A new study has shown that six in ten children are immune to COVID-19, despite never being infected by it.
Findings of the study published on GAVI.org, shows that children are far more likely than adults to have antibodies against COVID-19.
This might explain why they are often unaffected by the virus that causes COVID-19 or only have mild illness, the study shows.
An antibody is a protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen (such as coronaviruses). Antibodies recognise and latch onto antigens in order to remove them from the body.
According to the report, researchers publishing in Science looked at people who had never been exposed to the new coronavirus for pre-existing antibodies that bind to the spike protein on the surface of the SARS-CoV-2 virus.
They also looked at whether those antibodies had an effect on the way the SARS-CoV-2 virus infects cells.
The researchers found that roughly 5 per cent of 302 uninfected adult participants had antibodies that recognise the SARS-CoV-2 virus.
By comparison, as many as 62 per cent of uninfected children aged 6 to 16 years had antibodies, the age group in which antibodies to seasonal coronaviruses are most common.
In laboratory tests, they found that pre-existing antibodies also stopped the SARS-CoV-2 virus from entering cells.
The spike protein has two subunits S1 and S2, and the researchers found that S2 was most similar across coronaviruses and this is most likely where cross-reactive immunity stems from.
The researchers also suggested that investigating the S2 subunit could contribute to a universal vaccine against coronaviruses.
They noted that differentiating between pre-existing and new immunity to SARS-CoV-2 will be important in understanding response to a COVID-19 vaccine and susceptibility to the virus.
In the meantime, three major competitors have emerged in the international race to find a vaccine to counter the virus, which has infected over 60 million people globally.
U.S. pharmaceuticals giant Pfizer and its German partner BioNTech have announced that their vaccine is 95 per cent effective and that there were no safety concerns.
The companies are already applying for an emergency use authorisation from the U.S. Food and Drug Administration (FDA).
The U.S. pharmaceutical firm Moderna on November 16 announced that its COVID-19 vaccine candidate was 94.5 per cent effective.
Pharmaceutical giant AstraZeneca and the University of Oxford also said their newly developed COVID-19 vaccine is, on average, 70.4 per cent effective.
Like all vaccines, the one against COVID-19 is essentially expected to instruct the immune system to mount a defence, which is sometimes stronger than what would be provided through natural infection and comes with fewer health consequences.
There are more than 150 vaccine candidates around the world right now. Many of them will never make it out of the laboratory but the leading candidates are defying medical norms and promising a safe and efficient cure by the end of this year.