British scientists are set to begin trials to assess the safety and effectiveness of two experimental coronavirus vaccines when inhaled.

Researchers at the Imperial College London and Oxford University would test the vaccines being developed by both the institutions by delivering them directly to the respiratory tract of human volunteers by inhalation through the mouth rather than being injected.

“We’ve evidence that delivering influenza vaccines via a nasal spray can protect people against flu as well as help to reduce the disease transmission. We’re keen to explore if this may also be the case for SARS-CoV-2 and whether delivering Covid-19 vaccines to the respiratory tract is safe and produces an effective immune response,” Dr Chris Chiu, Department of Infectious Disease, Imperial, who will lead the project, said in a statement.

A total of 30 people are expected to be recruited to the trials. For each vaccine, researchers will assess three dose levels (low, medium and high dose) with three volunteers per group (18 in total), followed by an additional six in each group at the best dose (12 total).

In addition to blood and nasal sample analyses, volunteers will undergo bronchoscopy to obtain samples from deeper within the lungs and monitor the effects in the lower respiratory tract. They will receive aerosolised vaccines through a nebulizer, which will deliver the vaccine as airborne droplets through a mouthpiece. With direct vaccine administration to the respiratory tract, based on previous studies, lower doses may be required than by intramuscular injections to induce protective responses.

In addition to blood being analysed for the presence of neutralising antibodies (Immunoglobulin G, or IgG) and T cells, which fight the virus and protect against re-infection, the team will analyse nasal samples for the presence of specialised antibodies found in the nose and throat, called IgA, which would indicate a more specialised and localised immune response to the virus.

The Imperial vaccine uses synthetic strands of genetic code based on the virus. Once injected into the muscle, the body's own cells are instructed to make copies of a spiky protein on the coronavirus. That is expected to trigger in turn an immune response so the body can fight off any future Covid-19 infection.

The Oxford vaccine though uses a harmless virus — a chimpanzee cold virus, to carry the coronavirus' spike protein into the body, which should trigger an immune response. Last week, Oxford temporarily paused its large-scale vaccination tests after one participant reported severe neurological symptoms. It was restarted on Sunday last.