Scientists have assessed the novel coronavirus infection in monkeys and found that the immune system's T cells may contribute to protection against the virus if antibody responses are suboptimal, an advance which may aid in the development of vaccines and therapeutics for Covid-19.

The study, published in the journal Nature, shed light on the role of antibodies and immune cells in protection against SARS-CoV-2 -- the virus that causes Covid-19.

"In this study, we define the role of antibodies versus T cells in protection against Covid-19 in monkeys. We report that a relatively low antibody titre -- the concentration of antibodies in the blood -- is needed for protection," said study co-author Dan Barouch from Beth Israel Deaconess Medical Center (BIDMC) in the US.

"Such knowledge will be important in the development of next generation vaccines, antibody-based therapeutics, and public health strategies for Covid-19," Barouch said.

Earlier studies had suggested that SARS-CoV-2 infection protects rhesus macaques from re-exposure, following which Barouch and his colleagues purified and collected antibodies from the monkeys that had recovered from infection.

They administered the antibodies at various concentrations to 12 uninfected macaques and observed that protection against SARS-CoV-2 challenge was dose dependent.

According to the researchers, animals that received higher amounts of antibodies were protected more completely, while animals that received lower amounts of antibodies were protected less well.

Similarly, when they administered various concentrations of the purified antibodies to sick monkeys with active SARS-CoV-2 infection, those given higher doses demonstrated more rapid viral control.

In another set of experiments, the scientists evaluated the role of specific immune cells -- CD8+ T cells -- in contributing to protection against the virus by removing these cells from animals that had recovered from the infection.

When they removed these immune cells, it left the animals vulnerable to infection after re-exposure to SARS-CoV-2.

"Our data define the role of antibodies and T cells in protection against COVID-19 in monkeys. Antibodies alone can protect, including at relatively low levels, but T cells are also helpful if antibody levels are insufficient," said Barouch, who is also Professor of Medicine at Harvard Medical School.

"Such correlates of protection are important given the recent successful vaccine results from human trials, and the likelihood that these and other vaccines will become widely available in the spring," he added.

Barouch believes future vaccines may need to be licensed based on immune correlates rather than clinical efficacy.