The novel coronavirus was
detected again for the second time last month after more than 160 South Koreans
recovered from medical supervision. This is the possibility that we know but
don't know that the virus got sick more than once. Most scientists say people
with covid-19 have some immunity to the virus that causes it. They don't know
whether to protect for a few months, a few years or a lifetime.
The immune system fights off
infection by producing antibodies that resist the invader. A range of genetic
and environmental factors, including diet and sleep patterns, often influence
the strength and longevity of these defenses. Immunity also depends on the pathogen.
For example, infection with the virus that causes measles can confer lifelong
immunity.
Data are scarce, but
preliminary studies suggest that antibodies can appear days or weeks after the
onset of symptoms. A study of 34 hospitalized cases in China found that both
patients developed antibodies within three days of the onset of symptoms in the
1980s. The rest developed two weeks after symptoms first appeared.
South Korean doctors involved
in the government's ongoing review believe the patients may have low levels of
the virus and failed diagnostic polymerase chain reaction or PCR tests. Later
in the disease, the virus sinks into the lungs, making it undetectable. They
say the virus has not been completely cleared from the body. When the symptoms
disappear, fragments of the virus remain in the body, but that doesn't mean a
person is contagious or that the disease will return.
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