CLINICAL PHARMACOLOGY
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 hemagglutination 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 titers ≥ 1:40 have been associated with protection from
influenza illness in up to 50% of participants. (See references 3 and 4.)
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. Therefore, influenza vaccines are standardized to contain the
hemagglutinins of influenza virus strains representing the influenza viruses
likely to be circulating in the US during the influenza season.
Annual vaccination with the current vaccine is
recommended because immunity during the year after vaccination declines and
because circulating strains of influenza virus change from year to year.
Clinical Studies
Immunogenicity Of Fluzone High-Dose In Adults 65 Years Of
Age And Older
Study 1 (NCT00391053) was a multi-center, double-blind
pre-licensure trial conducted in the US in which adults 65 years of age and
older were randomized to receive either Fluzone High-Dose or Fluzone (2006-2007
formulation). The study compared the safety and immunogenicity of Fluzone
High-Dose to those of Fluzone. For immunogenicity analyses, 2576 participants
were randomized to Fluzone High-Dose and 1275 participants were randomized to
Fluzone. Females accounted for 51.3% of participants in the Fluzone High-Dose
group and 54.7% of participants in the Fluzone group. In both groups, the mean age
was 72.9 years (ranged from 65 through 97 years in the Fluzone High-Dose group
and 65 through 94 years in the Fluzone group); 35% of participants in the
Fluzone High-Dose group and 36% of participants in the Fluzone group were 75
years of age or older. Most participants in the Fluzone High-Dose and Fluzone
groups, respectively, were White (91.7% and 92.9%), followed by Hispanic (4.8%
and 3.7%), and Black (2.7% and 2.7%).
The primary endpoints of the study were HI GMTs and
seroconversion rates 28 days after vaccination. Pre-specified statistical
superiority criteria required that the lower limit (LL) of the 2-sided 95% CI
of the GMT ratio (Fluzone High-Dose/Fluzone) be greater than 1.50 for at least
two of the strains, and if one strain failed, non-inferiority of that strain must
be demonstrated (LL > 0.67), and that the lower limit of the 2-sided 95% CI of
the seroconversion rate difference (Fluzone High-Dose minus Fluzone) be greater
than 10% for at least two of the strains, and if one strain failed,
non-inferiority of that strain must be demonstrated (LL > -10%). As shown in
Table 3, statistically superior HI GMTs and seroconversion rates after
vaccination with Fluzone High-Dose compared to Fluzone were demonstrated for
influenza A subtypes, A (H1N1) and A (H3N2), but not for influenza type B. For
strain B, non-inferiority of Fluzone High-Dose compared to Fluzone was
demonstrated for both the HI GMTs and seroconversion rates.
Table 3: Study 1a: Post-Vaccination HI
Antibody GMTs and Seroconversion Rates and Analyses of Superiority of Fluzone
High-Dose Relative to Fluzone, Adults 65 Years of Age and Older
Influenza Strain |
GMT |
GMT Ratio |
Seroconversion %b |
Difference |
Met Both Pre-defined Superiority Criteriad |
Fluzone High- Dose
Nc=2542- 2544 |
Fluzone
Nc=1252 |
Fluzone High-Dose over Fluzone (95% CI) |
Fluzone High-Dose
Nc=2529- 2531 |
Fluzone
Nc=1248- 1249 |
Fluzone High-Dose minus Fluzone (95% CI) |
A (H1N1) |
115.8 |
67.3 |
1.7
(1.6; 1.8) |
48.6 |
23.1 |
25.4
(22.4; 28.5) |
Yes |
A (H3N2) |
608.9 |
332.5 |
1.8
(1.7; 2.0) |
69.1 |
50.7 |
18.4
(15.1; 21.7) |
Yes |
B |
69.1 |
52.3 |
1.3
(1.2; 1.4) |
41.8 |
29.9 |
11.8
(8.6; 15.0) |
No |
a NCT00391053
b Seroconversion: Paired samples with pre-vaccination HI titer
< 1:10 and post-vaccination (day 28) titer ≥ 1:40 or a minimum 4-fold
increase for participants with pre-vaccination titer ≥ 1:10
c N is the number of vaccinated participants with available data for
the immunologic endpoint listed
d Predefined superiority criterion for seroconversion: the lower
limit of the two-sided 95% CI of the difference of the seroconversion rates
(Fluzone High-Dose minus Fluzone) is > 10%. Predefined superiority criterion
for the GMT ratio: the lower limit of the 95% CI of the GMT ratio (Fluzone
High-Dose divided by Fluzone) is > 1.5 |
Efficacy Of Fluzone High-Dose In Adults 65 Years Of Age And
Older
Study 2 (NCT01427309) was a multi-center, double-blind
post-licensure efficacy trial conducted in the US and Canada in which adults 65
years of age and older were randomized (1:1) to receive either Fluzone
High-Dose or Fluzone. The study was conducted over two influenza seasons
(2011-2012 and 2012-2013); 53% of participants enrolled in the first year of
the study were re-enrolled and re-randomized in the second year. The per-protocol
analysis set for efficacy assessments included 15,892 Fluzone High-Dose recipients
and 15,911 Fluzone recipients. The majority (67%) of participants in the
perprotocol analysis set for efficacy had one or more high-risk chronic
comorbid conditions.
In the per-protocol analysis set, females accounted for
57.2% of participants in the Fluzone High-Dose group and 56.1% of participants
in the Fluzone group. In both groups, the median age was 72.2 years (range 65
through 100 years). Overall, most participants in the study were White (95%);
approximately 4% of study participants were Black, and approximately 6%
reported Hispanic ethnicity.
The primary endpoint of the study was the occurrence of
laboratory-confirmed influenza (as determined by culture or polymerase chain
reaction) caused by any influenza viral type/ subtype in association with
influenza-like illness (ILI), defined as the occurrence of at least one of the
following respiratory symptoms: sore throat, cough, sputum production,
wheezing, or difficulty breathing; concurrent with at least one of the
following systemic signs or symptoms: temperature > 99.0°F, chills,
tiredness, headaches or myalgia. Participants were monitored for the occurrence
of a respiratory illness by both active and passive surveillance, starting 2
weeks post-vaccination for approximately 7 months. After an episode of respiratory
illness, nasopharyngeal swab samples were collected for analysis; attack rates and
vaccine efficacy were calculated (see Table 4).
Table 4: Study 2a: Relative Efficacy
Against Laboratory-Confirmed Influenzab Regardless of Similarity to
the Vaccine Components, Associated with Influenza-Like Illnessc, Adults 65
Years of Age and Older
|
Fluzone High-Dose
Nd=15,892 ne (%) |
Fluzone
Nd=15,911 ne (%) |
Relative Efficacy % (95% CI) |
Any type/ subtypef |
227 (1.43) |
300 (1.89) |
24.2 (9.7; 36.5)g |
Influenza A |
190 (1.20) |
249 (1.56) |
23.6 (7.4; 37.1) |
A (H1N1) |
8 (0.05) |
9 (0.06) |
11.0 (-159.9; 70.1) |
A (H3N2) |
171 (1.08) |
222 (1.40) |
22.9 (5.4; 37.2) |
Influenza Bh |
37 (0.23) |
51 (0.32) |
27.4 (-13.1; 53.8) |
a NCT01427309
b Laboratory-confirmed: culture- or
polymerase-chain-reaction-confirmed
c Occurrence of at least one of the following respiratory symptoms:
sore throat, cough, sputum production, wheezing, or difficulty breathing;
concurrent with at least one of the following systemic signs or symptoms:
temperature > 99.0°F, chills, tiredness, headaches or myalgia
d N is the number of vaccinated participants in the per-protocol
analysis set for efficacy assessments
e n is the number of participants with protocol-defined
influenza-like illness with laboratory confirmation
f Primary endpoint
g The pre-specified statistical superiority criterion for the
primary endpoint (lower limit of the 2-sided 95% CI of the vaccine efficacy of
Fluzone High-Dose relative to Fluzone > 9.1%) was met.
h In the first year of the study the influenza B component of the
vaccine and the majority of influenza B cases were of the Victoria lineage; in
the second year the influenza B component of the vaccine and the majority of
influenza B cases were of the Yamagata lineage |
A secondary endpoint of the study was the occurrence of
culture-confirmed influenza caused by viral types/subtypes antigenically
similar to those contained in the respective annual vaccine formulations in
association with a modified CDC-defined ILI, defined as the occurrence of a
temperature > 99.0°F ( > 37.2°C) with cough or sore throat. The efficacy
of Fluzone High-Dose relative to Fluzone for this endpoint was 51.1% (95% CI:
16.8; 72.0).
REFERENCES
3 Hannoun C, Megas F, Piercy J. Immunogenicity and
protective efficacy of influenza vaccination. Virus Res 2004;103:133-138.
4 Hobson D, Curry RL, Beare AS, Ward-Gardner A. The role
of serum haemagglutination-inhibiting antibody in protection against challenge
infection with influenza A2 and B viruses. J Hyg Camb 1972;70:767-777.