Unvaccinated healthy participants with no history of COVID were given an extremely low dosage of the original SARS-CoV-2 strain via nasal spray. The participants were then extensively observed in a quarantine unit, with frequent tests and samples collected to assess their viral response in a highly controlled and safe setting.

The researcher collected samples from tissue located midway between the nose and the throat, as well as blood samples from 16 volunteers. These samples were taken before the participants were exposed to the virus, to give a baseline measurement, and afterwards at regular intervals.

To their surprise, they found that despite all the volunteers being carefully exposed to the exact same dose of the virus in the same manner, not everyone ended up testing positive for COVID.

Researchers were able to divide the volunteers into three distinct infection groups, with only six out of the 16 volunteers developing typical mild COVID, testing positive for several days with cold-like symptoms.

Out of the ten volunteers who did not develop a sustained infection – suggesting that they were able to fight off the virus early on – three went on to develop an “intermediate” infection with intermittent single positive viral tests and limited symptoms.

The final seven volunteers remained negative on testing and did not develop any symptoms. This was the “abortive infection group”. This is the first confirmation of abortive infections, which were previously unproven.

In these people, they were able to identify cells stimulated by a key antiviral defence response in both the nose and the blood.

Called the “interferon” response, it’s one of the ways our bodies signal to our immune system to help fight off viruses and other infections. Surprisingly, this response was detected in the blood before it was detected in the nose, suggesting that the immune response spreads from the nose very quickly.

The researchers identified a specific gene called HLA-DQA2 at a much higher level in the volunteers who did not go on to develop infection and could therefore be used as a marker of protection.

The finding could paint a much more detailed picture of how our bodies react to a new virus, particularly in the first couple of days of an infection, which is crucial.

The results of the study would further help scientists create more effective vaccines against viral infections like COVID-19, and in a way, help us prep for the next pandemic.

[source:gavi.org]