 

Represents ~10% of U.S. population (32 million people)

 VE estimates adjusted for time, but cannot adjust 

for other important potential confounders (e.g., 

comorbidities, prior infection)
0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

April May June July August

Vaccine Effectiveness

18-29 years 30-49 years 50-64 years 65-74 years 75 years and up

11

COVID-NET vaccine effectiveness against hospitalization, 

by month and age group, mRNA vaccines

Among fully vaccinated patients, defined as receipt of both doses of Moderna or Pfizer-BioNTech vaccine, with second dose received ≥14 days before 

hospitalization

Source: Unpublished COVID-NET data, 2021

No significant 

differences in VE by 

age group or 

calendar month of 

hospitalization
COVID-19-associated hospitalizations among vaccinated adults ≥18 years 

with COVID-19 as primary reason for admission — COVID-NET, January 

1–July 31, 2021

* All characteristics were significantly different on univariate analysis 12

Category Unvaccinated

weighted %

N=5,513

Fully vaccinated

weighted %

N=465

Age group (median, IQR) 59 (47–71) 72 (62–80)

18–49 years 28 11

50–64 years 33 16

≥65 years 40 72

LTCF residence 5 13

DNR/DNI/CMO 6 16

Underlying medical conditions

Cardiovascular disease 34 50

Neurologic disease 17 28

Renal disease 16 29

Immunosuppressive condition 12 29

Rheumatologic or autoimmune 3 7

Blood disorder 3 4

≥3 Underlying medical conditions 55 66

 Fully vaccinated cases 

more likely to be:

– Older 

– Long-term care 

facility resident

– DNR/DNI code

 More underlying 

medical conditions
 NY State linked lab, immunization, and hospitalization data to estimate VE from 

May 3–August 29, 2021 – 147,937 new diagnoses among fully vaccinated and unvaccinated persons

– 16,261 new hospitalizations among fully vaccinated and unvaccinated persons

 Breakdown by vaccine:

– Pfizer-BioNTech: 52%

– Moderna: 39%

– Johnson & Johnson/Janssen: 9%

 Delta proportion: <2% (May 2–8) to >99% (August 22–28) (CDC NS3, HHS Reg. 2)

VE against infection and hospitalization: Data from NY State, 

May–July 2021

Update of published study: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e1.htm
VE against infection: Data from NY State, May–August 2021

Update of published study: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e1.htm

Age-adjusted VE against new COVID-19 

infections declined from 92% (May 3–9) 

to 73% (July 12–18), when Delta 

reached 85%. Then, decline ceased, 

with plateau around 77%.
VE against hospitalization: Data from NY State, May-August 2021

Update of published study: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e1.htm

Age-adjusted VE against new 

COVID-19 hospitalizations 

remained stable at 90%–95%.
VISION Multi-State Network of Electronic Health Records for 

VE against hospitalization

Estimates are from over 74,000 

hospitalizations across 187 hospitals

 VE for adults aged ≥18 years

 Cases: COVID-like illness (CLI) with positive PCR 

for SARS-CoV-2

 Controls: CLI with negative PCR for SARS-CoV-2

 VE adjusted for propensity to be vaccinated, 

calendar time, site-region, local virus circulation, 

and age

– Waning VE models are matched on calendar week 

and site and restricted to six of seven VISION sites

 Vaccination documented by electronic health 

records and state and city registries 

 Median age of cases: 65 years (IQR 48-77)
82% 85% 82% 82% 93% 84% 86%

73%

0%

20%

40%

60%

80%

100%

January to

May

June to

August

January to

May

June to

August

January to

May

June to

August

January to

May

June to

August

18-29 years 30-49 years 50-64 years 65+ years

Vaccine effectiveness (%)

VISION Network: VE against hospitalization by time 

period and age group, Pfizer-BioNTech and Moderna

17

91% 82% 85% 99% 93% 91% 91%

86%

0%

20%

40%

60%

80%

100%

Jan to May Jun to Aug Jan to May Jun to Aug Jan to May Jun to Aug Jan to May Jun to Aug

18-29 years 30-49 years 50-64 years 65+ years

Vaccine effectiveness (%)

PfizerBioNTech

Moderna

* p<0.05

*
90%

92% 90% 93% 89% 86%

78%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

14 days to <2

mo

14 days to <2

mo

2 to <4 mo 14 days to <2

mo

2 to <4 mo 4 to <5 mo ≥5 mo

January to

March 2021

April to May 2021 June to August 2021

Vaccine effectiveness (%)

VISION Network: Preliminary VE against hospitalization by time since 

vaccination in each calendar period, adults ≥18 years, mRNA products

*

* p<0.05 for trend
VISION Network: Preliminary VE against hospitalization by time since 

vaccination in each calendar period, adults ≥18 years, mRNA products

*

Among people recently 

vaccinated (<2 months), 

VE against hospitalization 

has remained high. VE has 

declined among those 

who have been vaccinated 

for longer periods of time.

90%

92% 90% 93% 89% 86%

78%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

14 days to <2

mo

14 days to <2

mo

2 to <4 mo 14 days to <2

mo

2 to <4 mo 4 to <5 mo ≥5 mo

January to

March 2021

April to May 2021 June to August 2021

Vaccine effectiveness (%)

* p<0.05 for trend
90%

92% 90% 93% 89% 86%

78%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

14 days to <2

mo

14 days to <2

mo

2 to <4 mo 14 days to <2

mo

2 to <4 mo 4 to <5 mo ≥5 mo

January to

March 2021

April to May 2021 June to August 2021

Vaccine effectiveness (%)

VISION Network: Preliminary VE against hospitalization by time since 

vaccination in each calendar period, adults ≥18 years, mRNA products

*

Among people recently 

vaccinated (<2 months), 

VE against hospitalization 

has remained high. VE has 

declined among those 

who have been vaccinated 

for longer periods of time.

* p<0.05 for trend
68%

60%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta

Vaccine Effectiveness

VISION Network: VE against hospitalization by time 

period and age group, Johnson & Johnson/Janssen

https://www.nejm.org/doi/full/10.1056/NEJMoa2110362 

https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e2.htm 21

≥50 years ≥18 years
 Data from National Healthcare Safety Network (NHSN)

 Nursing homes report weekly aggregate number of residents and cases by 

vaccination status (product and number of doses received) to NHSN

 VE estimated for three periods:

1) Pre-Delta (March 1–May 9) 

2) Intermediate (May 10–June 20)

3) Delta (June 21–August 1)

VE of mRNA vaccines against infection among nursing home 

residents before and during widespread Delta circulation

Nanduri et al. MMWR: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e2.htm

Pre-Delta 

(Mar 1–May 9)

Intermediate 

(May 10–Jun 20)

Delta

(Jun 20–Aug 1)

No. of weekly reports 17,407 33,160 85,593

No. of facilities 3,862 11,581 14,917
NHSN: VE against infection during Delta period differed 

significantly from pre-Delta period

Adapted from: Nanduri S. Effectiveness of Pfizer-BioNTech and Moderna Vaccines in Preventing SARS-CoV-2 Infection Among Nursing Home Residents Before and During 

Widespread Circulation of the SARS-CoV-2 B.1.617.2 (Delta) Variant — National Healthcare Safety Network, March 1–August 1, 2021. MMWR Morbidity and Mortality Weekly 

Report. 2021 2021;70. Slide courtesy of Ian Plumb.

74.7

67.5

53.1

74.2

66.5

52.4

74.7

70.4

50.6

0

10

20

30

40

50

60

70

80

90

100

Vaccine effectiveness against infection

Pre-Delta Intermediate Delta Pre-Delta Intermediate Delta Pre-Delta Intermediate Delta

Overall Pfizer-BioNTech Moderna
NHSN (mRNA)

COVID-NET (mRNA)

VISION (Pfizer)

VISION (Moderna)

NYS (all products) 

NYS (all products)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta

Vaccine effectiveness (%)

Magnitude of VE against infection or hospitalization by 

Delta predominance for adults ≥65 years of age, by study

NHSN: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e3.htm

COVID-NET: CDC unpublished VISION: CDC unpublished 24

 Decline of 15–25 percentage points for 

point estimates against infection

 Hospitalization data mixed

 Larger decline for Pfizer-BioNTech 

(VISION)

 Smaller declines for combined 

mRNA products and Moderna 

alone
Vaccine effectiveness for adults with underlying 

medical conditions
https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e3.htm

Vaccine effectiveness of mRNA vaccines against COVID-19-

associated hospitalization: SUPERNOVA Network

 Design: Test-negative, case-control assessment 

 Period: February 1–August 6, 2021

 Population: U.S. Veterans (aged ≥18 years) hospitalized at 

5 Veterans Administration Medical Centers

 Participants

– Cases: COVID-like illness (CLI) and SARS-CoV-2-positive 

test results by RT-PCR

– Controls: CLI and SARS-CoV-2-negative test results by 

RT-PCR

 Demographics:

– Median age: 68 years – 49% Black, non-Hispanic – 44% with Charlson Comorbidity Index score ≥3

• 70% hypertension; 47% obesity; 43% diabetes

SUrveillance Platform for Enteric and 

Respiratory iNfectious Organisms at the VA
SUPERNOVA: VE against COVID-19-associated 

hospitalization, by mRNA vaccine

https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e3.htm

92%

77%

97%

87%

95%

80%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

18-64 years ≥65 18-64 years ≥65 18-64 years ≥65

Vaccine Effectiveness (%)

Pfizer-BioNTech Moderna Combined mRNA
SUPERNOVA: mRNA VE against COVID-19-associated hospitalization, by 

Delta variant predominance and time since vaccination

https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e3.htm 28

84%

89% 86% 87%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

February 1-June 30 July 1-August 6 <90 days since full vaccination ≥90 days 

Vaccine Effectiveness (%)

Pre-Delta vs. Delta Time since full vaccination
Effectiveness of mRNA vaccines for preventing COVID-19 

hospitalization, IVY Network

Tenforde et al. MMWR https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e2.htm

 Population: Adults (≥18 years) hospitalized at 21

medical centers in 18 states

 Case status:

– Cases with COVID-19-like illness and

SARS-CoV-2 antigen / RT-PCR (+)

– Controls: SARS-CoV-2 RT-PCR (-)

 SARS-CoV-2 testing within 10 days of admission, and admission within 14 days of 

illness onset

 Analytic period: Admitted March 11–August 15, 2021
IVY Network: COVID-19 vaccine effectiveness against hospitalization by vaccine product 

and time since vaccination, adults ≥18 years without immunocompromising conditions

91%

77%

93% 92%

68%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

14-120 days

after full

vaccination

>120 days

after full

vaccination

14-120 days

after full

vaccination

>120 days

after full

vaccination

>28 days after full

vaccination

Vaccine Effectiveness

Pfizer-BioNTech Moderna Janssen

* Adjusted for admission date (biweekly), HHS region, age, sex, race/ethnicity. Not enough recipients of Janssen to assess by time since vaccination.
IVY Network: COVID-19 vaccine effectiveness against hospitalization by age group and 

time since vaccination, adults without immunocompromising conditions, mRNA vaccines

31

93%

88%

91%

81%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

14-120 days

after full vaccination

>120 days

after full vaccination

14-120 days

after full vaccination

>120 days

after full vaccination

Vaccine Effectiveness

18–64 years ≥65 years
IVY Network: COVID-19 vaccine effectiveness against hospitalization by age group and 

Delta predominance, adults without immunocompromising conditions, mRNA vaccines

https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e2.htm 32

92% 91% 91%

87%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta Pre-Delta Delta

Vaccine Effectiveness

18–64 years ≥65 years
IVY Network: COVID-19 mRNA vaccine effectiveness against 

hospitalization among adults by risk group and Delta predominance, excluding 

patients with immunocompromising conditions

CDC unpublished; estimates are controlled for age. 33

97% 98%

89%

85%

90%

85%

92% 90%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta Pre-Delta Delta Pre-Delta Delta Pre-Delta Delta

No underlying condtions ≥ 1 underlying conditions Hypertension Obesity

Vaccine Effectiveness
SUPERNOVA 

(mRNA)

IVY ≥1 

underlying 

condtion (all 

products)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta

Vaccine effectiveness (%)

Magnitude of VE against infection or hospitalization by Delta 

predominance for adults with underlying medical conditions, by study

SUPERNOVA: https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e3.htm

IVY: CDC unpublished data 34

 No VE estimates available for 

infection

 VE estimates for hospitalization, 

remain high during Delta
Vaccine effectiveness for workers employed in 

occupations with high risk of exposure to

SARS-CoV-2
HEROES-RECOVER Cohorts

https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e4.htm

 Prospective cohort of over 4,000 healthcare personnel, 

first responders, and other frontline workers in 8 U.S. 

locations

 VE of full vaccination in preventing symptomatic and 

asymptomatic SARS-CoV-2 infection 

– Routine weekly swabbing plus illness specimens

– Multi-method vaccination documentation; 95% mRNA 

vaccines

– Hazard person-time model adjusted for study site, 

occupation, and local virus circulation and weighted for 

propensity to be vaccinated (socio-demographics, health, 

frequency of close contact and mask use)

– 62% female; 72% aged 18–49 years; 31% with ≥1 underlying 

medical condition
Adjusted VE against infection

% (95% CI)

Full cohort to date

Overall VE 80 (69-80)

14-119 days post dose 2 85 (68-93)

120-149 days post dose 2 81 (34-95)

≥150 days post dose 2 73 (49-86)

Pre-Delta variant predominance, overall VE 91 (81-96)

Delta variant predominance, overall VE 66 (26-84)

HEROES/RECOVER: VE against SARS-CoV-2 infection by Delta 

variant predominance and time since full vaccination

https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e4.htm

 VE against infection (80% symptomatic) declined from 91% pre-Delta to 66% during Delta

 Did not have enough power to look at time since vaccination pre-Delta and during Delta

 Do not see significant difference between mRNA products

0 20 40 60 80 100

Vaccine Effectiveness (%)
Summary and conclusions
HEROESRECOVER 

(mRNA)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta

Vaccine effectiveness (%)

SUPERNOVA 

(mRNA)

IVY ≥1 

underlying 

condtion (all 

products)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta

Vaccine effectiveness (%)

Magnitude of VE against infection or hospitalization by 

Delta predominance and study, by risk group

NHSN: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e3.htm

COVID-NET: CDC unpublished VISION: https://www.nejm.org/doi/10.1056/NEJMoa2110362/ https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e2.htm

IVY: CDC unpublished data SUPERNOVA: https://www.cdc.gov/mmwr/volumes/70/wr/mm7037e3.htm

NYS: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e1.htm HEROES-RECOVER: https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e4.htm 39

Underlying medical conditions Frontline workers

NHSN (mRNA)

COVID-NET (mRNA)

VISION (Pfizer)

VISION (Moderna)

NYS (all products) 

NYS (all products)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Pre-Delta Delta

Vaccine effectiveness (%)

≥ 65 years of age
 Individuals ≥65 years of age

– Significant declines in VE against infection for mRNA products in during Delta-variant predominant period

– Declines for hospitalization (with Pfizer-BioNTech greater than Moderna) in Delta-variant predominant period

– Evidence of waning in Delta-variant predominant period

 Individuals with underlying conditions

– No data on VE against infection; likely similar to overall population

– Similar patterns for VE for hospitalization as in general adult population

 Occupations with high risk of exposure to SARS-CoV-2 – No data on VE against hospitalization; likely similar to overall population

– Similar patterns for VE for infection as in general adult population

Summary & conclusions
Acknowledgements

 New York State Health Department

– Eli Rosenberg and co-authors

 Site PIs and teams for IVY, VISION, Signature, NHSN, 

HEROES/RECOVER, SUPERNOVA, COVID-NET

 CDC

– Sara Oliver

– Stephanie Schrag

– Katherine Fleming-Dutra

– Jennifer Verani

– John Jernigan

– Nong Shang

– Gordana Derado

– Stephanie Bialek

– Meredith McMorrow

– Epi and Vaccine Task Forces

 CDC

– Heather Scobie

– Mark Tenforde

– Srinivas Nanduri

– Tamara Pilishvili

– Diya Surie

– Mila Prill

– Kristina Bajema

– Mark Thompson

– Jill Ferdinands

– Ian Plumb

– Fiona Havers

– Heidi Moline

– Jessica Smith

– Manish Patel
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.