Right now, more than 450,000 people worldwide have
reportedly recovered from COVID-19, and that number keeps ticking up, according
to Johns Hopkins University's COVID-19 dashboard. That's good news, of course;
but just because someone has contracted and ultimately healed from the new
coronavirus, doesn't mean they're entirely exempt from re-infection. That's
where the issue of immunity comes into play—and currently, researchers and
scientists still aren't sure what the body's immune response to SARS-CoV-2 is,
and how long it might last.
For the most part, the word 'immunity' conjures up thoughts
of complete protection from an illness, but it's much more complicated than
that, according to the Centers for Disease Control and Prevention. Generally
speaking, a person achieves immunity to a disease through the presence of
antibodies, or proteins produced by the body that can neutralize or even
destroy toxins or other disease carriers. "These are our 'attack
mechanisms' against 'invaders,'" Jaimie Meyer, MD, a Yale Medicine
infectious disease doctor and assistant professor of medicine at Yale School of
Medicine, tells Health. Those antibodies are also disease-specific, per the
CDC—it's why this year, for example, even if you got your flu shot, you have no
immunity against the current coronavirus outbreak.
Past that, immunity itself can be broken down into two
different categories: active immunity and passive immunity—and those
differences depend on how the body was introduced to whatever virus or bacteria
it developed antibodies for, and to what extent (and for how long) they can
prevent future disease. The good news: Both types can play a role in future
protection from (and even the potential treatment of) COVID-19.
What is active
immunity and how is it acquired?
The CDC explains that active immunity "results when
exposure to a disease organism triggers the immune system to produce antibodies
to that disease," and can happen one of two ways: Through infection with
the actual disease, which is known as natural immunity; or through a
vaccination (essentially, a killed or weakened form of the disease that won't
make someone ill, but will trigger the body to make antibodies), which is known
as vaccine-induced immunity.
Active immunity that results from either situation—natural
immunity or vaccine-induced immunity—will allow a person's immune system to
recognize the specific disease, if they ever come into contact with it again,
which will then trigger the body to produce the antibodies needed to fight it
off.
Per the CDC, active immunity is often longer-lasting and may
sometimes even provide life-long protection—but that's entirely based on the
disease itself. Immunity to the varicella virus (aka, chickenpox)—either via
acquiring the infection as a child or through a vaccine—can provide lifelong
immunity or long-lasting protection for up to 10 to 20 years, according to the
CDC. Whereas a yearly flu shot must be repeated annually, as it provides the
most protection within the first three months, and begins to lose most
effectiveness after six months.
It's also important to note that active immunity isn't
immediate—it can sometimes take several weeks to develop, which is why most
doctors, including the CDC, suggest getting your yearly flu shot by the end of
October, in order to have protection by the time flu season begins to pick up
in November or December.
While much more research needs to be done on immunity as it
pertains to COVID-19, Dr. Meyers says both natural immunity and vaccine-induced
immunity may provide protection against coronavirus—again, through infection by
the virus or a forthcoming vaccine. And while vaccine-induced immunity is still
a huge question mark—and will continue to be for at least another year until
more trials are completed—researchers are currently looking at the immunity
gained by those who have recovered from COVID-19.
During a World Health Organization media briefing on April
13, Michael Ryan, MD, MPH, executive director of the WHO's Health Emergencies
Programme, shares that it's still "unknown" whether those previously
infected with COVID-19 can be re-infected, and what type of immunity they have
against the virus. "One would expect that a person who generates a full-blown
immune response with detectable antibodies should have protection for a period
of time," Dr. Ryan said. "We just don't know what that period of time
is. We would expect that to be a reasonable period of protection, but it is
very difficult to say that with a new virus."
Maria Van Kerkhove, PhD, an emerging diseases expert and
technical lead on COVID-19 for the WHO, echoed this statement, after explaining
that preliminary studies out of China offered mixed findings on immunity.
"Right now, we don't have a full picture of what immunity looks
like," Dr. Van Herkhove said. "And until we do, we can't give a
complete answer."
Still, some experts—including the foremost COVID-19 resource
in the US, Dr. Anthony Fauci, the government's top infectious disease
specialist—feel confident that those exposed to and infected by the coronavirus
will develop some immunity. "If this virus acts like every other virus
that we know, once you get infected, get better, clear the virus, then you’ll
have immunity that will protect you against re-infection,” Dr. Fauci said in a
recent interview on The Daily Show.
What is passive
immunity and how is it acquired?
While active immunity occurs when an individual produces
antibodies to a disease through his or her own immune system, passive immunity
is provided when a person is given antibodies. This can happen in utero or
through antibody-containing blood products—such as immune globulin, or a
substance made from human blood plasma—administered when immediate protection
from a specific disease is needed. “For example, when a mother’s antibodies
cross the placenta to the fetus or when people are given antibodies as
treatment for rabies,” explains Dr. Meyer. Immune globulin can also provide
protection against hepatitis A in instances when a hepatitis A vaccine is not
recommended, per the CDC.
The major advantage to passive immunity—and the reason why
it's sometimes used as a treatment against diseases—is that it provides
immediate protection. But passive immunity doesn't last as long as active
immunity, and loses effectiveness within a few weeks or months, per the CDC.
Of course, this passive immunity may also be helpful when it
comes to COVID-19—primarily through the potential use of convalescent serum or
blood plasma collected from those who have previously recovered from COVID-19.
This means, according to Dr. Meyer, "giving antibodies from the blood of
people who have recovered from COVID-19 to people who are actively ill in order
to prevent complications and hasten recovery." But the use of convalescent
plasma isn't exactly new; it's also been used as a treatment option in a
variety of other infectious diseases, including Ebola, Middle East respiratory
syndrome (MERS), SARS, and even the H1N1 and H5N1 infections, according to
research presented in JAMA. That same research found that, for five
critically-ill patients with COVID-19, convalescent plasma treatment resulted
in "an improvement in clinical status" in all patients, concluding
that convalescent plasma may be a helpful treatment for those with critical
cases of COVID-19.
Convalescent plasma as treatment for COVID-19 specifically
is still being studied, and is not yet recommended as routine treatment—but
while it's not yet been approved for use by the US Food & Drug
Administration, the FDA did provide guidance to health care professionals and
investigators administering or studying the use of convalescent plasma for
treatment of COVID-19, according to a press release shared Monday, April 13. In
addition to those guidelines. the FDA also approved Johns Hopkins University to
test blood therapies for COVID-19 using plasma from recovering patients.
"Researchers hope to use the technique to treat critically-ill COVID-19
patients and boost the immune systems of health care providers and first
responders," researchers from Johns Hopkins University said in a press
release.
(Health.com)
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