CLINICAL PHARMACOLOGY
Mechanism Of Action
Immune mechanisms conferring protection against influenza
following receipt of FluMist Quadrivalent vaccine are not fully understood;
serum antibodies, mucosal antibodies, and influenza-specific T cells may play a
role.
FluMist and FluMist Quadrivalent contain live attenuated
influenza viruses that must infect and replicate in cells lining the
nasopharynx of the recipient to induce immunity. Vaccine viruses capable of
infection and replication can be cultured from nasal secretions obtained from
vaccine recipients (shedding) [see Pharmacodynamics].
Pharmacodynamics
Shedding Studies
Shedding of vaccine viruses within 28 days of vaccination
with FluMist was evaluated in (1) multi-center study MI-CP129 which enrolled
healthy individuals 6 through 59 months of age (N = 200); and (2) multi-center
study FM026 which enrolled healthy individuals 5 through 49 years of age (N =
344). In each study, nasal secretions were obtained daily for the first 7 days
and every other day through either Day 25 and on Day 28 or through Day 28. In
study MI-CP129, individuals with a positive shedding sample at Day 25 or Day 28
were to have additional shedding samples collected every 7 days until culture
negative on 2 consecutive samples. Results of these studies are presented in
Table 5.
Table 5: Characterization of Shedding with FluMist in
Specified Age Groups by Frequency, Amount, and Duration (Study MI-CP129a
and Study FM026b)
Age |
Number of Subjects |
Sheddingc |
Peak Titer (TCID50/mL)d |
Shedding After Day 11 |
Day of Last Positive Culture |
6-23 monthse |
99 |
89 |
< 5 log10 |
7.0 |
Day 23f |
24-59 months |
100 |
69 |
< 5 log10 |
1.0 |
Day 25g |
5-8 years |
102 |
50 |
< 5 log10 |
2.9 |
Day 23h |
9-17 years |
126 |
29 |
< 4 log10 |
1.6 |
Day 28h |
18-49 years |
115 |
20 |
< 3 log10 |
0.9 |
Day 17h |
a NCT00344305; see www.clinicaltrials.gov
b NCT00192140; see www.clinicaltrials.gov
c Proportion of subjects with detectable virus at any time point
during the 28 days.
d Peak titer at any time point during the 28 days among samples
positive for a single vaccine virus.
e FluMist and FluMist Quadrivalent are not approved for use in
children younger than 24 months of age [see ADVERSE REACTIONS].
f A single subject who shed previously on Days 1-3; TCID50/mL was
less than 1.5 log10 on Day 23.
g A single subject who did not shed previously; TCID50/mL was less
than 1.5 log10.
h A single subject who did not shed previously; TCID50/mL was less
than 1.0 log10. |
The highest proportion of subjects in each group shed one
or more vaccine strains on Days 2-3 post vaccination. After Day 11 among
individuals 2 through 49 years of age (n = 443), virus titers did not exceed
1.5 log10 TCID50/mL.
Studies In Immunocompromised Individuals
Safety and shedding of vaccine virus following FluMist
administration were evaluated in 28 HIV-infected adults [median CD4 cell count
of 541 cells/mm³] and 27 HIV-negative adults 18 through 58 years of age. No
serious adverse events were reported during the one-month follow-up period.
Vaccine strain (type B) virus was detected in 1 of 28 HIV-infected subjects on
Day 5 only, and in none of the HIV-negative FluMist recipients.
Safety and shedding of vaccine virus following FluMist
administration were also evaluated in children in a randomized (1:1),
cross-over, double-blind, AF-SPG placebo-controlled trial in 24 HIV-infected
children [median CD4 cell count of 1013 cells/mm³] and 25 HIV-negative children
1 through 7 years of age, and in a randomized (1:1), open-label, inactivated
influenza vaccine-controlled trial in 243HIV-infected children and adolescents
5 through 17 years of age receiving stable anti-retroviral therapy. Frequency
and duration of vaccine virus shedding in HIV-infected individuals were
comparable to that seen in healthy individuals. No adverse effects on HIV viral
load or CD4 counts were identified following FluMist administration. In the 5
through 17 year old age group, one inactivated influenza vaccine recipient and
one FluMist recipient experienced pneumonia within 28 days of vaccination (days
17 and 13, respectively). The effectiveness of FluMist and FluMist Quadrivalent
in preventing influenza illness in HIV-infected individuals has not been
evaluated.
Twenty mild to moderately immunocompromised children and
adolescents 5 through 17 years of age (receiving chemotherapy and/or radiation
therapy or who had received chemotherapy in the 12 weeks prior to enrollment)
were randomized 1:1 to receive FluMist or AF-SPG placebo. Frequency and
duration of vaccine virus shedding in these immunocompromised children and
adolescents were comparable to that seen in healthy children and adolescents.
The effectiveness of FluMist and FluMist Quadrivalent in preventing influenza
illness in immunocompromised individuals has not been evaluated.
Transmission Study
A prospective, randomized, double-blind, placebo-controlled
trial was performed in a daycare setting in children younger than 3 years of
age to assess the transmission of vaccine viruses from a vaccinated individual
to a non-vaccinated individual. A total of 197 children 8 through 36 months of
age were randomized to receive one dose of FluMist (N = 98) or AF-SPG placebo
(N = 99). Virus shedding was evaluated for 21 days by culture of nasal swab
specimens. Wild-type A (A/H3N2) influenza virus was documented to have
circulated in the community and in the study population during the trial,
whereas Type A (A/H1N1) and Type B strains did not.
At least one vaccine strain was isolated from 80% of
FluMist recipients; strains were recovered from 1-21 days post vaccination
(mean duration of 7.6 days ± 3.4 days). The cold-adapted (ca) and
temperature-sensitive (ts) phenotypes were preserved in 135 tested of 250
strains isolated at the local laboratory. Ten influenza isolates (9 influenza
A, 1 influenza B) were cultured from a total of seven placebo subjects. One
placebo subject had mild symptomatic Type B virus infection confirmed as a
transmitted vaccine virus by a FluMist recipient in the same playgroup. This
Type B isolate retained the ca, ts, and att phenotypes of the vaccine strain
and had the same genetic sequence when compared to a Type B virus cultured from
a vaccine recipient within the same playgroup. Four of the influenza Type A
isolates were confirmed as wild-type A/Panama (H3N2). The remaining isolates
could not be further characterized.
Assuming a single transmission event (isolation of the
Type B vaccine strain), the probability of a young child acquiring vaccine
virus following close contact with a single FluMist vaccinee in this daycare
setting was 0.58% (95% CI: 0, 1.7) based on the Reed-Frost model. With documented
transmission of one Type B in one placebo subject and possible transmission of
Type A viruses in four placebo subjects, the probability of acquiring a
transmitted vaccine virus was estimated to be 2.4% (95% CI: 0.13, 4.6) using
the Reed-Frost model.
Pharmacokinetics
Biodistribution
A biodistribution study of intranasally administered
radiolabeled placebo was conducted in 7 healthy adult volunteers. The mean
percentages of the delivered doses detected were as follows: nasal cavity
89.7%, stomach 2.6%, brain 2.4%, and lung 0.4%. The clinical significance of
these findings is unknown.
Clinical Studies
The effectiveness of FluMist Quadrivalent is based on
data demonstrating the clinical efficacy of FluMist in children and the
effectiveness of FluMist in adults, and a comparison of post vaccination
geometric mean titers (GMTs) of hemagglutination inhibition (HI) antibodies
between individuals receiving FluMist and FluMist Quadrivalent. The clinical
experience with FluMist is relevant to FluMist Quadrivalent because both
vaccines are manufactured using the same process and have overlapping
compositions [see DESCRIPTION].
Efficacy Studies Of FluMist In Children And Adolescents
A multinational, randomized, double-blind,
active-controlled trial (MI-CP111) was performed to assess the efficacy of
FluMist compared to an intramuscularly administered, inactivated Influenza
Virus Vaccine manufactured by Sanofi Pasteur Inc. (active control) in children
6 months to less than 5 years of age during the 2004-2005 influenza season. A
total number of 3916 children without severe asthma, without use of
bronchodilator or steroids, and without wheezing within the prior 6 weeks were
randomized to FluMist and 3936 were randomized to active control. Children who
previously received any influenza vaccine received a single dose of study
vaccine, while those who never previously received an influenza vaccination (or
had an unknown history of influenza vaccination) received two doses.
Participants were then followed through the influenza season to identify illness
caused by influenza virus. As the primary endpoint, culture-confirmed modified
CDC-ILI (CDC-defined influenza-like illness) was defined as a positive culture
for a wild-type influenza virus associated within ±7 days of modified CDC-ILI.
Modified CDC-ILI was defined as fever (temperature ≥ 100°F oral or
equivalent) with cough, sore throat, or runny nose/nasal congestion on the same
or consecutive days.
In the primary efficacy analysis, FluMist demonstrated a
44.5% (95% CI: 22.4, 60.6) reduction in influenza rate compared to active
control as measured by culture-confirmed modified CDC-ILI caused by wild-type
strains antigenically similar to those contained in the vaccine. See Table 6
for a description of the results by strain and antigenic similarity.
Table 6: Comparative Efficacy Against
Culture-Confirmed Modified CDC-ILIa Caused by Wild-Type Strains
(Study MI-CP111)b,c
|
FluMist |
Active Controld |
% Reduction inRate for FluMiste |
95% CI |
N |
# of Cases |
Rate (cases/N) |
N |
# of Cases |
Rate (cases/N) |
Matched Strains |
All strains |
3916 |
53 |
1.4% |
3936 |
93 |
2.4% |
44.5% |
22.4, 60.6 |
A/H1N1 |
3916 |
3 |
0.1% |
3936 |
27 |
0.7% |
89.2% |
67.7, 97.4 |
A/H3N2 |
3916 |
0 |
0.0% |
3936 |
0 |
0.0% |
-- |
-- |
B |
3916 |
50 |
1.3% |
3936 |
67 |
1.7% |
27.3% |
-4.8, 49.9 |
Mismatched Strains |
All strains |
3916 |
102 |
2.6% |
3936 |
245 |
6.2% |
58.2% |
47.4, 67.0 |
A/H1N1 |
3916 |
0 |
0.0% |
3936 |
0 |
0.0% |
-- |
-- |
A/H3N2 |
3916 |
37 |
0.9% |
3936 |
178 |
4.5% |
79.2% |
70.6, 85.7 |
B |
3916 |
66 |
1.7% |
3936 |
71 |
1.8% |
6.3% |
-31.6,33.3 |
Regardless of Match |
All strains |
3916 |
153 |
3.9% |
3936 |
338 |
8.6% |
54.9% |
45.4, 62.9 |
A/H1N1 |
3916 |
3 |
0.1% |
3936 |
27 |
0.7% |
89.2% |
67.7, 97.4 |
A/H3N2 |
3916 |
37 |
0.9% |
3936 |
178 |
4.5% |
79.2% |
70.6, 85.7 |
B |
3916 |
115 |
2.9% |
3936 |
136 |
3.5% |
16.1% |
-7.7, 34.7 |
ATP Population.
a Modified CDC-ILI
was defined as fever (temperature ≥ 100°F
oral or equivalent) plus cough, sore throat, or runny nose/nasal congestion on
the same or consecutive days.
b In children 6
months through 5 years of age
c NCT00128167;
see www.clinicaltrials.gov
d Inactivated
Influenza Virus Vaccine manufactured by Sanofi Pasteur Inc., administered
intramuscularly.
e Reduction in rate
was adjusted for country, age, prior influenza vaccination status, and wheezing
history status. |
A randomized, double-blind, saline placebo-controlled
trial (D153-P501) was performed to evaluate the efficacy of FluMist in children
12 through 35 months of age without high-risk medical conditions against
culture-confirmed influenza illness. This study was performed in Asia over two
successive seasons (2000-2001 and 2001-2002). The primary endpoint of the trial
was the prevention of culture-confirmed influenza illness due to antigenically
matched wild-type influenza. Respiratory illness that prompted an influenza
culture was defined as at least one of the following: fever ( ≥ 100.4°F
rectal or ≥ 99.5°F axillary), wheezing, shortness of breath, pulmonary
congestion, pneumonia, or otitis media; or two of the following: runny nose/nasal
congestion, sore throat, cough, muscle aches, chills, headache, irritability,
decreased activity, or vomiting. A total of 3174 children were randomized 3:2
(vaccine: placebo) to receive 2 doses of study vaccine or placebo at least 28
days apart in Year 1. See Table 7 for a description of the results.
During the second year of Study D153-P501, for children who
received two doses in Year 1 and one dose in Year 2, FluMist demonstrated 84.3%
(95% CI: 70.1, 92.4) efficacy against culture-confirmed influenza illness due
to antigenically matched wild-type influenza.
Study AV006 was a second multi-center, randomized,
double-blind, AF-SPG placebo-controlled trial performed in U.S. children
without high-risk medical conditions to evaluate the efficacy of FluMist
against culture-confirmed influenza over two successive seasons (1996-1997 and
1997-1998). The primary endpoint of the trial was the prevention of
culture-confirmed influenza illness due to antigenically matched wild-type
influenza in children who received two doses of vaccine in the first year and a
single revaccination dose in the second year. Respiratory illness that prompted
an influenza culture was defined as at least one of the following: fever ( ≥
101°F rectal or oral; or ≥ 100.4°F axillary), wheezing, shortness of
breath, pulmonary congestion, pneumonia, or otitis media; or two of the
following: runny nose/nasal congestion, sore throat, cough, muscle aches,
chills, headache, irritability, decreased activity, or vomiting. During the
first year of the study, 1602 children 15 through 71 months of age were
randomized 2:1 (vaccine: placebo). See Table 7 for a description of the
results.
Table 7: Efficacya of FluMist vs. Placebo
Against Culture-Confirmed Influenza Illness Due to Antigenically Matched Wild-Type
Strains (Studies D153-P501b & AV006c, Year 1)
|
D153-P501d |
AV006e |
FluMist nf (%) |
Placebo nf (%) |
% Efficacy (95% CI) |
FluMist nf (%) |
Placebo nf (%) |
% Efficacy (95% CI) |
Ng = 1653 |
Ng = 1111 |
|
Ng = 849 |
Ng = 410 |
|
Any strain |
56 (3.4%) |
139 (12.5%) |
72.9%h
(62.8, 80.5) |
10 (1%) |
73 (18%) |
93.4%
(87.5, 96.5) |
A/H1N1 |
23 (1.4%) |
81 (7.3%) |
80.9%
(69.4, 88.5)i |
0 |
0 |
-- |
A/H3N2 |
4 (0.2%) |
27 (2.4%) |
90.0%
(71.4, 97.5) |
4 (0.5%) |
48 (12%) |
96.0%
(89.4, 98.5) |
B |
29 (1.8%) |
35 (3.2%) |
44.3%
(6.2, 67.2) |
6 (0.7%) |
31 (7%) |
90.5%
(78.0, 95.9) |
a D153-P501 and AV006 data are for subjects
who received two doses of study vaccine.
b In children 12 through 35 months of age
c In children 15 through 71 months of age
d NCT00192244; see www.clinicaltrials.gov
e NCT00192179; see www.clinicaltrials.gov
f Number and percent of subjects in per-protocol efficacy analysis
population with culture-confirmed influenza illness.
g Number of subjects in per-protocol efficacy analysis population of
each treatment group of each study for the “any strain” analysis.
h For D153-P501, influenza circulated through 12 months following
vaccination.
i Estimate includes A/H1N1 and A/H1N2 strains. Both were considered
antigenically similar to the vaccine. |
During the second year of Study AV006, children remained
in the same treatment group as in Year 1and received a single dose of FluMist
or placebo. During the second year, the primary circulating strain was the
A/Sydney/05/97 H3N2 strain, which was antigenically dissimilar from the H3N2
strain represented in the vaccine, A/Wuhan/359/95; FluMist demonstrated 87.0%
(95% CI: 77.0, 92.6) efficacy against culture-confirmed influenza illness.
Immune Response Study Of FluMist Quadrivalent In Children
And Adolescents
A multicenter, randomized, double-blind,
active-controlled, non-inferiority study (MI-CP208) was performed to assess the
immunogenicity of FluMist Quadrivalent compared to FluMist (active control) in
children and adolescents 2 through 17 years of age. A total of 2312 subjects
were randomized by site at a 3:1:1 ratio to receive either FluMist Quadrivalent
or one of two formulations of comparator vaccine FluMist, each containing a B
strain that corresponded to one of the two B strains in FluMist Quadrivalent (a
B strain of the Yamagata lineage or a B strain of the Victoria lineage).
Children 2 through 8 years of age received 2 doses of
vaccine approximately 30 days apart; children 9 years of age and older received
1 dose. For children 2 through 8 years of age with a history of influenza
vaccination, immunogenicity assessments were performed prior to vaccination and
at 28 days after the first dose. For children 2 through 8 years of age without
a history of influenza vaccination, immunogenicity assessments were performed
prior to vaccination and 28 days after the second dose. For children 9 years of
age and older, immunogenicity assessments were performed prior to vaccination
and at 28 days post vaccination.
Immunogenicity was evaluated by comparing the 4
strain-specific serum hemagglutination inhibition (HAI) antibody geometric mean
titers (GMTs) post dosing and provided evidence that the addition of the second
B strain did not result in immune interference to other strains included in the
vaccine.
Effectiveness Study Of FluMist In Adults
AV009 was a U.S. multi-center, randomized, double-blind,
AF-SPG placebo-controlled trial to evaluate effectiveness of FluMist in adults
18 through 64 years of age without high-risk medical conditions over the
1997-1998 influenza season. Participants were randomized 2:1 (vaccine:
placebo). Cultures for influenza virus were not obtained from subjects in the
trial, thus efficacy against culture-confirmed influenza was not assessed. The
A/Wuhan/359/95 (H3N2) strain, which was contained in FluMist, was antigenically
distinct from the predominant circulating strain of influenza virus during the
trial period, A/Sydney/05/97 (H3N2). Type A/Wuhan (H3N2) and Type B strains
also circulated in the U.S. during the study period. The primary endpoint of
the trial was the reduction in the proportion of participants with one or more
episodes of any febrile illness, and prospective secondary endpoints were
severe febrile illness and febrile upper respiratory illness. Effectiveness for
any of the three endpoints was not demonstrated in a subgroup of adults 50
through 64 years of age. Primary and secondary effectiveness endpoints from the
age group 18 through 49 years are presented in Table 8. Effectiveness was not
demonstrated for the primary endpoint in adults 18 through 49 years of age.
Table 8: Effectiveness of FluMist to Prevent Febrile
Illness in Adults 18 through 49 Years of Age During the 7-Week Site-Specific
Outbreak Period (Study AV009)
Endpoint |
FluMist
N = 2411a n (%) |
Placebo
N = 1226a n (%) |
Percent Reduction |
(95% CI) |
Participants with one or more events of:b |
Primary Endpoint: |
Any febrile illness |
331 (13.73) |
189 (15.42) |
10.9 |
(-5.1, 24.4) |
Secondary Endpoints: |
Severe febrile illness |
250 (10.37) |
158 (12.89) |
19.5 |
(3.0, 33.2) |
Febrile upper respiratory illness |
213 (8.83) |
142 (1 1.58) |
23.7 |
(6.7, 37.5) |
a Number of evaluable subjects (92.7% and
93.0% of FluMist and placebo recipients, respectively).
b The predominantly circulating virus during the trial period was
A/Sydney/05/97 (H3N2), an antigenic variant not included in the vaccine. |
Effectiveness was shown in a post-hoc analysis using an
endpoint of CDC-ILI in the age group 18 through 49 years of age.
Immune Response Study Of FluMist Quadrivalent In Adults
A multicenter, randomized, double-blind,
active-controlled, and non-inferiority study (MI-CP185) was performed to assess
the safety and immunogenicity of FluMist Quadrivalent compared to those of
FluMist (active control) in adults 18 through 49 years of age. A total of 1800
subjects were randomized by site at a 4:1:1 ratio to receive either 1 dose of
FluMist Quadrivalent or 1 dose of one of two formulations of comparator
vaccine, FluMist, each containing a B strain that corresponded to one of the
two B strains in FluMist Quadrivalent (a B strain of the Yamagata lineage and a
B strain of the Victoria lineage).
Immunogenicity in study MI-CP185 was evaluated by
comparing the 4 strain-specific serum hemagglutination inhibition (HAI)
antibody geometric mean titers (GMTs) post dosing and provided evidence that
the addition of the second B strain did not result in immune interference to
other strains included in the vaccine.
Concomitantly Administered Live Virus Vaccines
In Study AV018, concomitant administration of FluMist,
MMR (manufactured by Merck & Co., Inc.) and Varicella Virus Vaccine Live
(manufactured by Merck & Co., Inc.) was studied in 1245 subjects 12 through
15 months of age. Subjects were randomized in a 1:1:1 ratio to MMR, Varicella
vaccine and AF-SPG placebo (group 1); MMR, Varicella vaccine and FluMist (group
2); or FluMist alone (group 3). Immune responses to MMR and Varicella vaccines
were evaluated 6 weeks post-vaccination while the immune responses to FluMist
were evaluated 4 weeks after the second dose. No evidence of interference with
immune response to measles, mumps, rubella, varicella and FluMist vaccines was
observed.
REFERENCES
1. Lasky T, Terracciano GJ, Magder L, et al. The
Guillain-Barré syndrome and the 1992 - 1993 and 1993 - 1994 influenza vaccines.
N Engl J Med 1998;339(25):1797-802.