Access Consortium: Alignment with ICMRA consensus on immunobridging for authorising new COVID-19 vaccines

Placebo-controlled disease endpoint trial data are the gold standard for authorising vaccines. However, for COVID-19 vaccines, it is difficult to conduct efficacy trials in some countries, as few candidates are willing and available to participate. Without established humoral and/or cellular immune parameters that correlate to clinical protection against disease, other approaches are needed to provide sufficient evidence for authorising new COVID-19 vaccines.

The International Coalition of Medicines Regulatory Authorities (ICMRA) convened a workshop on 24 June 2021 to consider the development of COVID-19 vaccines. The ICMRA focused on immunobridging, the design and use of controlled trials (placebo or other controls) and correlates of protection.

Access Consortium members agree that well-justified and appropriately designed immunobridging studies are an acceptable approach for authorising COVID-19 vaccines.

The Consortium provides additional considerations for cross-platform immunobridging. These include extending previous points of consideration for variant-based vaccines that was limited to currently authorised COVID-19 vaccines.

Consensus positions from the ICMRA meeting relevant to this statement include:

• study designs for pivotal trials to demonstrate the efficacy of COVID-19 vaccines must provide robust data for authorisation
• immunogenicity bridging studies can be used if clinical endpoint efficacy studies are no longer feasible
• study designs can be based on either:
  • non-inferiority immunogenicity if the comparator vaccine has demonstrated high efficacy in clinical diseases endpoint efficacy trials and/or
  • superiority if the comparator vaccine has demonstrated modest efficacy
• based on the specifics of the product under consideration, neutralising antibody titre may be justified as immune marker to predict vaccine effectiveness
• neutralising antibody titres should be determined using World Health Organization (WHO)-certified reference standards
• other parameters to be justified include:
  • choice of appropriate vaccine comparators considering the platform
  • statistical criteria
  • population comparator groups (for example, matched by age, gender, prior vaccination/infection status)
• applicant support for sharing information between regulators would help build global convergence.

The Access Consortium considers that the weight of evidence from studies with authorised COVID-19 vaccines is sufficient to support using neutralising antibody titres as a primary endpoint in cross-platform immunobridging trials.

Applicants are to provide a clear rationale regarding the:

• suitability of neutralising antibody as a primary endpoint in immunobridging studies, considering data that support the mechanism of action for the candidate vaccine
• proposed comparator and an appropriate design (for example, comparability margin).

The Consortium also recommends that applicants follow WHO standards in neutralisation assays and consult with the relevant authority early in the study process.

Applicants are also to provide the following.

Non-clinical data

As well as common non-clinical requirements for new vaccines (197kb) and adjuvants (519kb), non-clinical data should include:

• relevant animal challenge studies that support proof of concept for the candidate vaccine and demonstrate effectiveness against variants of concern (VOCs)
• characterisation of comparative immunogenicity profiles, including both antibody- and cell-mediated immunity

Clinical data

Along with a comparison of neutralising antibody titres, clinical data should include:

• characterisation of comparative immunogenicity profiles, including cell-mediated immunity
• characterisation of comparative in vitro neutralisation against VOCs
• safety database of at least 3,000 study participants vaccinated with the dosing regimen intended for authorisation (this is in line with the pre-authorisation safety data requirements for preventive vaccines for infectious diseases)
• commitment for safety and immunogenicity follow-up, for at least 12‑months, of the subjects enrolled in safety/immunobridging trials, which would also record descriptive clinical efficacy data
• commitment for post-authorisation effectiveness studies supported with a study protocol considering current WHO guidance

Applicants are also advised to consult the following:

• Access Consortium: Points to consider for strain changes in authorised COVID-19 vaccines in an ongoing SARS-CoV2 pandemic