While there are differences between SARS-CoV-2 infection in macaques and humans, the findings, published in the journal Science, offer some of the first evidences that non-human primates can develop protective immunity to Covid-19.
According to the researchers, including Indian-origin scientist Abhishek Chandrashekar from Harvard Medical School in the US, one of the questions which remain unanswered is whether infection with SARS-CoV-2 results in protective immunity against re-exposure to the virus.
Citing an earlier study, they said macaques were found to be promising models for testing Covid-19 therapeutics, and to get answers to these questions.
In two current studies, the researchers explored whether initial exposure to SARS-CoV-2 protected against re-infection, and whether vaccination protected offered protection.
In the first study, they developed a macaque model of SARS-CoV-2 infection, which captured certain aspects of human infection.
The scientists then tested whether nine of the adult animals that had cleared the virus were immune to re-infection 35 days later.
According to the study, all nine animals showed little to no symptoms after re-challenge, and exhibited immune responses that protected against the second infection.
However, the scientists said additional research will be required to define the durability of natural immunity.
Rigorous clinical studies will be required to determine whether SARS-CoV-2 infection effectively protects against its re-exposure in humans, they said.
In the other study, including many of the same researchers, and led by Jingyou Yu from Harvard Medical School, the scientists designed prototypes of SARS-CoV-2 DNA vaccine candidates.
These prototypes expressed six different forms of the the novel coronavirus’ spike protein, which is used by the virus to bind and invade human cells.
According to the researchers, these vaccine candidates provide DNA that allows host cells to make their own spike proteins so as to generate antibody responses to it.
When the scientists vaccinated 35 adult macaques with these vaccines, in initial rounds, and later with booster doses, the animals exhibited similar immune responses to those recovering in the first study by Chandrashekar and his team.
When the vaccinated macaques were infected intranasally with SARS-CoV-2 six weeks later, the study reported levels of antibodies in their blood sufficient to neutralise the virus in two weeks’ time.
The researchers said these levels were similar to those seen in humans recovering from SARS-CoV-2 infection.
Protective immunity in the macaques, they said, is likely mediated by an immune system response similar to the one seen in the first study.
The scientists believe that their work could accelerate the development of vaccines, but said more research is needed to determine the optimal platforms for one suited for humans.