Influenza
Conditions
Keywords
Flu vaccine, Influenza vaccine, Immune response, Influenza strain
Brief summary
The goal of this study is to understand the impact on the human immune system's response to the four strain flu vaccine in individuals who have imprinted on specific influenza strains. It will also consider the effects of repeated prior annual influenza vaccination on the immune system.
Detailed description
Seasonal influenza outbreaks continue to cause substantial disease burden, with an estimated 3-5 million cases of severe illness, and 250,000 to 500,000 deaths worldwide each year. In the United States, the Centers for Disease Control and Prevention (CDC) reports that influenza has resulted in 9.2-35.6 million illnesses with 12,000-56,000 deaths annually since 2010. There is an urgent need to better understand the immunologic responses to current licensed vaccines in order to develop a more effective vaccine that does not rely on annual updates, provides broad protection, and is durable; i.e., a universal influenza vaccine. The immune response to the influenza vaccine is affected by many parameters, including prior imprinting to a specific influenza strain based on birth cohort, as well as prior influenza vaccination. The FDA-approved, quadrivalent seasonal influenza vaccine that will be administered contains four distinct strains, two influenza A viruses (IAVs) and two influenza B viruses (IBVs). The approved seasonal influenza vaccine will be given for each season of influenza: 2018-2019, 2019-2020, and 2020-2021. This study is a prospective pilot study conducted over the course of three years (with three specific influenza seasons studied). For each year (2018-2019, 2019-2020, and 2020-2021), two cohorts of 10 participants each, who are in good health and meet all eligibility criteria, will be recruited. The influenza A virus subtype H3N2 cohort (N=30 total, 10 per year) will consist of participants born between 1968-1977, and the influenza A virus subtype H1N1 cohort (N=30 total, 10 per year) will consist of participants born between 1948-1957. Each participant will make a total of six visits to the Hope Clinic. Day 1 will include the informed consent process, and screening to ensure the subject meets all inclusion criteria and meets no exclusion criteria. For the consenting and eligible subject, the visit will also include pre-vaccination phlebotomy for baseline immunogenicity laboratory assays. After baseline sample collection, the participants will receive the FDA-approved seasonal influenza vaccine. Subsequent study visits up to 180 days post-vaccination will include collection for immunogenicity assays. This study is not powered to test a formal null hypothesis. Rather, it is a hypothesis-generating investigation that will hopefully lead to larger trials based on the findings. The study will be conducted over the course of three years to increase the total sample population size and to validate the findings over different influenza seasons.
Interventions
BIOLOGICALFLUARIX QUADRIVALENT
The FDA-approved, quadrivalent seasonal influenza vaccine that will be administered contains four distinct strains, two influenza A viruses and two influenza B viruses.
Sponsors
Emory University
Study design
Allocation
NON_RANDOMIZED
Intervention model
PARALLEL
Primary purpose
BASIC_SCIENCE
Masking
NONE
Eligibility
Sex/Gender
ALL
Age
42 Years to 71 Years
Healthy volunteers
No
Inclusion criteria
1. Capable of informed consent and provision of written informed consent before any study procedures. 2. Capable of attending all study visits according to the study schedule. 3. Males or females born between 1968-1977 or 1948-1957. 4. Are in good health, as determined by medical history and targeted physical exam related to this history. 5. Oral temperature is less than 38 degrees Celsius. 6. Resting pulse rate is between 50 and 100 beats per minute. 7. Female subjects of childbearing age must have a negative urine pregnancy test within 24 hours before study vaccination. 8. Have received the influenza vaccine at least 3 of the past 5 years or have received the influenza vaccine in 2 or less of the past 5 years.
Exclusion criteria
1. Have an acute illness within 72 hours before vaccination. 2. Have any condition that, in the opinion of the principal investigator, would place the subject at an unacceptable risk of harm or confound the interpretation of the study results. 3. Have any acute or chronic medical condition that, in the opinion of the principal investigator, would make vaccination unsafe or interfere with the evaluation of immune response to study vaccination. 4. Have a suppressed immune system as a result of illness, immunosuppressive medication, chemotherapy, or radiation therapy within 3 years prior to study vaccination. 5. Have known HIV, hepatitis B, or hepatitis C infection. 6. Have a known history of autoimmune disease. 7. Have taken oral or parenteral corticosteroids of any dose within 30 days before study vaccination. 8. Have taken high-dose inhaled corticosteroids within 30 days before study vaccination. 9. Have received, or plan to receive, any licensed live vaccine within 30 days, or any licensed inactivated vaccine within 14 days, prior to, or after, study vaccination. 10. Have planned receipt of any unlicensed or investigational medications, biologics, or vaccines for the duration of subject study participation. 11. Have received immunoglobulin or other blood products, with the exception of Rho D immunoglobulin, within 90 days prior to study vaccination. 12. Have donated blood or blood products within 30 days before study vaccination, or within 60 days after study vaccination, or plan to donate blood within 30 days of the last blood draw. 13. Have known hypersensitivity or allergy to eggs, egg protein, chicken protein, or other compounds of the study vaccine. 14. Have a history of severe reactions following vaccination with influenza virus vaccines.
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| The Number of Participants Achieving Seroprotection Against Each Strain | 28 days after vaccination | Seroprotection against each strain contained in the seasonal quadrivalent influenza vaccine (A/H1N1, A/H3N2, B/Phuket, and B/Colorado) were measured by hemagglutination inhibition (HAI) antibody response. Seroprotection is defined as a titer of ≥ 40. |
| The Number of Participants Achieving Seroconversion Against Each Strain | 28 days after vaccination | Seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine was measured by HAI antibody response. Seroconversion is defined as a four-fold rise in HAI post- compared to pre-vaccination, or a titer of ≥40 if the pre-vaccination titer was \<10. |
| Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | 28 days after vaccination | The geometric scale is logarithmic. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| The Number of Participants Achieving Seroconversion Against Each Strain | 180 days after vaccination | Seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine was measured by HAI antibody response. Seroconversion is defined as a four-fold rise in HAI post- compared to pre-vaccination, or a titer of ≥40 if the pre-vaccination titer was \<10. |
| The Proportion of Participants Achieving Seroprotection or Seroconversion Against Each Strain Measured by Neutralizing Antibody (NAb) Response | 28 days after vaccination | Seroprotection/seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine will be measured by neutralizing antibody (NAb) response. The proportion of subjects achieving seroprotection (titer of ≥ 40) or seroconversion (four-fold rise in NAb post- compared to pre-vaccination, or a titer of ≥40 if the pre-vaccination titer was \<10) against each strain will be assessed. |
| The Proportion of Participants Achieving Seroprotection or Seroconversion Against Each Strain Measured by NAb Response | 180 days after vaccination | Seroprotection/seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine will be measured by NAb antibody response. |
| Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | 180 days after vaccination | The geometric scale is logarithmic. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number. |
| Geometric Mean Titers (GMTs) of Serum NAb Against Each Strain | 28 days after vaccination | The geometric scale is logarithmic. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number. |
| The Number of Participants Achieving Seroprotection Against Each Strain | 180 days after vaccination | Seroprotection against each strain contained in the seasonal quadrivalent influenza vaccine (A/H1N1, A/H3N2, B/Phuket, and B/Colorado) were measured by hemagglutination inhibition (HAI) antibody response. Seroprotection is defined as a titer of ≥ 40. |
Countries
United States
Participant flow
Recruitment details
Participant enrollment began October 22, 2018 and all follow up was complete by June 20, 2020. Participants were enrolled at the Hope Clinic of the Emory Vaccine Center in Atlanta, Georgia, USA.
Pre-assignment details
Individuals were permitted to participate in multiple years of the study. One individual belonging to the H1N1 Birth Cohort, born between the years of 1948 and 1957, participated in both the 2018-2019 and 2019-2020 vaccine years. Thus, each vaccine year for this cohort had 10 participants, but there were 19 discrete individuals overall.
Participants by arm
| Arm | Count |
|---|---|
| H3N2 Birth Cohort, Born Between 1968 and 1977 The H3N2 cohort consists of participants who were born between 1968-1977. Participants received the FLUARIX QUADRIVALENT flu vaccine for the 2018-2019 vaccine year or the 2019-2020 vaccine year. The FDA-approved, quadrivalent seasonal influenza vaccine administered contained four distinct strains, two influenza A viruses and two influenza B viruses | 20 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 The H1N1 cohort consists of participants who were born between 1948-1957. Participants received the FLUARIX QUADRIVALENT flu vaccine for the 2018-2019 vaccine year and/or the 2019-2020 vaccine year. The FDA-approved, quadrivalent seasonal influenza vaccine administered contained four distinct strains, two influenza A viruses and two influenza B viruses. | 19 |
| Total | 39 |
Baseline characteristics
| Characteristic | H3N2 Birth Cohort, Born Between 1968 and 1977 | H1N1 Birth Cohort, Born Between 1948 and 1957 | Total |
|---|---|---|---|
| Age, Categorical <=18 years | 0 Participants | 0 Participants | 0 Participants |
| Age, Categorical >=65 years | 0 Participants | 12 Participants | 12 Participants |
| Age, Categorical Between 18 and 65 years | 20 Participants | 7 Participants | 27 Participants |
| Age, Continuous | 45.39 years STANDARD_DEVIATION 2.77 | 66.95 years STANDARD_DEVIATION 2.29 | 55.89 years STANDARD_DEVIATION 11.2 |
| Ethnicity (NIH/OMB) Hispanic or Latino | 0 Participants | 0 Participants | 0 Participants |
| Ethnicity (NIH/OMB) Not Hispanic or Latino | 20 Participants | 19 Participants | 39 Participants |
| Ethnicity (NIH/OMB) Unknown or Not Reported | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) American Indian or Alaska Native | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Asian | 2 Participants | 0 Participants | 2 Participants |
| Race (NIH/OMB) Black or African American | 5 Participants | 3 Participants | 8 Participants |
| Race (NIH/OMB) More than one race | 1 Participants | 0 Participants | 1 Participants |
| Race (NIH/OMB) Native Hawaiian or Other Pacific Islander | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Unknown or Not Reported | 1 Participants | 0 Participants | 1 Participants |
| Race (NIH/OMB) White | 11 Participants | 16 Participants | 27 Participants |
| Region of Enrollment United States | 20 Participants | 19 Participants | 39 Participants |
| Sex: Female, Male Female | 9 Participants | 11 Participants | 20 Participants |
| Sex: Female, Male Male | 11 Participants | 8 Participants | 19 Participants |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk |
|---|---|---|
| deaths Total, all-cause mortality | 0 / 20 | 0 / 19 |
| other Total, other adverse events | 0 / 20 | 0 / 19 |
| serious Total, serious adverse events | 0 / 20 | 0 / 19 |
Outcome results
Primary
Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain
The geometric scale is logarithmic. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number.
Time frame: 28 days after vaccination
Population: The data for the individual in the H1N1 Birth Cohort who participated in both vaccine years is included for each year of participation.
| Arm | Measure | Group | Value (GEOMETRIC_MEAN) | Dispersion |
|---|---|---|---|---|
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H1N1 | 282.5 GMTs | Standard Deviation 301 |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H3N2 | 458 GMTs | Standard Deviation 564 |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Phuket | 463 GMTs | Standard Deviation 579 |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Colorado | 258 GMTs | Standard Deviation 273 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Colorado | 180 GMTs | Standard Deviation 260 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H1N1 | 389 GMTs | Standard Deviation 575 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Phuket | 200 GMTs | Standard Deviation 183 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H3N2 | 539 GMTs | Standard Deviation 1097 |
Primary
The Number of Participants Achieving Seroconversion Against Each Strain
Seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine was measured by HAI antibody response. Seroconversion is defined as a four-fold rise in HAI post- compared to pre-vaccination, or a titer of ≥40 if the pre-vaccination titer was \<10.
Time frame: 28 days after vaccination
Population: The data for the individual in the H1N1 Birth Cohort who participated in both vaccine years is included for each year of participation.
| Arm | Measure | Group | Value (COUNT_OF_PARTICIPANTS) |
|---|---|---|---|
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H1N1 | 11 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H3N2 | 12 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Phuket | 9 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Colorado | 8 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Colorado | 8 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H1N1 | 10 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Phuket | 11 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H3N2 | 10 Participants |
Primary
The Number of Participants Achieving Seroprotection Against Each Strain
Seroprotection against each strain contained in the seasonal quadrivalent influenza vaccine (A/H1N1, A/H3N2, B/Phuket, and B/Colorado) were measured by hemagglutination inhibition (HAI) antibody response. Seroprotection is defined as a titer of ≥ 40.
Time frame: 28 days after vaccination
Population: The data for the individual in the H1N1 Birth Cohort who participated in both vaccine years is included for each year of participation.
| Arm | Measure | Group | Value (COUNT_OF_PARTICIPANTS) |
|---|---|---|---|
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H1N1 | 19 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H3N2 | 20 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Phuket | 19 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Colorado | 20 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Colorado | 20 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H1N1 | 20 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Phuket | 17 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H3N2 | 17 Participants |
Secondary
Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain
The geometric scale is logarithmic. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number.
Time frame: 180 days after vaccination
Population: The data for the individual in the H1N1 Birth Cohort who participated in both vaccine years is included for each year of participation.
| Arm | Measure | Group | Value (GEOMETRIC_MEAN) | Dispersion |
|---|---|---|---|---|
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H1N1 | 151.2 GMTs | Standard Deviation 153 |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H3N2 | 124 GMTs | Standard Deviation 147 |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Phuket | 135 GMTs | Standard Deviation 112 |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Colorado | 130 GMTs | Standard Deviation 157 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Colorado | 98 GMTs | Standard Deviation 67 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H1N1 | 197 GMTs | Standard Deviation 191 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | B/Phuket | 114 GMTs | Standard Deviation 92 |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | Geometric Mean Titers (GMTs) of Serum HAI Against Each Strain | A/H3N2 | 185 GMTs | Standard Deviation 297 |
Secondary
Geometric Mean Titers (GMTs) of Serum NAb Against Each Strain
The geometric scale is logarithmic. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number.
Time frame: 180 days after vaccination
Population: NAb testing was not performed as all research efforts moved to COVID-19 research.
Secondary
Geometric Mean Titers (GMTs) of Serum NAb Against Each Strain
The geometric scale is logarithmic. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number.
Time frame: 28 days after vaccination
Population: NAb testing was not performed as all research efforts moved to COVID-19 research.
Secondary
The Number of Participants Achieving Seroconversion Against Each Strain
Seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine was measured by HAI antibody response. Seroconversion is defined as a four-fold rise in HAI post- compared to pre-vaccination, or a titer of ≥40 if the pre-vaccination titer was \<10.
Time frame: 180 days after vaccination
Population: The data for the individual in the H1N1 Birth Cohort who participated in both vaccine years is included for each year of participation.
| Arm | Measure | Group | Value (COUNT_OF_PARTICIPANTS) |
|---|---|---|---|
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H1N1 | 7 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H3N2 | 5 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Phuket | 4 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Colorado | 3 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Colorado | 7 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H1N1 | 7 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | B/Phuket | 5 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroconversion Against Each Strain | A/H3N2 | 6 Participants |
Secondary
The Number of Participants Achieving Seroprotection Against Each Strain
Seroprotection against each strain contained in the seasonal quadrivalent influenza vaccine (A/H1N1, A/H3N2, B/Phuket, and B/Colorado) were measured by hemagglutination inhibition (HAI) antibody response. Seroprotection is defined as a titer of ≥ 40.
Time frame: 180 days after vaccination
Population: The data for the individual in the H1N1 Birth Cohort who participated in both vaccine years is included for each year of participation.
| Arm | Measure | Group | Value (COUNT_OF_PARTICIPANTS) |
|---|---|---|---|
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H1N1 | 18 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H3N2 | 17 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Phuket | 17 Participants |
| H3N2 Birth Cohort, Born Between 1968 and 1977 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Colorado | 18 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Colorado | 20 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H1N1 | 17 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | B/Phuket | 14 Participants |
| H1N1 Birth Cohort, Born Between 1948 and 1957 | The Number of Participants Achieving Seroprotection Against Each Strain | A/H3N2 | 12 Participants |
Secondary
The Proportion of Participants Achieving Seroprotection or Seroconversion Against Each Strain Measured by NAb Response
Seroprotection/seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine will be measured by NAb antibody response.
Time frame: 180 days after vaccination
Population: NAb testing was not performed as all research efforts moved to COVID-19 research.
Secondary
The Proportion of Participants Achieving Seroprotection or Seroconversion Against Each Strain Measured by Neutralizing Antibody (NAb) Response
Seroprotection/seroconversion against each strain contained in the seasonal quadrivalent influenza vaccine will be measured by neutralizing antibody (NAb) response. The proportion of subjects achieving seroprotection (titer of ≥ 40) or seroconversion (four-fold rise in NAb post- compared to pre-vaccination, or a titer of ≥40 if the pre-vaccination titer was \<10) against each strain will be assessed.
Time frame: 28 days after vaccination
Population: NAb testing was not performed as all research efforts moved to coronavirus disease 2019 (COVID-19) research.