Get to know 7 Coronaviruses that Infect Humans

Jakarta, CNN Indonesia - Corona Virus is  increasingly the concern of many parties after hundreds of people in Wuhan, China, have died. In addition, thousands of other people in several countries around the world are infected with this virus.

Credit : https://www.conwaymedicalcenter.com/news/coronavirus-what-you-need-to-know/

Head of the Eijkman Molecular Biology Institute, Prof. Amin Subandriyo said the corona virus that appeared in Wuhan,  China (2019-nCoV) is the 7th corona virus that infects humans.

Launching Medical News Today, the Corona virus was not the first time it was discovered and occurred in Wuhan. The true Corona virus was identified in 1937.

At that time researchers found the Corona virus found in the bodies of birds that have bronchitis infections. The first Corona virus has the ability to seriously destroy poultry stocks.

After the first incident, scientists have discovered that the Corona virus can infect mice, dogs, cats, turkeys, horses, pigs, and farm animals.

Launching the Centers for Disease Control and Prevention ( CDC ) of the United States, the Corona virus that attacks humans was only discovered in the 1960s.

While the latest Corona variant, 2019-nCoV is endemic and is a serious warning to the world. This decision was taken after the number of people continues to grow and human-to-human transmission outside China.

The name of this virus is actually a virus that is commonly found in animals. But, sometimes the corona virus that infects animals can spread to humans and become a new human corona virus. The corona virus that invaded humans was first identified in the mid-1960s.

MERS virus is transmitted from camels to humans. Meanwhile, the new corona virus found in China is suspected to be transmitted by snakes or bats. SARS is believed to be transmitted by ferrets to humans.

The corona virus that infects animals is divided into four main sub-groups known as alpha, beta, gamma, and delta. During this time, the corona virus that is transmitted from animals to humans is alpha and beta type corona.

So far there have been four alpha corona that have attacked humans, namely HCoV-229E; HCoV-NL63; HCoV-OC43; and HCoV-HKU1. As for Corona Beta, there have been three identified, SARS, MERS-CoV, and 2019-nCoV.

The Corona alpha virus is not as malignant as the corona beta virus. In fact, many people around the world are infected with this type of corona virus, as reported by the website of the health agency (CDC) United States (US).

Corona alpha only causes mild to moderate upper respiratory tract disease, such as the common cold. Corona alfa virus is usually only infects in a short time.

While SARS; MERS; and 2019-nCoV is a Corona beta virus that causes lower respiratory tract diseases such as pneumonia or bronchitis. This disease can take lives because it infects the lungs and makes it difficult for sufferers to breathe.

Difficulty in breathing makes the supply of oxygen in the body decreases and can eventually cause death.

Seven coronaviruses that are known to infect humans are:

1. HCoV-229E ( alpha coronavirus )

This virus was first reported to infect humans in the mid-1960s. Those infected with this virus are reported to have signs of the common cold. This virus is easier to attack children and the elderly. So far, transmission of this virus has not been reported to cause casualties, as reported by the Hindawi journal .


Realm          :     Riboviria
Kingdom     :     Orthornavirae
Phylum        :     Pisuviricota
Class            :     Pisoniviricetes
Order           :     Nidovirales
Family         :     Coronaviridae
Genus          :     Alphacoronavirus
Subgenus     :     Duvinacovirus
Species        :     Human coronavirus 229E

Source : https://en.wikipedia.org/wiki/Human_coronavirus_229E

2. HCoV-NL63 ( alpha coronavirus )

Human coronavirus NL63 (HCoV-NL63) is a species of coronavirus that was identified in late 2004 in a seven-month-old child with bronchiolitis in the Netherlands. The virus is an enveloped, positive-sense, single-stranded RNA virus which enters its host cell by the ACE2 receptor. Infection with the virus has been confirmed worldwide, and has an association with many common symptoms and diseases. Associated diseases include mild to moderate upper respiratory tract infections, severe lower respiratory tract infection, croup and bronchiolitis.

The virus is found primarily in young children, the elderly, and immunocompromised patients with acute respiratory illness. It also has a seasonal association in temperate climates. A study performed in Amsterdam estimated the presence of HCoV-NL63 in approximately 4.7% of common respiratory illnesses.The virus originated from infected palm civets and bats. HCoV-NL63 is one of seven known coronaviruses to infect humans, including HCoV-229E, HCoV-OC43, HCoV-HKU1, MERS-CoV, the original SARS-CoV (or SARS-CoV-1), and SARS-CoV-2. Estimates of its divergence from HCoV-229E are around 1000 years ago: it has likely circulated in humans for centuries.


Realm          :     Riboviria
Kingdom     :     Orthornavirae
Phylum        :     Pisuviricota
Class            :     Pisoniviricetes
Order           :     Nidovirales
Family         :     Coronaviridae
Genus          :     Alphacoronavirus
Subgenus     :     Setracovirus
Species        :     Human coronavirus NL63

Source : https://en.wikipedia.org/wiki/Human_coronavirus_NL63

3. HCoV-OC43 ( beta coronavirus )

This type of corona virus is a virus that usually causes flu. This is a more common corona virus variant in some parts of the world. Recent research shows this virus can cause severe lower respiratory tract disease in children.

The OC43 subtype (HCoV-OC43) is a more common human corona virus in some parts of the world. Recent research shows this virus can cause severe lower respiratory tract disease in children, NCBI reported.

Four HCoV-OC43 genotypes (A to D), have been identified with genotype D most likely arising from recombination. The complete genome sequencing of two genotype C and D strains and bootscan analysis shows recombination events between genotypes B and C in the generation of genotype D. Of 29 strains identified, none belong to the more ancient genotype A. Molecular clock analysis using spike and nucleocapsid genes dates the most recent common ancestor of all genotypes to the 1950s. Genotype B and C date to the 1980s. Genotype B to the 1990s, and genotype C to the late 1990s to early 2000s. The recombinant genotype D strains were detected as early as 2004.

Comparison of HCoV-OC43 with the most closely related strain of Betacoronavirus 1 species, bovine coronavirus, indicated that they had a most recent common ancestor in the late 19th century, with several methods yielding most probable dates around 1890, leading authors to speculate that an introduction of the former strain to the human population might have caused the 1889–1890 flu pandemic.

Realm            :     Riboviria
Kingdom       :     Orthornavirae
Phylum          :     Pisuviricota
Class              :     Pisoniviricetes
Order             :     Nidovirales
Family           :     Coronaviridae
Genus            :     Betacoronavirus
Species          :     Betacoronavirus 1
Subspecies     :     Human coronavirus OC43

Source : https://en.wikipedia.org/wiki/Human_coronavirus_OC43

4. HCoV-HKU1 ( beta coronavirus ),

This virus was discovered in 2005 in patients in Hong Kong. Citing  the  US National Institute of Health , at that time the virus infected 71-year-old grandfather who had just returned from Shenzhen, China.

Human coronavirus HKU1 (HCoV-HKU1) is a species of coronavirus which originated from infected mice. In humans, infection results in an upper respiratory disease with symptoms of the common cold, but can advance to pneumonia and bronchiolitis. It was first discovered in January 2005 in two patients in Hong Kong. Subsequent research revealed it has global distribution and earlier genesis.

The virus is an enveloped, positive-sense, single-stranded RNA virus which enters its host cell by binding to the N-acetyl-9-O-acetylneuraminic acid receptor. It has the Hemagglutinin esterase (HE) gene, which distinguishes it as a member of the genus Betacoronavirus and subgenus Embecovirus.

A trace-back analysis of SARS negative nasopharyngeal aspirates from patients with respiratory illness during the SARS period in 2003, identified the presence of CoV-HKU1 RNA in the sample from a 35-year-old woman with pneumonia.

Following the initial reports of the discovery of HCoV-HKU1, the virus was identified that same year in 10 patients in northern Australia. Respiratory samples were collected between May and August (winter in Australia). Investigators found that most of the HCoV-HKU1–positive samples originated from children in the later winter months.

The first known cases in the Western hemisphere were discovered in 2005 after analysing older specimens by clinical virologists at Yale-New Haven Hospital in New Haven, Connecticut who were curious to discover if HCoV-HKU1 was in their area. They conducted a study of specimens collected in a 7-week period (December 2001 – February 2002) in 851 infants and children. Specimens of nine children had human coronavirus HKU1.

These children had respiratory tract infections at the time the specimens were collected (in one girl so severe that mechanical ventilation was needed), while testing negative for other causes like Human respiratory syncytial virus (RSV), parainfluenza viruses (types 1–3), influenza A and B viruses, and adenovirus by direct immunofluorescence assay as well as human metapneumovirus and HCoV-NH by reverse transcription polymerase chain reaction (RT-PCR).

The researchers reported that the strains identified in New Haven were similar to the strain found in Hong Kong and suggested a worldwide distribution. These strains found in New Haven is not to be confused with HCoV-NH (New Haven coronavirus), which is a strain of Human coronavirus NL63.

In July 2005, six cases were reported in France. In these cases, French investigators utilized improved techniques for recovering the virus from nasopharyngeal aspirates and from stool samples.

Realm          :     Riboviria
Kingdom     :     Orthornavirae
Phylum        :     Pisuviricota
Class            :     Pisoniviricetes
Order           :     Nidovirales
Family         :     Coronaviridae
Genus          :     Betacoronavirus
Subgenus     :     Embecovirus
Species        :     Human coronavirus HKU1
Source : https://en.wikipedia.org/wiki/Human_coronavirus_HKU1


5. Severe Acute Respiratory Syndrome (SARS),

SARS-CoV is a severe acute respiratory syndrome and was first identified in China in November 2002. Scientists are also not sure what animal is the source of this virus transmission to humans.

It is estimated that the virus originates from bats which then spread to other animals, such as weasels. The first humans infected with this virus are in the Guangdong province, South China, as written on the WHO website .

This corona virus caused an outbreak with 8098 possible cases including 774 deaths in 2002-2003, or about 9 percent of patients infected with SARS died.

Credit : https://en.wikipedia.org/wiki/Severe_acute_respiratory_syndrome-related_coronavirus#/media/File:SARS-CoV_with_corona.jpg

There is no vaccine for SARS, although doctor Anthony Fauci mentioned that the CDC developed one and placed it in the US national stockpile. That vaccine, however, is a prototype and not field-ready as of March, 2020. Clinical isolation and quarantine remain the most effective means to prevent the spread of SARS. Other preventive measures include:

•     Hand-washing with soap and water, or use of alcohol-based hand sanitizer
•     Disinfection of surfaces of fomites to remove viruses
•     Avoiding contact with bodily fluids
•     Washing the personal items of someone with SARS in hot, soapy water (eating utensils, 
      dishes, bedding, etc.)
•     Keeping children with symptoms home from school
•     Simple hygiene measures
•     Isolating oneself as much as possible to minimize the chances of transmission of the virus

Many public health interventions were made to try to control the spread of the disease, which is mainly spread through respiratory droplets in the air. These interventions included earlier detection of the disease; isolation of people who are infected; droplet and contact precautions; and the use of personal protective equipment (PPE), including masks and isolation gowns. A 2017 meta-analysis found that for medical professionals wearing a medical or N-95 masks could reduce the chances of getting sick up to 80% compared to no mask. A screening process was also put in place at airports to monitor air travel to and from affected countries.

SARS-CoV is most infectious in severely ill patients, which usually occurs during the second week of illness. This delayed infectious period meant that quarantine was highly effective; people who were isolated before day five of their illness rarely transmitted the disease to others.

Although no cases have been identified since 2004, as of 2017, the CDC was still working to make federal and local rapid-response guidelines and recommendations in the event of a reappearance of the virus.

Realm            :     Riboviria
Kingdom        :     Orthornavirae
Phylum           :     Pisuviricota
Class               :     Pisoniviricetes
Order              :     Nidovirales
Family            :     Coronaviridae
Genus             :     Betacoronavirus
Subgenus        :     Sarbecovirus
Species           :     Severe acute respiratory syndrome-related coronavirus

Source : https://en.wikipedia.org/wiki/Severe_acute_respiratory_syndrome-related_coronavirus


6. Middle East Respiratory Syndrome-Corona Virus (MERS-CoV)

Middle East respiratory syndrome (MERS), also known as camel flu, is a viral respiratory infection caused by the MERS-coronavirus (MERS-CoV). Symptoms may range from none, to mild, to severe. Typical symptoms include fever, cough, diarrhea, and shortness of breath. The disease is typically more severe in those with other health problems.

MERS-CoV is a coronavirus believed to be originally from bats. However, humans are typically infected from camels, either during direct contact or indirectly. Spread between humans typically requires close contact with an infected person. Its spread is uncommon outside of hospitals.Thus, its risk to the global population is currently deemed to be fairly low. Diagnosis is by rRT-PCR testing of blood and respiratory samples.

As of 2020 there is no specific vaccine or treatment for the disease, but a number are being developed. The World Health Organization (WHO) recommends that those who come in contact with camels wash their hands and not touch sick camels. They also recommend that camel-based food products be appropriately cooked. Treatments that help with the symptoms and support body functioning may be used.

MERS-CoV was first identified in Saudi Arabia in 2012. As of August 1, 2013, there were 94 cases of MERSCoV and 47 died. Affected countries: Saudi Arabia, Jordan, Qatar, United Arab Emirates, United Kingdom, Germany, France, Italy and Tunisia.

WHO  calls current scientific evidence to show that dromedary camels are the main host for MERS-CoV. This camel is also an infectious animal MERS infection in humans. However, the exact role of the dromedary camel in virus transmission and the exact route of transmission is still unknown.

Specialty                  :    Infectious disease
Symptoms                :     Fever, cough, shortness of breath
Usual onset               :     2 to 14 days post exposure
Duration                   :     2012-2020
Causes                      :     MERS-coronavirus (MERS-CoV)
Risk factors              :     Contact with camels and camel products
Diagnostic method   :     rRT-PCR testing
Prevention                :     Hand washing, avoiding contact with camels and camel products
Treatment                 :     Symptomatic and supportive
Frequency                 :    2519 cases (as January 2020)
Deaths                       :    866 (35%)

Source : https://en.wikipedia.org/wiki/Middle_East_respiratory_syndrome

7. 2019 Coronavirus Novel or 2019-nCoV

The new type of corona virus, 2019-nCoV, can be transmitted from animals to humans and between humans. Symptoms experienced by people when infected with this virus include coughing, flu, fever, shortness of breath, difficulty breathing, respiratory failure, kidney failure to result in death.

Until now, the emergence of a new type of corona virus in downtown Wuhan, China, and the rate of development and mutation of the corona virus have not been associated with the effects of environmental changes such as reduced land cover and climate or weather changes.
Therefore, more research is needed to see whether there is a link between climate change with the development of the virus mutation

Citing Between , Corona Virus-nCoV 2019 officially announced the WHO, the World Health Organization, on January 9, 2020. The signs of the virus itself has been reported since mid-2019.

This new type of corona virus is associated with an outbreak of pneumonia that occurred in Wuhan City, Hubei Province, China. Until Friday (31/1) the number of victims died due to outbreaks of the new corona virus in China 213 people. while those infected with the virus reach nearly 2,000 people in China. While the total infected with the virus reached 9,356 people.

A number of cases related to people positively contracting the 2019-nCoV virus have been found in Vietnam, Thailand, the Philippines, Singapore, Japan, South Korea, Australia and the United States. (ex)

Credit : https://www.merdeka.com/peristiwa/ini-sebaran-data-kasus-covid-19-di-34-provinsi-indonesia.html

Apa itu Herd Immunity? Bisakah menghentikan penyebaran Virus Covid-19?

Anda mungkin pernah mendengar istilah "Herd Immunity" atau "kekebalan kelompok" yang digunakan sehubungan dengan wabah penyakit coronavirus .
Beberapa pemimpin - misalnya, Boris Johnson, perdana menteri Inggris - menyarankan itu mungkin cara yang baik untuk menghentikan atau mengendalikan penyebaran virus corona baru, yang menyebabkan COVID-19. “herd immunity” juga disebut kekebalan komunitas dan kelompok atau perlindungan.

“Herd Immunity” terjadi ketika begitu banyak orang dalam suatu komunitas menjadi kebal terhadap penyakit menular sehingga menghentikan penyebaran penyakit.
Ini dapat terjadi dalam dua cara:

1. Banyak orang terjangkit penyakit ini dan pada waktunya membangun respons kekebalan terhadapnya (kekebalan alami).
2. Banyak orang divaksinasi terhadap penyakit untuk mendapatkan kekebalan.

 “Herd Immunity” dapat bekerja melawan penyebaran beberapa penyakit. Ada beberapa alasan mengapa ini sering berhasil, ada juga banyak alasan mengapa “Herd Immunity” belum bekerja untuk menghentikan atau memperlambat penyebaran SARS-CoV-2 atau COVID-19, penyakit yang disebabkan oleh infeksi virus corona baru.

Bagaimana cara kerjanya?
Ketika sebagian besar populasi menjadi kebal terhadap suatu penyakit, penyebaran penyakit itu akan melambat atau berhenti.
Banyak infeksi virus dan bakteri menyebar dari orang ke orang. Rantai ini rusak ketika kebanyakan orang tidak mendapatkan atau menularkan infeksi.
Ini membantu melindungi orang yang tidak divaksinasi atau yang memiliki sistem kekebalan berfungsi rendah dan dapat mengembangkan infeksi lebih mudah, seperti:

• orang tua
• bayi 
• anak muda
• wanita hamil
• orang dengan sistem kekebalan yang lemah
• orang dengan kondisi kesehatan tertentu 

Statistik “Herd Immunity” Untuk beberapa penyakit, “Herd Immunity” dapat mulai berlaku ketika 40 persen orang dalam suatu populasi menjadi kebal terhadap penyakit, seperti melalui vaksinasi. Tetapi dalam kebanyakan kasus, 80 hingga 95 persen populasi harus kebal terhadap penyakit untuk menghentikan penyebarannya.
Sebagai contoh, 19 dari setiap 20 orang harus memiliki vaksinasi campak untuk “Herd Immunity” agar diberlakukan dan menghentikan penyakit. Ini berarti bahwa jika seorang anak terkena campak, semua orang di populasi ini kemungkinan besar telah divaksinasi, telah membentuk antibodi, dan kebal terhadap penyakit untuk mencegah penyebaran lebih lanjut.
Tujuan dari “Herd Immunity” adalah untuk mencegah orang lain menangkap atau menyebarkan penyakit menular seperti campak.
Namun, jika ada lebih banyak orang yang tidak divaksinasi di sekitar anak yang menderita campak, penyakit ini dapat menyebar dengan lebih mudah karena tidak ada “Herd Immunity”.
Untuk memvisualisasikan ini, bayangkan seseorang tanpa kekebalan sebagai titik merah yang dikelilingi oleh titik-titik kekebalan kuning. Jika titik merah tidak dapat terhubung ke titik merah lainnya, ada “Herd Immunity”.
Persentase orang yang harus memiliki kekebalan untuk memperlambat atau menghentikan penyakit menular secara aman disebut "ambang batas “Herd Immunity”."

Kekebalan alami
Kekebalan alami terjadi ketika Anda menjadi kebal terhadap penyakit tertentu setelah tertular. Ini memicu sistem kekebalan Anda untuk membuat antibodi terhadap kuman yang menyebabkan infeksi di dalam diri Anda. Antibodi seperti pengawal khusus yang hanya mengenali kuman tertentu.
Jika Anda berkontraksi lagi, antibodi yang menangani kuman sebelumnya dapat menyerang sebelum menyebar dan membuat Anda sakit. Misalnya, jika Anda menderita cacar air saat kecil, kemungkinan besar Anda tidak akan mendapatkannya lagi, bahkan jika Anda bersama seseorang.
Kekebalan alami dapat membantu menciptakan “Herd Immunity”, tetapi tidak berhasil sebaik vaksinasi. Ada beberapa alasan untuk ini:

• Setiap orang harus terkena penyakit itu sekali untuk menjadi kebal.
• Mengidap penyakit dapat memiliki risiko kesehatan, terkadang serius.
• Anda mungkin tidak tahu apakah Anda mengidap penyakit tersebut atau apakah Anda kebal terhadapnya.

Apakah “Herd Immunity” bekerja?
“Herd Immunity” memang bekerja untuk beberapa penyakit. Orang-orang di Norwegia berhasil mengembangkan setidaknya sebagian kekebalan terhadap virus H1N1 ( flu babi ) melalui vaksinasi dan kekebalan alami.
Demikian pula, di Norwegia, influenza diproyeksikan menyebabkan lebih sedikit kematian pada tahun 2010 dan 2011 karena lebih banyak penduduk yang kebal terhadapnya.
“Herd Immunity” dapat membantu menghentikan penyebaran penyakit, seperti flu babi, dan pandemi lainnya di seluruh negara. Tapi itu bisa berubah tanpa ada yang tahu. Juga, itu tidak selalu menjamin perlindungan terhadap penyakit apa pun.
Bagi kebanyakan orang sehat, “Herd Immunity” bukanlah alternatif yang baik untuk mendapatkan vaksinasi.
Tidak setiap penyakit yang memiliki vaksin dapat dihentikan oleh “Herd Immunity”. Misalnya, Anda dapat terkena tetanus dari bakteri di lingkungan Anda. Anda tidak kena dari orang lain, jadi “Herd Immunity” tidak bekerja untuk infeksi ini. Mendapatkan vaksin adalah satu-satunya perlindungan.
Anda dapat membantu membangun “Herd Immunity” terhadap penyakit tertentu di komunitas Anda dengan memastikan Anda dan keluarga Anda memiliki vaksinasi terbaru. “Herd Immunity” mungkin tidak selalu melindungi setiap individu di komunitas, tetapi bisa membantu mencegah penyakit yang meluas.

COVID-19 dan “Herd Immunity”
Jeda sosial dan sering mencuci tangan saat ini adalah satu-satunya cara untuk membantu mencegah Anda dan orang-orang di sekitar Anda tertular dan berpotensi menyebarkan SARS-CoV-2, virus yang menyebabkan COVID-19.
Ada beberapa alasan mengapa “Herd Immunity” bukan jawaban untuk menghentikan penyebaran coronavirus baru: 

1. Belum ada vaksin untuk SARS-CoV-2. Vaksinasi adalah cara teraman untuk mempraktikkan “Herd Immunity” dalam suatu populasi.
2. Penelitian untuk antivirus dan obat lain untuk mengobati COVID-19 sedang berlangsung.
3. Para ilmuwan tidak tahu apakah Anda dapat mengontrak SARS-CoV-2 dan mengembangkan COVID-19 lebih dari sekali.
4. Orang yang mengontrak SARS-CoV-2 dan mengembangkan COVID-19 dapat mengalami efek samping yang serius. Kasus yang parah dapat menyebabkan kematian.
5. Dokter belum tahu persis mengapa beberapa orang yang mengontrak SARS-CoV-2 mengembangkan COVID-19 yang parah, sementara yang lain tidak.
6. Anggota masyarakat yang rentan, seperti orang dewasa yang lebih tua dan orang-orang dengan beberapa kondisi kesehatan kronis, dapat menjadi sangat sakit jika mereka terkena virus ini.
7.  Kalau tidak, orang yang sehat dan lebih muda dapat menjadi sangat sakit dengan COVID-19.
8. Rumah sakit dan sistem perawatan kesehatan mungkin terbebani jika banyak orang mengembangkan COVID-19 secara bersamaan. 

“Herd Immunity” untuk COVID-19 di masa depan
Para ilmuwan saat ini sedang mengerjakan vaksin untuk SARS-CoV-2. Jika kita memiliki vaksin, kita mungkin dapat mengembangkan “Herd Immunity” terhadap virus ini di masa depan. Ini berarti mendapatkan SARS-CoV-2 dalam dosis tertentu dan memastikan mayoritas populasi dunia divaksinasi.
Hampir semua orang dewasa, remaja, dan anak-anak yang sehat perlu divaksinasi untuk memberikan “Herd Immunity” bagi orang-orang yang tidak bisa mendapatkan vaksin atau yang terlalu sakit untuk secara alami kebal terhadapnya.
Jika Anda divaksinasi dan membangun kekebalan terhadap SARS-CoV-2, kemungkinan besar Anda tidak akan tertular virus atau menularkannya.
Garis bawah
“Herd Immunity” adalah perlindungan komunitas atau kelompok yang terjadi ketika sejumlah kritis populasi kebal terhadap penyakit tertentu. Ini dapat membantu menghentikan atau memperlambat penyebaran penyakit menular seperti campak atau flu babi.
Cara teraman untuk mendapatkan kekebalan adalah melalui vaksinasi. Anda juga bisa mendapatkan kekebalan alami dengan mengontrak penyakit dan membangun respons kekebalan terhadapnya.
“Herd Immunity” bukan jawaban untuk menghentikan penyebaran SARS-CoV-2, coronavirus baru yang menyebabkan COVID-19. Setelah vaksin dikembangkan untuk virus ini, membangun “Herd Immunity” adalah salah satu cara untuk membantu melindungi orang-orang di komunitas yang rentan atau memiliki sistem kekebalan yang berfungsi rendah. 

Sumber : https://www.healthline.com