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For life and breath.

Live Attenuated Vaccines for Life-Threatening Respiratory Viruses

Respiratory viruses are one of the biggest threats to human health. Vaccines are the most effective healthcare tool to combat infectious diseases and have saved more lives than any other type of medicine. Meissa is dedicated to creating safe, potent, stable, and accessible intranasal live attenuated vaccines that can prevent infection and disease. Meissa’s RSV and COVID-19 live attenuated vaccine candidates were developed using the company’s AttenuBlock platform.

Meissa’s Vaccine Pipeline

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Meissa’s pipeline of live attenuated vaccine candidates are being developed to protect against respiratory syncytial virus, SARS-CoV-2, human metapneumovirus, and parainfluenza virus.

Our Intranasal Vaccines Induce Both Mucosal and Circulating Antibodies

Intranasal vaccines generate both mucosal (IgA) antibodies in the nasal cavity and antibodies that circulate in the blood (serum). In contrast, injected vaccines typically induce circulating but not mucosal antibodies. While circulating antibodies are important for preventing serious lung disease, mucosal antibodies are important for blocking infection and viral transmission. The potential to prevent viral transmission is a key advantage that intranasal vaccines have due to the mucosal immune response that is induced.


In a Phase 1 clinical trial, Meissa’s RSV vaccine candidate stimulated a strong mucosal IgA response in adults who already had circulating antibodies to RSV in their blood. These results were consistent with previous animal studies, in which Meissa’s RSV vaccine candidate stimulated strong mucosal IgA antibody and circulating antibody responses and prevented infection of both the upper and lower respiratory tracts. Collectively, these results warrant further development of our vaccine candidates by demonstrating both mucosal and systemic immunity that blocks infection and prevents disease. 

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Meissa's RSV Live Attenuated Vaccine Candidate

Meissa is developing MV-012-968, an intranasal (needle-free), adjuvant-free, live attenuated vaccine candidate, to protect infants and at-risk, older adults from RSV. In Phase 1 clinical trials, Meissa’s RSV vaccine candidate was well-tolerated, heavily attenuated, and stimulated a strong RSV-specific mucosal IgA response in participants (adults and young children), who had previously been infected and already had circulating antibodies to RSV in their blood ( identifiers NCT04444284 and NCT04227210). These results differentiate Meissa’s RSV vaccine from other live attenuated RSV vaccine candidates and are consistent with previous animal studies, in which Meissa’s RSV vaccine candidate was highly attenuated yet led to robust immune responses and protected both the upper and lower respiratory tracts from RSV challenge. MV-012-968 is currently being tested in a Phase 2a, randomized, double-blind, placebo-controlled challenge study, designed to evaluate the safety and prophylactic efficacy of the Meissa vaccine against symptomatic RSV infection ( identifier: NCT04690335).


About RSV 


Respiratory syncytial virus (RSV) is the leading cause of infant hospitalization in the United States and is considered a “missing” mandatory pediatric vaccine. RSV is also a significant cause of morbidity and mortality in older adults. In the United States, approximately 1% of infants are hospitalized by RSV each year. Globally, RSV causes more than 118,000 deaths per year and over 3 million hospitalizations in children less than five years of age (Anderson 2013).

Meissa’s COVID-19 Live Attenuated Vaccine Candidate

Meissa is developing a live attenuated COVID-19 vaccine candidate, MV-014-212, to induce mucosal and systemic immunity and protect against SARS-CoV-2, the novel coronavirus that causes COVID-19. Like Meissa’s RSV vaccine candidate, MV-014-212 offers significant potential advantages for global deployment, including needle-free intranasal administration, a single adjuvant-free dose to induce mucosal and systemic immunity, as well as a straightforward, economical, and scalable manufacturing process. A Phase 1 clinical study has been initiated in the U.S. to evaluate the safety, tolerability, and immunogenicity of a single intranasal dose of MV-014-212 ( identifier: NCT04798001). 


Preclinical data in nonhuman primates (NHPs) of MV-014-212 demonstrate that a single adjuvant-free dose of MV-014-212 provided equivalent protection against SARS-CoV-2 challenge compared to reported efficacy in NHP models of currently authorized vaccines. Furthermore, the data show that MV-014-212 stimulates mucosal (nasal IgA) antibodies in the upper respiratory tract, the major infection route for SARS-CoV-2, and systemic (serum neutralizing and binding IgG) antibodies. The mucosal immune response is the first line of defense against respiratory viruses, providing fast-acting protection at the primary site of exposure. In NHPs, Meissa’s intranasal COVID-19 vaccine generated both mucosal and systemic antibodies and was highly protective against wild-type SARS-CoV-2 challenge. Serum antibodies were able to neutralize wild-type SARS-CoV-2, B.1.351 (Beta, South Africa), and B.1.1.7 (Alpha, UK). Additional data from serial passaging in manufacturing cell line and virus shed from NHPs showed that MV-014-212 has a stable genotype in vitro and in vivo (download the manuscript and supplemental material).

SARS-CoV-2 Variants

Vaccines against SARS-CoV-2 and emerging variants will be needed on an ongoing basis so long as SARS-CoV-2 circulates. Meissa’s MV-014-212 stimulates cross-neutralizing serum antibodies against SARS-CoV-2 variants of concern. Furthermore, our AttenuBlock platform is amenable to generation of vaccine constructs to combat future variants as needed.

To stay informed about our clinical progress for our our RSV and COVID-19 vaccine candidates, sign up for our e-updates.

Meissa Vaccines Expanded Access Policy (rev. August 2021)

Meissa Vaccines is developing investigational vaccines for the prevention of respiratory diseases.  Since the vaccines are designed for prophylactic not treatment use, Meissa has chosen not to offer Expanded Access to these vaccines and will not accept Expanded Access requests. Meissa’s investigational vaccines will only be provided through ongoing clinical trials. To learn more about available clinical trials, please see above or visit and search using the company name.