Bacterial Infections Clinical Trial
Official title:
Group A Streptococcal Human Challenge Study: Building a Pharyngitis Model to Accelerate Vaccine Development
Group A Streptococcus (GAS) infection is a major cause of death and disability globally with
a disproportionately high burden in settings of disadvantage worldwide. Acute infections due
to GAS range from very common superficial skin infections (>150 million prevalent cases) and
pharyngitis (over 600 million incident cases) to life-threatening invasive disease (>600,000
incident cases) such as necrotising fasciitis. Post-infectious GAS sequelae of GAS include
acute rheumatic fever (ARF, ~500,000 incident cases) leading to rheumatic heart disease (RHD,
~34 million prevalent cases), and acute glomerulonephritis. The health services impact of GAS
disease in all its forms is immense and strikes at every level from primary to intensive
care.
Controlled human infection models (CHIMs) have a long history of critical contributions to
vaccine development. Data from CHIMs meeting modern scientific, regulatory, and ethical
standards, are aiding efforts to control over 25 major human pathogens, including bacteria
(e.g. pneumococcus, cholera), viruses (e.g. respiratory syncytial virus, influenza), and
parasites (e.g. malaria, schistosomiasis).
A reliable and safe controlled human infection model of GAS pharyngitis will be an important
part of the global vaccine development effort. To build the model, the investigators are
undertaking a dose-ranging study using an observational, dose-escalation, inpatient trial to
determine the dose of GAS administered by direct oropharyngeal inoculation (bacteria
'painted' onto throat) required to reliably produce a pharyngitis attack rate of ≥ 60% in
carefully screened healthy adult volunteers.
Group A Streptococcus (GAS) is a ubiquitous human pathogen. Its impact begins in early
childhood and is felt most by those who have the least. Globally, the health services impact
of GAS disease in all its forms is immense and strikes at every level from primary to
intensive care. Despite recognition of the need for GAS vaccine development, there are major
obstacles impeding progress. A human challenge model promises to help to shift inertia in GAS
vaccine development.
The objective of this study is to use an observational, dose-escalation, inpatient trial to
determine the dose of GAS administered by direct oropharyngeal inoculation required to
reliably produce a pharyngitis attack rate of ≥ 60% in carefully screened healthy adult
volunteers. A GAS strain has been specially selected and prepared for this study to ensure
safety and clinical relevance. Potential participants aged 18 to 40 years, the age range
associated with the lowest risk of invasive GAS disease, will be carefully screened to
minimise risk and maximise the likelihood of achieving the pharyngitis endpoint.
The results of three human GAS pharyngeal vaccine-challenge studies from the 1970s are
encouraging, and reassuring. GAS challenge did cause pharyngitis and was safe, with all
participants responding to antibiotics and none experiencing complications, despite these
studies using more aggressive GAS strains.
The study design involves direct oropharyngeal inoculation of GAS to sequential cohorts. Up
to four doses will be tested, from 1-3 x 10^5 cfu/mL (lower than previous GAS challenge
studies) to a maximum of 1-3 x 10^8 cfu/mL. A minimum of 20 and maximum of 80 participants
will be challenged. The challenge procedure aligns closely that used successfully in the
1970s GAS human challenge studies. An incubation period of 36 to 72 hours is expected before
onset of symptoms. Participants will be intensively monitored inpatients for up to six days
after challenge. The primary outcome measure is GAS pharyngitis, as defined by a combination
of positive clinical and laboratory features. All participants developing pharyngitis will be
treated with antibiotics and and those without pharyngitis will also be treated after 5 days.
Participants will be followed as outpatients at 1 week, and 1, 3, and 6 months after
discharge.
*Due to an unexpectedly very high proportion of participants developing pharyngitis at the
starting dose, scope for dose de-escalation was subsequently included in a protocol
amendment, using a dose of 1-3 x 10^4 cfu/mL.
A challenge model also promises an unprecedented opportunity to use modern techniques to
describe the immunobiology of GAS infection. Blood and saliva samples will be collected at
multiple timepoints before, during, and after the challenge. Testing of serial samples will
add a dynamic next level to the clinical foundations of the challenge model, enabling
in-depth comparison between participants developing pharyngitis or not and paving the way to
identifying immune correlates of protection.
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