A recent report published in the New England Journal of Medicine has revealed that the coronavirus disease 2019 (COVID-19) vaccine developed by Moderna, Inc, USA, is capable of inducing robust and durable antibody responses for at least six months post-vaccination.
As of April 7, 2021, globally, there have 132 million cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, including 2.8 million deaths, registered to the World Health Organization (WHO). Although the infection and mortality rates remained intensively high throughout the initial phase of the COVID-19 pandemic, the global population is currently heading towards achieving herd immunity because of the mass vaccination programs. According to the WHO report, so far, a total of 604 million doses of COVID-19 vaccines have been administered worldwide.
Among various vaccines that are currently rolling out in many countries, mRNA-based COVID-19 vaccines have shown more than 90% efficacy in preventing SARS-CoV-2 infection and reducing disease severity.
In the current report, the scientists have demonstrated the long-term efficacy of the mRNA-1273 COVID-19 vaccine, which was developed by a US-based biotechnology company Moderna, Inc., in association with the National Institute of Allergy and Infectious Diseases (NIAID). This report is a part of the National Institutes of Health (NIH)-led phase 1 study of the mRNA-1273 vaccine.
What is known about mRNA-1273 COVID-19 vaccine?
The mRNA-1273 vaccine is a lipid nanoparticle-encapsulated mRNA-based vaccine that contains prefusion stabilized full-length spike protein of SARS-CoV-2 as an immunogen. Regarding the immunization regimen, two doses of the vaccine (100 µg each) are administered intramuscularly at an interval of 28 days.
The phase III randomized, placebo-controlled clinical trial conducted at various centers across the USA has revealed that the vaccine is 94% effective in preventing symptomatic COVID-19 in high-risk individuals. Moreover, apart from local and systemic reactions, no severe adversities have been observed in immunized individuals.
The vaccine has received emergency use authorization from the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) and is currently rolling out in many countries.
Although largely safe, the vaccine is not recommended for individuals with a known history of severe allergic reaction to any component of the vaccine. Moreover, individuals under the age of 18 years should not be immunized with the mRNA-1273 vaccine.
Not enough data is currently available to demonstrate the safety and efficacy profiles of the vaccine in pregnant and breastfeeding women.
Current study design
The long-term efficacy of the mRNA-1273 vaccine was investigated in 33 healthy adult participants who received the second vaccine dose six months before the commencement of the study.
By conducting enzyme-linked immunosorbent assay (ELISA) against the spike receptor-binding domain (RBD), the scientists estimated that the average titers of binding antibodies in participants aged 18 – 55 years, 56 – 70 years, and above 70 years were around 92,000, 62,000, and 49,000, respectively.
Moreover, by conducting a pseudovirus neutralization assay and live-virus focus-reduction neutralization assay, they observed that nearly all participants exhibited detectable virus neutralization activity.
Using two approaches, they calculated the half-life of both binding and neutralizing antibodies against SARS-CoV-2. The findings revealed that the antibody decay rates reduce over time. Overall, the findings are in line with previous observations demonstrating that most COVID-19 recovered patients remain protected from reinfection for at least 6 to 8 months post-infection.
The study reveals that anti-SARS-CoV-2 antibodies induced by the mRNA-1273 vaccine remain active for at least six months after receiving the second dose. The observations made in the study clearly highlight the importance of the Moderna vaccine in combating the COVID-19 pandemic.
The scientists are currently monitoring immune responses beyond six months. They are also investigating whether a booster dose can extend the duration and robustness of antibody responses against newly emerged variants of SARS-CoV-2.