US biotechnology company's vaccine candidate protected mice from infection with SARS-CoV-2, the virus that causes COVID-19, according to a study published in the journal Nature on Wednesday.
The findings by scientists, including those from the National Institute of Allergy and Infectious Diseases (NIAID) in the US, show that the vaccine, known as mRNA-1273, induced neutralising antibodies in mice when given as two intramuscular injections of a 1-microgramme (mcg) dose three weeks apart.
Additional experiments found that mice given two injections of the 1-mcg dose and later challenged with SARS-CoV-2 virus either five or 13 weeks after the second injection were protected from viral replication in the lungs and nose, the researchers said.
Mice challenged seven weeks after only a single dose of 1 mcg or 10 mcg of mRNA-1273 were also protected against viral replication in the lung, they said.
NIAID Vaccine Research Center (VRC) scientists worked with investigators from the University of Texas at Austin to identify the atomic structure of the spike protein on the surface of the novel coronavirus.
This structure was used by Moderna in the development of the vaccine candidate, according to the researchers.
The latest study found that the investigational vaccine also induced robust CD8 T-cell responses in mice.
It did not induce the type of cellular immune response that has been linked to vaccine-associated enhanced respiratory disease (VAERD), according to the researchers.
This rare, allergic-type inflammation was seen in individuals vaccinated with a whole-inactivated respiratory syncytial virus (RSV) vaccine in the 1960s, they said.
The researchers explained that VAERD can occur when a vaccine induces an immune response that is not strong enough to protect against infection.
They vaccinated mice with sub-protective doses of mRNA-1273 and then challenged the mice with SARS-CoV-2.
The mice showed no evidence of enhanced lung pathology or excessive mucus production, indicating the vaccine did not cause enhanced disease, the researchers found.
The team noted that the data from these studies, combined with data from studies in nonhuman primates and Phase-1 clinical testing, support the evaluation of mRNA-1273 in clinical efficacy trials.
The researchers also explained how their prior research on a candidate MERS-CoV vaccine paved the way for a rapid response to the COVID-19 outbreak.