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 The Oxford University trial was launched last April, three months
after Britain became the first country to approve what are known as
challenge trials for humans involving COVID-19.
Its first phase, still ongoing, has focused on finding out how much
of the virus is needed to trigger an infection while the second will
aim to determine the immune response needed to ward one off, the
university said in a statement on Tuesday.
Researchers are close to establishing the weakest possible virus
infection that assures about half of people exposed to it get
asymptomatic or mild COVID-19.
They then plan to expose volunteers - all previously naturally
infected or vaccinated - to that dose of the virus's original
variant to determine what levels of antibodies or immune T-cells are
required to prevent an infection.
"This is the immune response we then need to induce with a new
vaccine," said Helen McShane, Oxford University Professor of
Vaccinology and the study's chief investigator.
The trial's findings will help make future vaccine development much
quicker and more efficient, the statement said.
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 Global immunologists have been seeking to
pinpoint the immune reaction that a vaccine must
produce to shield against the illness, known as
a correlate of protection. Once discovered, the
need for mass vaccine trials is greatly reduced.
Scientists have used human challenge trials for
decades to develop treatments against many
infectious diseases, but this is the first known
such research into COVID-19.
A drawback is the risk of harm to volunteers
contracting the disease but the university is
taking precautions.
Participants will need to be healthy and aged
18-30. They will be quarantined for at least 17
days and any who develop symptoms will be given
Regeneron's monoclonal antibody treatment
Ronapreve.
(Reporting by Ludwig Burger; editing by John
Stonestreet)
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