BQ Journal Vol 53 - Q4 2023 - 25

Morbidity and Mortality Weekly Report
components (control group) (24). Efficacy findings were based
on analyses of data collected during August 2021-January
2023, which included one complete RSV season for Northern
and Southern Hemisphere participants and a partial second
season for Northern Hemisphere participants only. Efficacy
analyses for season one spanned August 2021-October
2022, while efficacy analyses for season two spanned July
2022-January 2023; exact study-defined season dates were
site-dependent. Mean follow-up time from vaccination to end
of efficacy follow-up across both seasons, including a gap in
RSV surveillance between the first and second RSV seasons,
was approximately 12 months per participant.
Efficacy of 1 dose of the Pfizer vaccine in preventing symptomatic,
laboratory-confirmed RSV-associated LRTD††† was
88.9% (95% CI = 53.6%-98.7%) during the first RSV season
and 78.6% (95% CI = 23.2%-96.1%) during the partial
second season (Table 3).§§§ Efficacy of a single dose over two
seasons was 84.4% (95% CI = 59.6%-95.2%) in preventing
RSV-associated LRTD and 81.0% (95% CI = 43.5%-95.2%)
in preventing medically attended RSV-associated LRTD.¶¶¶
The study was not powered to estimate efficacy against hospitalization
(intervention group = one event; control group
= three events), severe RSV illness requiring respiratory support
(intervention group = one event; control group = one
event),**** or death (no events).††††
Evidence regarding safety of the Pfizer vaccine consisted of
data from two randomized, double-blind, placebo-controlled
clinical trials, including the same ongoing phase 3 trial (24),
and a phase 1/2 trial with 91 participants aged ≥65 years who
received either the vaccine formulation used in phase 3 or
placebo (25). Across both clinical trials, severe reactogenicity
events (grade 3 or higher local or systemic reactions recorded
during days 0-7 after vaccination) occurred in 1.0% of the
intervention group participants, compared with 0.7% of the
††† RSV-associated LRTD (RSVpreF trial): the trial had two co-primary endpoints,
defined as RSV lower respiratory tract illness (LRTI) with two or more lower
respiratory signs or three or more lower respiratory symptoms (including new
or worsened cough, sputum production, wheezing, shortness of breath, and
tachypnea) lasting >1 day. For RSVpreF estimates in this report, LRTD refers
to the RSVpreF trial endpoint of LRTI with three or more signs or symptoms.
§§§ Manufacturer-calculated efficacy. Includes events occurring >14 days after
injection and person-time available from the manufacturer's pivotal
phase 3 trial. Estimates are not adjusted.
¶¶¶ Medically attended RSV-associated LRTD (RSVpreF trial): LRTD prompting
any health care visit. Estimates not included in per-protocol assessments.
**** Severe RSV illness requiring respiratory support (RSVpreF trial): RSVassociated
acute respiratory illness with new or increased oxygen
supplementation or mechanical ventilation.
†††† The limited number of hospitalizations, severe RSV illnesses, and deaths
observed in the trial might have been partially due to limited enrollment
of persons at highest risk for RSV disease including those who were frail,
of advanced age, and those living in long-term care facilities and the
exclusion of persons with immune compromise. The 2021-22 RSV season
was also disrupted by the COVID-19 pandemic, and RSV incidence was
lower than expected based on prepandemic surveillance studies.
796
US Department of Health and Human Services | Centers for Disease Control and Prevention | MMWR | July 21, 2023 | Vol. 72 | No. 29
Diagnostics I Pharmaceuticals I DxRx Solutions I Continuing Education I News
BIOTHERAPEUTICS
25
A
PUBLICATION
TABLE 3. Efficacy of 1 dose of Pfizer respiratory syncytial virus RSVpreF
vaccine against respiratory syncytial virus-associated disease among
adults aged ≥60 years - multiple countries, 2021-2023
Vaccine efficacy against outcome, % (95% CI)*
RSV-associated
Efficacy evaluation
period
Season 1¶
Season 2 (interim)**
Combined seasons 1 and 2
(interim)§§
RSV-associated
LRTD†
88.9 (53.6-98.7)
78.6 (23.2-96.1)
84.4 (59.6-95.2)
medically attended
LRTD§
84.6 (32.0-98.3)
-††
81.0 (43.5-95.2)
Abbreviations: LRTD = lower respiratory tract disease; LRTI = lower respiratory
tract illness; RSV = respiratory syncytial virus.
* Manufacturer-calculated efficacy. Includes events >14 days after injection
and person-time available from the manufacturer's pivotal phase 3 trial.
Estimates are unadjusted.
† The RSVpreF trial had two co-primary endpoints, defined as RSV LRTI with
two or more lower respiratory signs or symptoms lasting >1 day, and RSV
LRTI with three or more lower respiratory signs or symptoms lasting >1 day.
Lower respiratory signs and symptoms included new or worsened cough,
sputum production, wheezing, shortness of breath, and tachypnea. For
RSVpreF estimates in this report, LRTD refers to the RSVpreF trial endpoint
of RSV LRTI with three or more lower respiratory signs or symptoms.
§ Medically attended RSV-associated LRTD was defined as LRTD prompting
any health care visit (any outpatient or inpatient visit such as hospitalization,
emergency department visit, urgent care visit, home health care services,
primary care physician office visit, pulmonologist office visit, specialist office
visit, other visit, or telehealth contact). Estimates were not included in perprotocol
assessments.
¶ Season 1 vaccine efficacy estimates reflect efficacy against first events
occurring during the first complete RSV season for Northern and Southern
Hemisphere participants (August 2021-October 2022; exact study-defined
season dates were site-dependent).
** Season 2 (interim) vaccine efficacy estimates reflect efficacy against first
events occurring during the second complete RSV season for Northern
Hemisphere participants only (through January 2023; Southern Hemisphere
data not yet available).
†† Interim analysis underpowered to estimate efficacy.
§§ Combined season 1 and 2 (interim) vaccine efficacy estimates reflect efficacy
against first events occurring any time during season 1 or season 2. The mean
time from start to end of efficacy surveillance was approximately 12 months
per participant.
control group participants (pooled RR = 1.43; 95% CI = 0.85-
2.39) (Table 4). The frequency of SAEs across both trials was
similar in the intervention (4.3%) and control (4.1%) groups
(pooled RR = 1.04; 95% CI = 0.94-1.15). A higher number
of participants in the intervention group than in the control
group reported atrial fibrillation as an unsolicited event within
the 30 days after injection (intervention = 10 events [<0.1%];
control = four events [<0.1%], of which seven were SAEs
[intervention = four; control = three]). Among participants
who reported atrial fibrillation, a medical history of atrial
fibrillation was reported by six of 10 Pfizer vaccine recipients
and two of four placebo recipients (26).
Across all Pfizer vaccine clinical trials among older adults,
inflammatory neurologic events were reported in three of
20,255 participants within 42 days after receipt of the vaccine
(15,26,27). The events included GBS in a participant aged
66 years from the United States with symptom onset 14 days
postvaccination; Miller Fisher syndrome (a GBS variant) in
BQ Journal Vol 53 - Q4 2023

Table of Contents for the Digital Edition of BQ Journal Vol 53 - Q4 2023
