Pharmacotherapeutic group: Vaccines, other viral vaccines; ATC code: J07BX05
Mechanism of action
Abrysvo contains two recombinant stabilised RSV prefusion F antigens representing subgroups RSV‑A and RSV‑B. Prefusion F is the primary target of neutralising antibodies that block RSV infection. Following intramuscular administration, the prefusion F antigens elicit an immune response, which protects against RSV‑associated lower respiratory tract disease (LRTD).
In infants born to mothers who were vaccinated with Abrysvo between weeks 24 and 36 of gestation, protection against RSV-associated LRTD is due to transplacental transfer of RSV neutralising antibodies. Adults 18 years of age and older are protected by active immunisation.
Clinical efficacy
Infants from birth through 6 months of age by active immunisation of pregnant individuals
Study 1 was a phase 3, multicentre, randomised (1:1), double-blind, placebo‑controlled study to assess the efficacy of a single dose of Abrysvo in the prevention of RSV‑associated LRTD in infants born to pregnant individuals vaccinated between weeks 24 and 36 of gestation. The need for revaccination with subsequent pregnancies has not been established.
RSV-associated LRTD was defined as a medically attended visit in individuals with a reverse transcription-polymerase chain reaction (RT-PCR) confirmation of RSV and with one or more of the following respiratory symptoms: fast breathing, low oxygen saturation (SpO2 <95%) and chest wall indrawing. Severe RSV-associated LRTD was defined as RSV‑associated LRTD that additionally met at least one of the following criteria: very fast breathing, low oxygen saturation (SpO2 <93%), high-flow oxygen supplementation via nasal cannula or mechanical ventilation, ICU admission for >4 hours and/or failure to respond/unconscious.
In this study, 3 711 pregnant individuals with uncomplicated, singleton pregnancies were randomised to the Abrysvo group and 3 709 to placebo.
Vaccine efficacy (VE) was defined as the relative risk reduction of the endpoint in the Abrysvo group compared to the placebo group for infants born to pregnant individuals who received the assigned intervention. At the primary analysis, there were two primary efficacy endpoints, assessed in parallel, severe RSV‑positive medically attended LRTD and RSV‑positive medically attended LRTD, occurring within 90, 120, 150 or 180 days after birth.
Of the pregnant women who received Abrysvo, 65% were White, 20% were Black or African American and 29% were Hispanic/Latino. The median age was 29 years (range 16‑45 years); 0.2% of participants were under 18 years of age and 4.3% were under 20 years of age. The median gestational age at vaccination was 31 weeks and 2 days (range 24 weeks and 0 days to 36 weeks and 4 days). The median infant gestational age at birth was 39 weeks and 1 day (range 27 weeks and 3 days to 43 weeks and 6 days).
Vaccine efficacy is presented in Tables 2, 3, 4 and 5.
Table 2 Vaccine efficacy of Abrysvo against severe medically attended LRTD caused by RSV in infants from birth through 6 months of age by active immunisation of pregnant individuals – Study 1
| Time period | Abrysvo Number of cases N=3 495 | Placebo Number of cases N=3 480 | VE % (CI)a |
| 90 days | 6 | 33 | 81.8 (40.6, 96.3) |
| 120 days | 12 | 46 | 73.9 (45.6, 88.8) |
| 150 days | 16 | 55 | 70.9 (44.5, 85.9) |
| 180 days | 19 | 62 | 69.4 (44.3, 84.1) |
CI = confidence interval; VE = vaccine efficacy
a 99.5% CI at 90 days; 97.58% CI at later intervals
Table 3 Vaccine efficacy of Abrysvo against medically attended LRTD caused by RSV in infants from birth through 6 months of age by active immunisation of pregnant individuals – Study 1
| Time period | Abrysvo Number of cases N=3 495 | Placebo Number of cases N=3 480 | VE % (CI)a |
| 90 days | 24 | 56 | 57.1 (14.7, 79.8) |
| 120 days | 35 | 81 | 56.8 (31.2, 73.5) |
| 150 days | 47 | 99 | 52.5 (28.7, 68.9) |
| 180 days | 57 | 117 | 51.3 (29.4, 66.8) |
CI = confidence interval; VE = vaccine efficacy
a 99.5% CI at 90 days; 97.58% CI at later intervals
Table 4 Vaccine efficacy of Abrysvo against severe medically attended LRTD caused by RSV in infants from birth through 6 months of age by active immunisation of pregnant individuals between weeks 28 and 36 of gestation – Study 1a
| Time period | Abrysvo Number of cases N=2 602 | Placebo Number of cases N=2 609 | VE % (CI)b |
| 90 days | 2 | 22 | 90.9 (62.9, 99.0) |
| 120 days | 5 | 31 | 83.8 (58.0, 95.1) |
| 150 days | 6 | 38 | 84.2 (62.3, 94.5) |
| 180 days | 8 | 43 | 81.3 (59.9, 92.4) |
CI = confidence interval; VE = vaccine efficacy
a This post-hoc descriptive subgroup analysis was not controlled for multiple comparisons
b 95% CI
Table 5 Vaccine efficacy of Abrysvo against medically attended LRTD caused by RSV in infants from birth through 6 months of age by active immunisation of pregnant individuals between weeks 28 and 36 of gestation – Study 1a
| Time period | Abrysvo Number of cases N=2 602 | Placebo Number of cases N=2 609 | VE % (CI)b |
| 90 days | 18 | 43 | 58.0 (25.7, 77.2) |
| 120 days | 25 | 61 | 58.9 (33.6, 75.3) |
| 150 days | 30 | 76 | 60.4 (38.9, 75.0) |
| 180 days | 35 | 90 | 61.0 (41.8, 74.4) |
CI = confidence interval; VE = vaccine efficacy
a This post-hoc descriptive subgroup analysis was not controlled for multiple comparisons
b 95% CI
Individuals 60 years of age and older
Study 2 was a phase 3, multicentre, randomised, double‑blind, placebo-controlled study to assess the efficacy of Abrysvo in the prevention of RSV‑associated LRTD in individuals 60 years of age and older.
RSV-associated LRTD was defined as RT‑PCR confirmed RSV disease with two or more or three or more of the following respiratory symptoms within 7 days of symptom onset and lasting more than 1 day during the same illness: new or increased cough, wheezing, sputum production, shortness of breath or tachypnoea (≥25 breaths/min or 15% increase from resting baseline).
Participants were randomised (1:1) to receive Abrysvo (n=18 487) or placebo (n=18 479). Enrollment was stratified by age 60-69 years (63%), 70-79 years (32%) and ≥80 years (5%). Subjects with stable chronic underlying conditions were eligible for this study and 52% of participants had at least 1 prespecified condition; 16% of participants were enrolled with stable chronic cardiopulmonary conditions such as asthma (9%), chronic obstructive pulmonary disease (7%) or congestive heart failure (2%). Immunocompromised individuals were ineligible.
The primary objective was assessment of vaccine efficacy (VE), defined as the relative risk reduction of first episode of RSV-associated LRTD in the Abrysvo group compared to the placebo group in the first RSV season.
Of the participants who received Abrysvo, 51% were male and 80% were White, 12% were Black or African American and 42% were Hispanic/Latino. The median age of participants was 67 years (range 59‑95 years).
At the end of the first RSV season the analysis demonstrated statistically significant efficacy for Abrysvo for reduction of RSV-associated LRTD with ≥2 symptoms and with ≥3 symptoms.
Vaccine efficacy information at the end of the first RSV season (median follow‑up time 7.4 months) is presented in Table 6.
Table 6 Vaccine efficacy of Abrysvo against RSV disease - active immunisation of individuals 60 years of age and older – Study 2
| Efficacy endpoint | | Abrysvo | Placebo | VE (%) (95% CI) |
| | | N | n | N | n | |
| First episode of RSV-associated LRTD with ≥2 symptomsa | Overall | 18 058 | 15 | 18 076 | 43 | 65.1 (35.9, 82.0) |
| Age 60-69 years | 11 305 | 10 | 11 351 | 25 | 60.0 (13.8, 82.9) |
| Age 70-79 years | 5 750 | 4 | 5 742 | 12 | 66.7 (-10.0, 92.2) |
| With ≥1 significant underlying condition | 9 377 | 8 | 9 432 | 22 | 63.6 (15.2, 86.0) |
| First episode of RSV-associated LRTD with ≥3 symptomsb | Overall | 18 058 | 2 | 18 076 | 18 | 88.9 (53.6, 98.7) |
| Age 60-69 years | 11 305 | 2 | 11 351 | 11 | 81.8 (16.7, 98.0) |
| Age 70-79 years | 5 750 | 0 | 5 742 | 4 | 100 (-51.5, 100.0) |
| With ≥1 significant underlying condition | 9 377 | 2 | 9 432 | 11 | 81.8 (16.7, 98.0) |
CI – confidence interval; RSV – respiratory syncytial virus; VE – vaccine efficacy
N = number of participants; n = number of cases
a In an exploratory analysis in RSV subgroup A (Abrysvo n=3, placebo n=16) VE was 81.3% (CI 34.5, 96.5); and in RSV subgroup B (Abrysvo n=12, placebo n=26) VE was 53.8% (CI 5.2, 78.8).
b In an exploratory analysis in RSV subgroup A (Abrysvo n=1, placebo n=5) VE was 80.0% (CI -78.7, 99.6); and in RSV subgroup B (Abrysvo n=1, placebo n=12) VE was 91.7% (CI 43.7, 99.8).
Vaccine efficacy in the subgroup of participants 80 years of age and older (995 and 981 participants in the Abrysvo and placebo groups, respectively) cannot be concluded due to the low number of total cases accrued (7 cases of RSV-associated LRTD with ≥2 symptoms and 3 cases of RSV-associated LRTD with ≥3 symptoms).
Efficacy against RSV-associated lower respiratory tract disease over 2 RSV seasons in individuals 60 years of age and older
Across 2 RSV seasons with median follow-up time of 16.4 months, VE against RSV‑associated LRTD with ≥2 symptoms was 58.8% (95% CI 43.0, 70.6; 54 cases in the Abrysvo group and 131 cases in the placebo group) and with ≥3 symptoms was 81.5% (95% CI 63.3, 91.6; 10 cases in the Abrysvo group and 54 cases in the placebo group). VE against RSV‑associated LRTD caused by RSV-A and RSV-B was 66.3% (95% CI 47.2, 79.0) and 50.0% (95% CI 18.5, 70.0) for cases with ≥2 LRTD symptoms respectively, and 80.6% (95% CI 52.9, 93.4) and 86.4% (95% CI 54.6, 97.4) for cases with ≥3 LRTD symptoms, respectively.
Across 2 RSV seasons, subgroup analyses of VE by age and significant underlying conditions were consistent with VE at the end of the first RSV season and support consistent VE across different age and risk groups.
Immunogenicity in individuals 18 through 59 years of age considered to be at increased risk of LRTD caused by RSV.
Study 3 was a Phase 3, multicentre, randomised, double-blind, placebo-controlled study to assess the safety and immunogenicity of Abrysvo in individuals 18 through 59 years of age considered to be at high risk of developing severe LRTD caused by RSV. Study 3 enrolled individuals who had chronic pulmonary (including asthma), cardiovascular (excluding isolated hypertension), renal, hepatic, neurologic, haematologic or metabolic disorders (including diabetes mellitus and hyper/hypothyroidism). Participants were randomised (2:1) to receive a single dose of Abrysvo (n=437) or placebo (n=217).
Demographic characteristics in study 3 were generally similar with regard to age, race and ethnicity among participants who received Abrysvo and those who received placebo. Fifty-three percent (53%) were 18 to 49 years and 47% were 50 to 59 years. The vaccine and placebo groups were similar with regards to having at least one prespecified medical condition, which included 53% with ≥1 chronic pulmonary condition, 8% with ≥1 cardiovascular condition, 42% with diabetes and 31% ≥1 other disease (liver, renal, neurologic, haematologic or other metabolic disease).
Vaccine efficacy in individuals 18 through 59 years of age is inferred by immunobridging to study 2 where vaccine efficacy was demonstrated in individuals 60 years of age and older. The non‑inferiority criteria were met for high risk individuals 18 through 59 years of age compared to a randomly selected immunogenicity subset (external control group) of individuals ≥60 years of age from study 2 for the ratio of RSV neutralising geometric mean titres (GMTs) by the lower bounds of the 2‑sided 95% CIs >0.667 (1.5‑fold non‑inferiority margin), and for the difference in seroresponse rates by the lower bounds of the 2‑sided 95% CIs > -10% for both RSV A and RSV B.
Table 7 Comparison of model adjusted RSV neutralising titre GMTs at 1 month after vaccination with Abrysvo, 18 through 59 years at high risk (Study 3) versus 60 years and older (Study 2)
| | Study 3 18-59 years of age at high risk | Study 2 ≥60 years | ANCOVA comparison |
| RSV subgroups | n | Adjusted GMT (95% CI) | n | Adjusted GMT (95% CI) | Adjusted GMR (95% CI) |
| A | 435 | 41097 (37986, 44463) | 408 | 26225 (24143, 28486) | 1.57 (1.396, 1.759) |
| B | 437 | 37416 (34278, 40842) | 408 | 24680 (22504, 27065) | 1.52 (1.333, 1.725) |
CI – confidence interval; GMR – geometric mean ratio; GMT – geometric mean titre
Table 8 Comparison of RSV neutralising titre seroresponse rates 1 month after vaccination with Abrysvo, 18 through 59 years at high risk (Study 3) versus 60 years and older (Study 2)
| | Study 3 18-59 years of age at high risk | Study 2 ≥60 years | Comparison |
| RSV subgroups | n/N (%) | 95% CI | n/N (%) | 95% CI | Difference (95% CI) |
| A | 405/435 (93) | 90.3, 95.3 | 359/408 (88) | 84.4, 91.0 | 5.1 (1.2, 9.2) |
| B | 408/437 (93) | 90.6, 95.5 | 347/408 (85) | 81.2, 88.4 | 8.3 (4.2, 12.6) |
CI – confidence interval
Immunogenicity in immunocompromised individuals 18 years of age and older
Study 4 (C3671023 Substudy B) was a Phase 3, single-arm, open-label, multicentre study to assess the safety and immunogenicity of Abrysvo in immunocompromised individuals ≥18 years of age. Participants had history of a solid organ transplant (kidney, liver, lung or heart) at least 3 months prior to enrollment; end stage renal disease and on haemodialysis; autoimmune inflammatory disorders with active immunomodulator therapy; or advanced non-small cell lung cancer and receiving active immunomodulator therapy. Participants received 2 doses of Abrysvo with an interval of 1 month.
A single dose of Abrysvo was sufficient to elicit robust neutralising responses approximately 8- or 9- fold above baseline against RSV A and RSV B in participants ≥18 years of age with immunocompromising conditions (n=188). Responses did not further increase with a second dose of Abrysvo 1 month after the first dose.
Paediatric population
The licensing authority has deferred the obligation to submit the results of studies with Abrysvo in children from 2 to less than 18 years of age in prevention of lower respiratory tract disease caused by RSV (see section 4.2 for information on paediatric use).