Monoclonal antibodies are immune system proteins that are created in the laboratory, and can be specially designed and engineered to target Sars-CoV-2, the virus that causes Covid-19.

Such antibodies are also used to treat other diseases, such as cancer and asthma.

Their advantage lies in how they can be developed in a matter of months and produced in large batches. The effect of a single injection may last for a few weeks.

Assistant Professor October Sessions from the NUS Saw Swee Hock School of Public Health said a monoclonal antibody is able to inactivate the virus before it can cause an infection. Cells are engineered to produce this single antibody in large numbers to be delivered as a therapeutic.

This makes it different from other antibody treatments, such as utilising serum from patients who have recovered from the infection, he said. But antibodies can vary from person to person, making it difficult to predict their effectiveness.

Asked about the risks involved, Prof Sessions said the body of a person receiving a monoclonal antibodies treatment would not reject it as foreign as it looks like any other antibody produced by the body.

This means that the treatment could be used in a preventive manner, such as on people who have come into contact with a confirmed Covid-19 patient. "However, since it is not natively produced by the body, it will need to be administered at regular intervals like any other therapeutic agent," he added.

Professor Shiv Pillai, a medicine and health sciences and technology professor at Harvard Medical School, cautioned that it might be too expensive to use such a treatment as a preventive measure on a large scale.

He estimated the cost per dosage to be a few thousand dollars depending on the company producing it, and it has to be given every three weeks. "It would be most useful for those already infected - it would be overkill otherwise," he said.

Other companies overseas have also begun human trials for monoclonal antibodies.

American pharmaceutical company Eli Lilly and Co announced earlier this month that the first patients in its study were dosed at major medical centres in the US.

In China, a biopharmaceutical company called Junshi Biosciences said on Sunday that it has begun clinical trials on healthy volunteers for the monoclonal antibody it has developed. The study will be done at Huashan Hospital in Shanghai.