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Pfizer's Abrysvo approved in US to prevent RSV infection in infants |iPharmaCenter

The Food and Drug Administration (FDA) approved Abrysvo, Pfizer's vaccine designed to prevent Respiratory Syncytial Virus (RSV) in infants through the active immunization of pregnant individuals between 32 and 36 weeks of gestational age. This marks a significant milestone as the first maternal vaccine approved in the U.S. to safeguard infants from birth to six months against lower respiratory tract disease (LRTD) and severe LRTD caused by RSV.


The FDA's decision stems from comprehensive data collected during a pivotal Phase 3 clinical trial involving over 7,000 pregnant individuals and more than 14,000 participants, including their infants. Pfizer announced that its bivalent RSV prefusion F (RSVpreF) vaccine, Abrysvo, has been granted FDA approval for preventing both LRTD and severe LRTD attributable to RSV in infants from birth to six months. The vaccine achieves this by actively immunizing pregnant individuals during the 32nd to 36th weeks of gestation. Abrysvo comprises two preF proteins selected to provide optimal protection against RSV A and B strains. Notably, it is unadjuvanted and has demonstrated both safety and effectiveness.



The FDA's decision finds its basis in data sourced from the pivotal Phase 3 clinical trial known as MATISSE (MATernal Immunization Study for Safety and Efficacy), registered as NCT04424316. This trial, designed as a randomized, double-blind, placebo-controlled Phase 3 study, aimed to assess the vaccine's efficacy, safety, and immunogenicity against LRTD and severe LRTD caused by RSV in infants born to healthy pregnant individuals who received the vaccine.


The study involved 3,682 maternal participants who received the vaccine, while 3,676 received a placebo. Among these participants were 3,570 infants evaluated in the vaccine group and 3,558 infants in the placebo group.

During the 90 days following birth, six infants born to mothers in the vaccine group experienced medically attended severe lower respiratory tract illness. In contrast, 33 infants born to mothers in the placebo group faced the same condition during the same timeframe. This resulted in a calculated vaccine efficacy of 81.8%, indicating a robust protective effect.

Looking at a longer window, within 180 days after birth, 19 cases of medically attended severe lower respiratory tract illness among infants in the vaccine group, whereas 62 cases were reported among infants in the placebo group. This yielded a vaccine efficacy of 69.4%. These findings underscore the substantial effectiveness of the vaccine in reducing the incidence of severe lower respiratory tract illness in infants born to vaccinated mothers, particularly during the first six months of life.


RSV is a contagious virus with global prevalence, frequently causing respiratory illnesses. It targets the lungs and airways, potentially leading to severe consequences or death. RSV infections are widespread among young children, with nearly all children experiencing an RSV infection by age two. In the United States alone, RSV leads to 500,000 to 600,000 cases of LRTD in infants annually, emerging as a significant cause of hospitalization in children below one year of age.


Pfizer currently holds the distinction of being the only company offering protection against RSV for both older adults and infants through maternal immunization. In May 2023, the FDA approved RSVpreF, now known as Abrysvo, to combat LRTD caused by RSV in individuals aged 60 and above. Subsequently, in June, the Advisory Committee on Immunization Practices (ACIP) from the U.S. CDC formally endorsed the utilization of the vaccine for individuals aged 60 and above.


In July 2023, Pfizer announced that the Committee for Medicinal Products for Human Use (CHMP) in Europe had provided a favourable opinion for authorising the RSV vaccine candidate, PF-06928316 or RSVpreF. This candidate aims to safeguard older adults and infants through maternal immunization, specifically targeting protection against RSV. This recommendation is under review by the European Commission (EC), which will ultimately determine whether to approve RSVpreF to be named Abrysvo within the European Union (EU).


Pfizer's commitment to RSV prevention extends globally. In February 2023, Pfizer Japan initiated an application with the MHLW for RSVPreF as a maternal immunization to safeguard infants against RSV. Similarly, Pfizer Canada announced in April 2023 that Health Canada had accepted RSVpreF for review, considering its potential to protect individuals aged 60 and older and its role as a maternal immunization strategy for infant protection against RSV.


Looking forward, Pfizer has launched two additional clinical trials focusing on Abrysvo. One trial concentrates on children aged 2 to under 18 who are at a higher risk of RSV disease, while the other trial assesses adults aged 18 to 60, particularly those with underlying medical conditions like asthma, diabetes, COPD, and immunocompromised adults aged 18 and above, who face an elevated risk of RSV. The company also intends to conduct post-marketing studies and surveillance programs to understand the vaccine's safety profile further.

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