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GSK starts phase 3 study of RSV maternal candidate vaccine

  • Currently no vaccine is available for respiratory syncytial virus (RSV)
  • RSV-associated lower respiratory tract illnesses (LRTIs) cause significant global morbidity and mortality in infants under 6 months, including more than 1.4 million hospitalisations every year
  • The GRACE study evaluates the safety of the candidate vaccine for pregnant mothers and infants, and its efficacy in infants born to vaccinated mothers
  • Phase 1/2 trial demonstrated strong immunogenicity of vaccine candidate

GlaxoSmithKline plc (LSE/NYSE: GSK) today announced that patient dosing has begun in a phase 3 clinical programme investigating the safety and efficacy of its Respiratory Syncytial Virus (RSV) candidate vaccine for maternal immunisation (GSK3888550A), following  presentation of positive phase 1/2 safety, reactogenicity and immunogenicity data last month

It is estimated that every year, 33 million cases of RSV occur in children less than 5 years of age globally, with more than 1.4 million hospitalisations of infants under 6 months of age[1]. RSV is a leading cause of respiratory infections such as bronchiolitis (inflammation and congestion of the small airways or bronchioles of the lung) and viral pneumonia (an inflammatory condition of the lung small air sacs or alveoli) in infants.

Emmanuel Hanon, Senior Vice President and Head of Vaccines R&D for GSK, said: “RSV burden is high amongst young infants – a vaccine which protects them from birth would represent significant progress in addressing the burden of RSV, preventing infant illness and families’ distress, as well as reducing the associated burden for society. Advancing our portfolio of RSV vaccine candidates based on robust available data is a major step towards GSK’s goal of reducing the RSV-associated disease burden around the world.”

The candidate vaccine contains a recombinant subunit pre-fusion RSV antigen (RSVPreF3) which has shown promising safety and immunogenicity in a phase 1/2 study in non-pregnant women, as presented at the ID Week Congress in October 2020. The data showed the candidate vaccine was well-tolerated and able to rapidly boost the pre-existing immunity in non-pregnant women leading to a high level of protecting neutralising antibodies, with a 14-fold increase in RSV-A and RSV-B neutralising antibody titers observed as early as one week after immunisation. First data in pregnant women are expected to be presented in 2021.

This candidate vaccine is part of a portfolio of RSV vaccine candidates that GSK is developing, which also includes candidates for infants and older adults. The candidate vaccines are based on different novel technologies, tailored to the needs of the populations most impacted. All three candidate vaccines have received FDA fast-track designation. The phase 3 programme for the older adult’s RSV candidate vaccine is on-track to start in the coming months, while the phase 1/2 (in RSV sero-naive infants) study with the paediatric RSV candidate vaccine is ongoing.

About the GRACE Study

The investiGational RSV mAternal vacCinE study (GRACE) is a double-blind phase 3 study (NCT04605159) to be conducted in up to 10,000 pregnant women aged 18-49 years[2]. The trial evaluates the efficacy of a single dose of the RSV Maternal unadjuvanted candidate vaccine administered intramuscularly to pregnant women in good general maternal health aged 18-49 years for the prevention of medically assessed RSV-associated LRTIs in their new-born infants. The study also evaluates the safety of the candidate vaccine both in vaccinated mothers and in their infants.

The study is estimated to end in early 2024, with interim results expected by the second half of 2022.

About GSK’s maternal RSV candidate vaccine (GSK3888550A)

The goal of this candidate vaccine is to prevent medically assessed RSV-associated LRTIs in infants during the first 6 months of life by transfer of maternal antibodies – an approach based on GSK’s strong expertise in maternal immunisation. The polyclonal nature of the humoral response boosted by this vaccine may offer broad protection and address the potential issue of development of virus escape mutants. If successful, infants would be born with protection due to the passive transfer of neutralising antibodies from the vaccinated mother to the unborn child in the last weeks of pregnancy and therefore no medical intervention in the newborn is required. Maternal immunisation could help to protect infants that are too young to be immunised in their first months of life – when they are most vulnerable to RSV infections.

Data from a phase 1/2 study (NCT03674177) based on 502 healthy non-pregnant women were presented at ID Week Congress in October 2020. They showed that the candidate vaccine was well-tolerated, with no safety concerns identified: the most frequently reported solicited adverse events were minor and included pain at injection site and headache. Moreover, the data showed that the candidate vaccine elicited a rapid and persistent immune response in all RSVPreF3 groups studied. The immune response peaked at Day 8 with a 14-fold increase in neutralising RSV-A and RSV-B titers from baseline. The neutralising titers declined over time but a >6-fold increase was still maintained at Day 91. Anti-RSVPreF3 IgG antibodies were boosted substantially with geometric mean concentrations of anti-RSVPreF3 IgG antibody (≥ 12-fold at Day 8 and ≥ 6-fold until Day 91 vs baseline).

Safety and immunogenicity data of the RSV Maternal vaccine candidate from the first clinical study with pregnant women will be presented in the first half of 2021.

About respiratory syncytial virus

Globally, there are an estimated 33 million cases of RSV annually in children less than 5 years of age, with about 3 million hospitalised and approximately 120,000 dying each year from complications associated with the infection. Nearly half of these paediatric hospitalisations and deaths occur in infants less than 6 months of age[3]. According to the Centers for Disease Control and Prevention, virtually all children in the US get an RSV infection by the time they are 2 years old and one to two out of every 100 children younger than 6 months of age with RSV infection may need to be hospitalised[4].

It also represents a significant health threat for older adults, with an estimated 177,000 hospitalisations and 14,000 deaths associated with RSV infections occurring in the US alone[5]. Without robust surveillance systems in several countries, global data on the burden of RSV in older adults is either lacking or likely to underestimate its significance. As global population ages, morbidity and mortality of respiratory infections including RSV to be steadily increasing.

About GSK

GSK is a science-led global healthcare company with a special purpose: to help people do more, feel better, live longer. For further information please visit


[1] Shi T. et al, Lancet. 2017; 390:946–58

[2] Since the analysis will be case-driven, incidence rates and vaccine efficacy estimates will drive the actual sample size.

[3] Shi T. et al, Lancet. 2017;390:946–58

[4] CDC -   

[5] CDC -