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2019 (COVID-19) pandemic
Mayo Clinic is following COVID-19 closely. Learn
more on Mayo Clinic News Network.

Coronaviruses are a family of

viruses that can cause
illnesses such as the common
cold, severe acute respiratory
syndrome (SARS) and Middle Coronavirus
East respiratory syndrome
(MERS). In 2019, a new
coronavirus was identified as the cause of a
disease outbreak that originated in China.

The virus is known as severe acute respiratory

syndrome coronavirus 2 (SARS-CoV-2). The
disease it causes is called coronavirus disease
2019 (COVID-19). In March 2020, the World
Health Organization (WHO) declared the COVID-
19 outbreak a pandemic.

Public health groups, including the U.S. Centers

for Disease Control and Prevention (CDC) and
WHO, are monitoring the COVID-19 pandemic
and posting updates on their websites. These
groups have also issued recommendations for
preventing and treating the virus that causes
COVID-19.

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Symptoms
Signs and symptoms of coronavirus disease
2019 (COVID-19) may appear 2 to 14 days after
exposure. This time after exposure and before
having symptoms is called the incubation period.
You can still spread COVID-19 before you have
symptoms (presymptomatic transmission).
Common signs and symptoms can include:

Fever

Cough

Tiredness

Early symptoms of COVID-19 may include a loss

of taste or smell.

Other symptoms can include:

Shortness of breath or difficulty breathing

Muscle aches

Chills

Sore throat

Runny nose

Headache

Chest pain

Pink eye (conjunctivitis)

Nausea

Vomiting

Diarrhea

Rash

This list isn't complete. Children have similar

symptoms to adults and generally have mild
illness.

The severity of COVID-19 symptoms can range

from very mild to severe. Some people may have
only a few symptoms. Some people may have no
symptoms at all, but can still spread it
(asymptomatic transmission). Some people may
experience worsened symptoms, such as
worsened shortness of breath and pneumonia,
about a week after symptoms start.

Some people experience COVID-19 symptoms

for more than four weeks after they're diagnosed.
These health issues are sometimes called post-
COVID-19 conditions. Some children experience
multisystem inflammatory syndrome, a syndrome
that can affect some organs and tissues, several
weeks after having COVID-19. Rarely, some
adults experience the syndrome too.

People who are older have a higher risk of

serious illness from COVID-19, and the risk
increases with age. People who have existing
medical conditions also may have a higher risk of
serious illness. Certain medical conditions that
may increase the risk of serious illness from
COVID-19 include:

Serious heart diseases, such as heart

failure, coronary artery disease or
cardiomyopathy

Cancer

Chronic obstructive pulmonary disease

(COPD)

Type 1 or type 2 diabetes

Overweight, obesity or severe obesity

High blood pressure

Smoking

Chronic kidney disease

Sickle cell disease or thalassemia

Weakened immune system from solid organ

transplants or bone marrow transplants

Pregnancy

Asthma

Chronic lung diseases such as cystic

fibrosis or pulmonary hypertension

Liver disease

Dementia

Down syndrome

Weakened immune system from bone

marrow transplant, HIV or some
medications

Brain and nervous system conditions, such

as strokes

Substance use disorders

This list is not complete. Other medical

conditions may increase your risk of serious
illness from COVID-19.

COVID-19 self-checker
Assess your symptoms on CDC’s
coronavirus self-checker tool and find out if
you’re a candidate for a COVID-19 test.

When to see a doctor

If you have COVID-19 signs or symptoms or
you've been in contact with someone diagnosed
with COVID-19, contact your health care provider
right away for medical advice. Your health care
provider will likely recommend that you get tested
for COVID-19. If you have emergency COVID-19
symptoms, such as trouble breathing, seek care
immediately. If you need to go to a hospital, call
ahead so that health care providers can take
steps to ensure that others aren't exposed.

If you have emergency COVID-19 signs and

symptoms, seek care immediately. Emergency
signs and symptoms can include:

Trouble breathing

Persistent chest pain or pressure

Inability to stay awake

New confusion

Pale, gray or blue-colored skin, lips or nail

beds — depending on skin tone

This list isn't complete. Let your health care

provider know if you are an older adult or have
chronic medical conditions, such as heart
disease or lung disease, as you may have a
greater risk of becoming seriously ill with COVID-
19.

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More Information

COVID-19 vs. flu: Similarities and

differences

COVID-19, cold, allergies and the flu

Unusual symptoms of coronavirus

Causes
Infection with severe acute respiratory syndrome
coronavirus 2, or SARS-CoV-2, causes
coronavirus disease 2019 (COVID-19).

The virus that causes COVID-19 spreads easily

among people. Data has shown that the COVID-
19 virus spreads mainly from person to person
among those in close contact. The virus spreads
by respiratory droplets released when someone
with the virus coughs, sneezes, breathes, sings
or talks. These droplets can be inhaled or land in
the mouth, nose or eyes of a person nearby.

Sometimes the COVID-19 virus can spread when

a person is exposed to very small droplets or
aerosols that stay in the air for several minutes or
hours — called airborne transmission.

The virus can also spread if you touch a surface

with the virus on it and then touch your mouth,
nose or eyes. But the risk is low.

The COVID-19 virus can spread from someone

who is infected but has no symptoms. This is
called asymptomatic transmission. The COVID-
19 virus can also spread from someone who is
infected but hasn't developed symptoms yet. This
is called presymptomatic transmission.

It's possible to get COVID-19 more than once.

When a virus has one or more new mutations it’s

called a variant of the original virus. The omicron
(B.1.1.529) variant spreads more easily than the
original virus that causes COVID-19 and the
delta variant. However, omicron appears to
cause less severe disease. People who are fully
vaccinated can get breakthrough infections and
spread the virus to others. But the COVID-19
vaccines are effective at preventing severe
illness. This variant also reduces the
effectiveness of some monoclonal antibody
treatments. Omicron has a few major offshoots
(sublineages), including BA.5 and BA.2.12.1.
BA.5 made up about 88% of COVID-19 infections
that had genetic sequencing in the U.S. in
August, 2022, according to the CDC.

In April, the CDC downgraded the delta variant

from a variant of concern to a variant being
monitored. This means that the delta variant isn’t
currently considered a major public health threat
in the U.S.

Risk factors
Risk factors for COVID-19 appear to include:

Close contact with someone who has

COVID-19, especially someone with
symptoms

Being coughed or sneezed on by an

infected person

Being near an infected person when in an

indoor space with poor air flow

Complications
Although most people with COVID-19 have mild
to moderate symptoms, the disease can cause
severe medical complications and lead to death
in some people. Older adults or people with
existing medical conditions are at greater risk of
becoming seriously ill with COVID-19.

Complications can include:

Pneumonia and trouble breathing

Organ failure in several organs

Heart problems

A severe lung condition that causes a low

amount of oxygen to go through your
bloodstream to your organs (acute
respiratory distress syndrome)

Blood clots

Acute kidney injury

Additional viral and bacterial infections

More Information

Long-term effects of COVID-19

Prevention
The U.S. Food and Drug Administration (FDA)
has given emergency use authorization to some
COVID-19 vaccines in the United States. The
FDA has approved the Pfizer-BioNTech COVID-
19 vaccine, now called Comirnaty, to prevent
COVID-19 in people age 12 and older. The FDA
has given emergency use authorization to Pfizer-
BioNTech COVID-19 vaccines for ages 6 months
through 11 years.

The FDA has approved the Moderna vaccine,

now called Spikevax, to prevent COVID-19 in
people age 18 and older. The FDA has also
authorized the Moderna COVID-19 vaccine in
children ages 6 months through 17 years old.
The FDA has also authorized the Novavax
COVID-19, adjuvanted vaccine to prevent
COVID-19 in people age 12 and older.

Due to the risk of a potentially life-threatening

blood-clotting problem, the FDA is restricting use
of the Janssen/Johnson & Johnson vaccine to
certain people age 18 and older. Examples
include people who had a severe allergic reaction
after getting an mRNA COVID-19 vaccine and
people who can't get an mRNA COVID-19
vaccine due to limited access or personal or
religious concerns. If you get this vaccine, be
sure to understand the risks and symptoms of the
blood-clotting problem.

A vaccine can prevent you from getting the

COVID-19 virus or prevent you from becoming
seriously ill if you get the COVID-19 virus. In
addition, COVID-19 vaccination might offer better
protection than getting sick with COVID-19. A
recent study showed that unvaccinated people
who already had COVID-19 are more than twice
as likely as fully vaccinated people to get
reinfected with COVID-19.

After getting vaccinated, you can more safely

return to many activities you may not have been
able to do because of the pandemic. However, if
you are in an area with a high number of people
with COVID-19 in the hospital and new COVID-
19 cases, the CDC recommends wearing a mask
indoors in public. You're considered fully
vaccinated two weeks after you get a second
dose of an mRNA COVID-19 vaccine, after two
doses of the Novavax vaccine, or two weeks
after you get a single dose of the
Janssen/Johnson & Johnson COVID-19 vaccine.
You are considered up to date with your vaccines
if you have gotten all recommended COVID-19
vaccines, including booster doses, when you
become eligible.

An additional primary dose of a COVID-19

vaccine is recommended for people who are
vaccinated and might not have had a strong
enough immune response.

In contrast, a booster dose is recommended for

people who are vaccinated and whose immune
response weakened over time. Research
suggests that getting a booster dose can
decrease your risk of infection and severe illness
with COVID-19.

People who have a moderately or severely

weakened immune system should get an
additional primary shot and a booster shot.

The CDC recommends additional doses and

booster doses of COVID-19 vaccines in specific
instances:

Additional primary shot. The CDC

recommends an additional primary shot of
an mRNA COVID-19 vaccine for some
people with weakened immune systems,
such as those who have had an organ
transplant. People with weakened immune
systems might not develop enough
immunity after vaccination with two doses of
an mRNA COVID-19 vaccine or one dose of
the Janssen/Johnson & Johnson COVID-19
vaccine. An additional shot using an mRNA
COVID-19 vaccine might improve their
protection against COVID-19. This
recommendation for an additional mRNA
COVID-19 shot is for people ages 6 months
and older.

The additional primary shot should be given

at least four weeks after a second dose of
an mRNA COVID-19 vaccine or one dose of
the Janssen/Johnson & Johnson COVID-19
vaccine. The additional primary shot should
be the same brand as the other two mRNA
COVID-19 vaccine doses that were given. If
the brand given isn't known, either brand of
mRNA COVID-19 vaccine can be given as a
third dose.

Booster dose. These recommendations

differ by age, what vaccines you have been
given and the state of your immune system.
But in general, people can get the booster
shot at least two months after their last shot.
People who recently had a positive COVID-
19 test may think about waiting three
months after their symptoms started to get
the booster.

Kids ages 6 months through 5 years who

got the Moderna COVID-19 vaccine can get
an updated, called bivalent, Moderna
COVID-19 vaccine booster. The booster is
based on the original virus strain and two
omicron strains.

Kids age 5 who got the Pfizer-BioNTech

COVID-19 vaccine can only get the updated
Pfizer-BioNTech COVID-19 bivalent vaccine
booster.

People age 6 and older can choose

between the updated Pfizer-BioNTech and
the updated Moderna COVID-19 bivalent
vaccine boosters.

If you are age 18 or older, and got the

Janssen COVID-19 vaccine, you can get
either of the mRNA vaccine bivalent
boosters at least two months after your shot.
People 18 and older may also get a
Novavax booster based on the original virus
strain as a first booster at least six months
after their last shot.

Pregnant people can also get a COVID-19

booster dose.

People age 5 and older who have a

weakened immune system and have had all
recommended doses of the Moderna,
Pfizer-BioNTech or Novavax COVID-19
vaccines can get a booster dose of the
updated Pfizer-BioNTech or Moderna
COVID-19 bivalent vaccines.

The FDA has also authorized the monoclonal

antibodies tixagevimab and cilgavimab
(Evusheld) to prevent COVID-19 in some people
with weakened immune systems or a history of
severe reactions to a COVID-19 vaccine.

There are many steps you can take to reduce

your risk of infection from the COVID-19 virus
and reduce the risk of spreading it to others.
WHO and CDC recommend following these
precautions:

Get vaccinated. COVID-19 vaccines reduce

the risk of getting and spreading COVID-19.

Avoid close contact with anyone who is sick

or has symptoms.

Keep distance between yourself and others

when you're in indoor public spaces. This is
especially important if you have a higher risk
of serious illness. Keep in mind some
people may have COVID-19 and spread it to
others, even if they don't have symptoms or
don't know they have COVID-19.

Avoid crowds and indoor places that have

poor air flow (ventilation).

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 face mask in indoor public spaces if

you're in an area with a high number of
people with COVID-19 in the hospital and
new COVID-19 cases, whether or not you're
vaccinated. The CDC recommends wearing
the most protective mask possible that you'll
wear regularly, fits well and is comfortable.

Improve the air flow indoors. Open windows.

Turn on fans to direct air out of windows. If
you can't open windows, consider using air
filters. And turn on exhaust fans in your
bathroom and kitchen. You might also
consider a portable air cleaner.

Cover your mouth and nose with your elbow

or a tissue when you cough or sneeze.
Throw away the used tissue. Wash your
hands right away.

Avoid touching your eyes, nose and mouth.

Avoid sharing dishes, glasses, towels,

bedding and other household items if you're
sick.

Clean and disinfect high-touch surfaces,

such as doorknobs, light switches,
electronics and counters, regularly.

Stay home from work, school and public

areas and stay home in isolation if you're
sick, unless you're going to get medical
care. Avoid public transportation, taxis and
ride-hailing services if you're sick.

If you have a chronic medical condition and may

have a higher risk of serious illness, check with
your doctor about other ways to protect yourself.

Related information

COVID-19 vaccines: Get the facts

COVID-19 vaccine: Guidance from

Mayo Clinic

Comparing the differences between

COVID-19 vaccines

Different types of COVID-19 vaccines:

How they work

COVID-19 vaccine myths debunked

Travel
If you're planning to travel, first check the CDC
and WHO websites for updates and advice. The
CDC recommends that you wear a mask on
planes, buses, trains and other indoor public
transportation traveling to, within or out of the
U.S., as well as in places such as airports and
train stations. Use appropriate hand hygiene
when in public. You may also want to talk with
your health care provider if you have health
conditions that make you more susceptible to
respiratory infections and complications.

More Information

COVID-19 travel advice

COVID-19 vaccines

COVID-19 vaccines for kids: What you

need to know

Show more related information

By Mayo Clinic Staff

Diagnosis & treatment

Dec. 17, 2022

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Coronavirus disease 2019

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