Until recently, researchers had to rely on
statistical models, some of which estimated
that for every confirmed coronavirus case,
there were likely seven to 10 other people who
were infected but not counted. Now with the
arrival of blood antibody tests, scientists hope
the picture will come into sharper focus.
“I think we are beginning to get interesting
little rays of light” into how widespread
infections have been, but larger and more
rigorous studies will be needed to get a
better understanding, said Stephen Morse,
a Columbia University expert on the spread
of diseases.
Here is a guide to the studies that are emerging
and to some of the questions experts ask when
looking at them.
HOW DO THESE STUDIES WORK?
Researchers take blood samples, often just a
drop from a finger prick, from a group of people.
They aren’t looking for an active infection. They
are testing for antibodies — the markers of
infections that someone already had.
That helps show how many people were
infected, whether they knew it or not. Such
studies are widely used in public health to figure
out how many people have a range of diseases,
including measles, HIV and dengue.
WHY ARE THESE STUDIES IMPORTANT?
Not everyone with COVID-19 gets a diagnostic
test, which looks for signs of active infection
in throat and nose swabs. So the blood tests
can fill in gaps.