How Do We Become Immune?
When germs enter your body, your immune system springs into action. Here's how it works:
- Bacteria and viruses like the one that causes COVID-19 have proteins called antigens on their surfaces. Each type of germ has its own unique antigen.
- White blood cells of your immune system make proteins called antibodies to fight the antigen. Antibodies attach to antigens the way a key fits into a lock, and they destroy the invading germ.
- Once you've been exposed to a virus, your body makes memory cells. If you're exposed to that same virus again, these cells recognize it. They tell your immune system to make antibodies against it.
Vaccines work in much the same way. They expose your body to an antigen that trains your immune system to fight that germ in the future. Because vaccines contain weakened or killed versions of viruses, you become immune without getting sick.
Why is herd immunity important?
Herd immunity occurs when a large portion of a community
(the herd) becomes immune to a disease, making the spread of disease from
person to person unlikely. As a result, the whole community becomes protected —
not just those who are immune.
Often, a percentage of the population must be capable of getting
a disease in order for it to spread. This is called a threshold proportion. If
the proportion of the population that is immune to the disease is greater than
this threshold, the spread of the disease will decline. This is known as the
herd immunity threshold.
What percentage of a community needs to be immune in order
to achieve herd immunity? It varies from disease to disease. The more
contagious a disease is, the greater the proportion of the population that
needs to be immune to the disease to stop its spread. For example, the measles
is a highly contagious illness. It's estimated that 94% of the population must
be immune to interrupt the chain of transmission.
How is herd immunity achieved?
There are two paths to herd immunity for COVID-19 — vaccines
and infection.
Vaccines
A vaccine for the virus that causes COVID-19 would be an
ideal approach to achieving herd immunity. Vaccines create immunity without
causing illness or resulting complications. Herd immunity makes it possible to
protect the population from a disease, including those who can't be vaccinated,
such as newborns or those who have compromised immune systems. Using the
concept of herd immunity, vaccines have successfully controlled deadly
contagious diseases such as smallpox, polio, diphtheria, rubella and many
others.
Reaching herd immunity through vaccination sometimes has
drawbacks, though. Protection from some vaccines can wane over time, requiring
revaccination. Sometimes people don't get all of the shots that they need to be
completely protected from a disease.
In addition, some people may object to vaccines because of
religious objections, fears about the possible risks or skepticism about the
benefits. People who object to vaccines often live in the same neighborhoods or
attend the same religious services or schools. If the proportion of vaccinated
people in a community falls below the herd immunity threshold, exposure to a
contagious disease could result in the disease quickly spreading. Measles has
recently resurged in several parts of the world with relatively low vaccination
rates, including the United States. Opposition to vaccines can pose a real
challenge to herd immunity.
Natural infection
Herd immunity can also be reached when a sufficient number
of people in the population have recovered from a disease and have developed
antibodies against future infection. For example, those who survived the 1918
flu (influenza) pandemic were later immune to infection with the H1N1 flu, a
subtype of influenza A. During the 2009-10 flu season, H1N1 caused the respiratory
infection in humans that was commonly referred to as swine flu.
However, there are some major problems with relying on
community infection to create herd immunity to the virus that causes COVID-19.
First, it isn't yet clear if infection with the COVID-19 virus makes a person
immune to future infection.
Research suggests that after infection with some
coronaviruses, reinfection with the same virus — though usually mild and only
happening in a fraction of people — is possible after a period of months or years.
Further research is needed to determine the protective effect of antibodies to
the virus in those who have been infected.
Even if infection with the COVID-19 virus creates
long-lasting immunity, a large number of people would have to become infected
to reach the herd immunity threshold. Experts estimate that in the U.S., 70% of
the population — more than 200 million people — would have to recover from
COVID-19 to halt the epidemic. If many people become sick with COVID-19 at
once, the health care system could quickly become overwhelmed. This amount of
infection could also lead to serious complications and millions of deaths,
especially among older people and those who have chronic conditions.
How can you slow the transmission of COVID-19?
Until a COVID-19 vaccine is developed, it's crucial to slow
the spread of the COVID-19 virus and protect individuals at increased risk of
severe illness, including older adults and people of any age with underlying
health conditions. To reduce the risk of infection:
Avoid large events and mass gatherings.
Avoid close contact (within about 6 feet, or 2 meters) with
anyone who is sick or has symptoms.
Stay home as much as possible and keep distance between
yourself and others (within about 6 feet, or 2 meters) if COVID-19 is spreading
in your community, especially if you have a higher risk of serious illness.
Keep in mind some people may have the COVID-19 virus and spread it to others,
even if they don't have symptoms or don't know they have COVID-19.
Wash your hands often with soap and water for at least 20
seconds, or use an alcohol-based hand sanitizer that contains at least 60%
alcohol.
Wear a cloth face covering in public spaces, such as the
grocery store, where it's difficult to avoid close contact with others, especially
if you're in an area with ongoing community spread. Only use nonmedical cloth
masks — surgical masks and N95 respirators should be reserved for health care
providers.
Cover your mouth and nose with your elbow or a tissue when
you cough or sneeze. Throw away the used tissue.
Avoid touching your eyes, nose and mouth.
Avoid sharing dishes, glasses, bedding and other household
items if you're sick.
Clean and disinfect high-touch surfaces, such as doorknobs,
light switches, electronics and counters, daily.
Stay home from work, school and public areas if you're sick,
unless you're going to get medical care. Avoid public transportation, taxis and
ride-sharing if you're sick.
Thanks https://www.mayoclinic.org/,https://www.webmd.com/
Could Herd Immunity Protect Us?
Herd immunity happens when a large part of the population -- the herd -- is immune to a virus. This can happen either because these people got vaccinated or had already been infected. Herd immunity makes it harder for a virus to spread. So even those who haven't been sick or vaccinated have some protection.
The more contagious a virus is, the more people need to be immune for herd immunity to kick in. The SARS-CoV-2 virus is so contagious that experts estimate about 70% of people in a community will need to be immune to have herd protection. That number might be hard to get to without a vaccine or a whole lot of people getting sick.
If You've Had COVID-19, Are You Immune?
Health experts don't know whether we really become immune to COVID-19 after we're infected. And if we do have immunity, we don't know how long it might last. Thus far, there have been only a few incidents of confirmed re-infections. With two cases, it appears the patients were re-infected by the same strain, while the third was infected with a slightly different strain of the virus.
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