November 26, 2015
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Influenza A H1N1 Monovalent Vaccine

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Influenza A H1N1 Monovalent Vaccine


Mechanism of Action

Influenza illness and its complications follow infection with influenza viruses. Global surveillance of influenza identifies yearly antigenic variants. For example, since 1977, antigenic variants of influenza A (H1N1 and H3N2) viruses and influenza B viruses have been in global circulation. Specific levels of hemagglutinin inhibition (HI) antibody titer post-vaccination with inactivated influenza virus vaccines have not been correlated with protection from influenza virus infection. In some human studies, antibody titer of ≥ 1:40 have been associated with protection from influenza illness in up to 50% of subjects. (4) (5)

Antibodies against one influenza virus type or subtype confer limited or no protection against another. Furthermore, antibodies to one antigenic variant of influenza virus might not protect against a new antigenic variant of the same type or subtype. Frequent development of antigenic

variants through antigenic drift is the virologic basis for seasonal epidemics and the reason for the usual change of one or more new strains in each year's influenza vaccine.

Clinical Studies

Sanofi Pasteur's Influenza A (H1N1) 2009 Monovalent Vaccine and seasonal trivalent Influenza Virus Vaccine (Fluzone vaccine) are manufactured by the same process. Data in this section were obtained in clinical studies conducted with Fluzone vaccine.

Immunogenicity in the Adult and Geriatric Population

In an observational study of the immunogenicity of Fluzone vaccine in a geriatric population (median age: 72.0 range: 61 to 86 years of age) compared with younger adults (median age: 38.0 range: 19 to 59 years of age; racial distribution was 2 Asian, 11 Black, 106 Caucasian, and 2 other; no gender data were available), the following results were obtained using a single-dose of the year 1999–2000 formulation of Fluzone vaccine. (See Table 1.) Antibody levels were obtained on the day of and just prior to vaccination and approximately 21 days after vaccination. (4)

Table 1: Geometric Mean Titer (GMT) and Percentage (%) Achieving an HI Titer ≥ 1:40 (N = 58-62) in Adults and the Elderly (after vaccination with Fluzone vaccine)

(% TITER ≥ 40)
A (H3N2) Cohort 1999 Young
(N = 60)
16.6 53.1 (72)
(N = 61)
20.1 58.2 (70)
Cohort 2000 Young
(N = 58)
18.6 72.7 (79)
(N = 62)
18.1 49.7 (68)
A (H1N1) Cohort 1999 Young
(N = 60)
11.1 35.6 (49)
(N = 61)
12.2 26.5 (38)
Cohort 2000 Young
(N = 58)
8.9 35.9 (54)
(N = 62)
6.7 16.0 (23)
B Cohort 1999 Young
(N = 60)
14.4 41.4 (38)
Elderly (N = 61) 9.9 19.4 (10)
Cohort 2000 Young
(N = 58)
9.4 21.5 (38)
(N = 62)
7.4 9.9 (11)
N = Number of participants

Immunogenicity in Children

In a study using 2 doses of Fluzone vaccine (2003-2004) in 31 healthy children 6–36 months of age (3 Black, 23 Caucasian, 2 Hispanic, and 3 other; 15 were male and 16 were female), the following immunogenicity results were obtained on day 0 before vaccination and approximately 14 days after dose number 2. (See Table 2.)

Table 2: Geometric Mean Titer (GMT) and Percentage (%) Achieving an HI Titer of ≥ 1:40 in Children (after vaccination with Fluzone vaccine)

(% TITER ≥ 40)
A (H3N2) 7.7 52.9 (77.4)
A (H1N1) 6.5 52.9 (77.4)
B 5.2 27.3 (48.4)


1. Centers for Disease Control and Prevention. Serum Cross-Reactive Antibody Response to a Novel Influenza A (H1N1) Virus After Vaccination with Seasonal Influenza Vaccine. MMWR 2009;58(19):521-524.

2. Centers for Disease Control and Prevention. Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2009;58(RR08):1-52.

3. Sanofi Pasteur Inc. Data on file, 071107.

4. Hannoun C et al. Immunogenicity and protective efficacy of influenza vaccination. Virus Res 2004;103:133-138

5. Hobson D, et al. The role of serum hemagglutinin-inhibiting antibody in protection against challenge infection with influenza A2 and B viruses J Hyg Camb 1972;70:767-777.

Last reviewed on RxList: 11/5/2009
This monograph has been modified to include the generic and brand name in many instances.

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