NEW HAVEN, Conn., October 14, 2026

Invivyd, Inc. (Nasdaq: IVVD) and the SPEAR Study Group announced the initiation of FLINTLOCK, a Phase 2 clinical trial evaluating investigational monoclonal antibody VYD2311 in adults with Long COVID or Post-Vaccination Syndrome (PVS). The randomized, double-blind, placebo-controlled study will assess the candidate’s safety, tolerability, pharmacokinetics and potential clinical efficacy over 90 days. Approximately 130 participants aged 18–65 years are expected to enroll. The study is designed to investigate whether sustained antibody exposure against the SARS-CoV-2 spike protein could provide a potential treatment approach for people experiencing persistent symptoms following COVID-19 infection or vaccination. Initial data are expected in mid-2027. The trial forms part of Invivyd’s broader REVOLUTION clinical development program for VYD2311, which also includes the DECLARATION and LIBERTY studies..

FLINTLOCK Evaluates Three-Dose Treatment Regimen

The FLINTLOCK study will investigate VYD2311 using an initial high-dose intravenous infusion on Day 1, followed by intramuscular injections on Days 30 and 60. The total dose is targeted at approximately 10 times the prophylactic dose evaluated in the DECLARATION and LIBERTY studies, while remaining below doses previously assessed with an initially positive safety profile in first-in-human testing, according to the company. Participants will be randomized to receive VYD2311 or placebo, allowing investigators to compare safety outcomes and potential clinical effects. Eligibility criteria are designed to include adults with a confirmed diagnosis of Long COVID or PVS who have at least two persistent symptoms present for six months or longer following COVID-19 infection or vaccination. The study will assess clinical activity through Day 90 using functional performance tests consistent with those used in research on Long COVID and other infection-associated chronic conditions. Investigators will also monitor treatment-emergent adverse events, hypersensitivity reactions and serum concentrations of VYD2311 to characterize its pharmacokinetic profile. The trial is intended as a proof-of-concept study, and its findings will be needed to determine whether the treatment approach warrants further clinical development.

VYD2311 Targets SARS-CoV-2 Spike Protein

VYD2311 is an investigational monoclonal antibody developed using Invivyd’s proprietary integrated technology platform. The candidate was engineered through serial molecular evolution to optimize neutralization of SARS-CoV-2 lineages. The company reports that VYD2311 has demonstrated high in vitro antiviral potency against all SARS-CoV-2 variants tested, spanning the original Wuhan strain through contemporary Omicron variants. Its pharmacokinetic profile and neutralizing activity are being investigated for their potential to support therapeutic and prophylactic applications. VYD2311 shares an antibody backbone with pemivibart, marketed under the name PEMGARDA in the company’s announcement, which has received U.S. emergency use authorization for pre-exposure prophylaxis in certain immunocompromised individuals. However, PEMGARDA is not authorized for treating Long COVID or Post-Vaccination Syndrome, and its authorization for a different use does not establish that VYD2311 is effective for these conditions. Invivyd Chairman and Chief Executive Officer Marc Elia said the company is investigating whether its spike-protein-directed antibody approach could address a potential component of persistent disease processes. The proposed relationship between persistent spike protein and symptoms remains an area requiring further scientific and clinical evaluation; the FLINTLOCK trial is intended to generate evidence about VYD2311’s safety and potential clinical activity.

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REVOLUTION Program Expands Clinical Investigation

FLINTLOCK adds a potential treatment-focused study to Invivyd’s broader VYD2311 development program. The Phase 3 DECLARATION study evaluates the candidate for prevention of symptomatic COVID-19, while LIBERTY has evaluated its safety, pharmacokinetics and neutralizing antibody responses in a study involving an mRNA COVID-19 vaccine, including co-administration. These studies address different research questions from FLINTLOCK, which focuses on adults with persistent symptoms attributed to Long COVID or PVS. The SPEAR Study Group, whose name stands for Spike Protein Elimination and Recovery, was formed by Invivyd and researchers to assess monoclonal antibody therapy in these populations. David Putrino, PhD, Nash Family Director of the Cohen Center for Recovery from Complex Chronic Illness at Mount Sinai and a founding member of the group, highlighted the ongoing burden of persistent multisystem symptoms and the need for further research. Long COVID can involve a range of symptoms affecting daily functioning, while PVS is being studied separately in the trial’s eligibility framework. The mid-2027 initial data readout is expected to provide early evidence on VYD2311’s tolerability, pharmacokinetics and potential clinical effects. Until those results are available, the candidate’s effectiveness for either condition remains unestablished.

Source::Invivyd press release