Young Astronomers Blog, Volume 29, Number 11.
A pandemic has engulfed the world! Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a virus that can produce a respiratory disease called COVID-19.
Viruses
A virus is a microscopic germ made up of genetic material (DNA or RNA. It is covered by a capsid (shell) of protein. It could also have a fat-like lipid membrane. Most viruses contain RNA. Some of these are called retroviruses that “reverse transcribe” RNA back to DNA. Viruses are small, some tens to hundreds of nanometers in diameter, which is a fraction the size of human blood cells. Most viruses can only be viewed through electron microscopes and not through ordinary microscopes.
Is a virus alive? Scientists are not sure. Viruses are made of genetic material, but they do not divide like cells, rather they are “constructed” within a host cell. Viruses come in different shapes including rod-like, spherical, or helical. Some viruses, including the coronavirus, have spike proteins that are used to attach to a host cell.
A virus cannot reproduce by itself. When outside a target cell, a virus is known as a virion. Once a virus identifies a target host cell, it either enters the cell or releases its genetic material into the cell. When it does, it takes over the cell and uses the cell’s genetic material to reproduce, making many copies of itself. This process can follow one or two distinct paths.
- The Lytic Cycle is where the cell breaks apart (lysis) and the new copies of the virus pour out of the cell. The copies then find more host cells and continue the process.
- The Lysogenic Cycle is where the viral genetic material is incorporated into the cell itself and multiply as the host cells replicate. The virus can remain dormant until something activates it, and it then goes through the Lytic Cycle.
The body’s immune systems attack the invading virus. The innate immune system is always active and quickly attacks invading germs providing the body’s first line of defense. After a few days to a week or so, the adaptive immune system becomes active and produces “B-cells” and “T-cells” to combat the virus. These cells are known as lymphocytes, a form of white blood cells also known as agranulocytes.
- B-cells (Bone marrow lymphocytes) are formed in the bone marrow and are released into the blood stream. They are activated when they recognize foreign material on a virus known as antigens. The B-cells produce Y structure proteins called antibodies, which bind to the targeted virus’ antigens. Antibodies can last for an extended time providing a longer term “immunity” to a specific virus.
- T-cells (Thymus lymphocytes) form in the bone marrow but mature in the thymus. There are different types of T-cells including T Helper cells that facilitate the activity of other T-cells and B-cells and T Cytotoxic cells that directly attack invading viruses by destroying those identified by antibodies.
There are also B-cells and T-cells called memory cells that “remember” certain viruses and can quickly respond to a reinfection.
The body also produces pyrogens that result in a higher body temperature (a fever). The fever, although uncomfortable, helps to fight the virus by slowing down its replication.
Tests for a virus look for two different things.
- Some tests determine if a person is currently infected by searching for the virus itself.
- Other tests tell if a person was infected in the past, and could have immunity from further infection, by looking for antibodies that were produced in response to a previous infection.
For many viruses, the goal is to render them inactive. There are five ways in which this can happen.
- Herd Immunity occurs when a large portion of the population (say 70% or more) becomes immune to the virus. The virus stops spreading easy and will, hopefully, die out.
- Control occurs when the instances of a virus (and its disease) are reduced to acceptable levels. Mumps and Chickenpox are examples of diseases that are almost fully controlled.
- Elimination is when a virus disappears from a geographical area but is not forgotten. Measles is a good example and has been virtually eliminated in the United States. However, it is still out there, and the measles vaccine is required to keep it in check.
- Eradication is when a virus essentially disappears worldwide, although this rarely happens. One prime example is smallpox, a disease that was all too common for many years but has now been wiped off the planet.
- Extinction is when the virus no longer exists anywhere.
Vaccines
To protect people from viruses, vaccines have been developed. Vaccines not only protect individuals from a virus, but they also render a virus inactive when a large percent of the population becomes immune. Vaccines cause the immune system to develop antibodies to fight the virus. There are different types of vaccines, as outlined by the World Health Organization (WHO).
- {Protein} Subunit vaccines use a portion (subunit) of a virus.
- Whole virus vaccines use weaken forms of the virus (live attenuated vaccines) or forms that cannot replicate (inactivated vaccines).
- Viral Vector vaccines (e.g., the adenovirus cold vaccines) use a modified version of a different and harmless virus.
- Nucleic acid vaccines (mRNA vaccines) contain DNA or RNA genetic material, which are used to create harmless versions of the virus proteins.
Although vaccines can be highly effective, they typically take years to develop. The normal process, as described by the CDC, goes through several stages. The first two can take 1 to 2 years each. The clinical trials can take as much as 15 years or longer.
- Exploration, where potential vaccines are identified.
- Pre-clinical, where potential vaccines are testing in the lab and in animals.
- Clinical development involves the testing on humans.
- Phase I with fewer than one hundred people.
- Phase II with several hundred people.
- Phase III with several thousand people.
- Regulatory review and approval by the FDA and CDC.
- Manufacturing, where the vaccine is produced for widespread usage.
- Quality control, which is used to ensure the vaccine is effective and safe.
In some situations, a vaccine can be authorized for emergency use before becoming approved. We’ve seen this with the Covid-19 vaccines. Three of which have been authorized, but not yet approved as of August 2021.
As with any vaccine, there is a trade-off between possible side effects/risk of the vaccine and effects/risk of the virus/disease the vaccine is designed to prevent. Generally, the negative effects of the virus/disease (far) out way the side effects of the vaccine. In other words, the disease is (far) worse than the vaccine. Vaccine safety is a primary concern of both the FDA, who initially authorizes and approves the vaccine and the CDC, who develops guidelines for its use. Adverse reactions to vaccines are monitored and tracked through the Vaccine Adverse Event Reporting System (VAERS). So, once authorized or approved, a vaccine is continually monitored for possible ill effects.
Vaccines don’t always last forever. The level of immunity from many vaccines wain over time.
- For some viruses such as the flu, vaccines are only around 50% effective and getting the flu does not lead to future immunity. Flu vaccines can help mitigate the spread, but people will still get the flu each year. The flu mutates so much from year to year, that an annual flu shot is usually necessary.
- Only the other hand, vaccines for diseases such as the Measles and Chickenpox are well over 90% effective and those that contracted these diseases are immune. This allows for these diseases to be controlled, eliminated, and possibly eradicated. For those who received the vaccine, booster shots might still be required. One measles vaccine will typically last a lifetime. However, the tetanus vaccine requires a booster dose every ten years.
Vaccines have been very successful in virtually eliminating diseases such as smallpox, polio, and measles. In fact, the smallpox vaccine was the first vaccine developed.
Smallpox
Smallpox was one of the deadliest diseases in history. It appeared a few thousand years ago and, in the twentieth century, was responsible for around 300 million fatalities. Thirty percent of those infected with smallpox died and many who recovered suffered from disfigurement. It is also thought to have wiped out 90% of the indigenous Americans.
For many years, smallpox was fought through inoculations (aka variolations) where a mild form of the disease was introduced into a patient who then develop immunity. This approach did have its drawbacks. The patients could spread the disease further and a small percentage (roughly 2%) died. Yet, it was better than contracting a stronger version of the disease and risk a 30% fatality rate. Things changed in 1796 when Edward Jenner discovered that patients infected with cowpox would develop an immunity to smallpox. He soon published his results as “An inquiry into the causes and effects of the variolae vaccinae: a disease discovered in some of the western counties of England, particularly Gloucestershire, and known by the name of the cow pox” and coined the term vaccination.
It still took many years for smallpox to be eradicated. Vaccinations slowly caught on and by the late 1800s and early 1900s they were required in some locations.
Then, as now, vaccinations were met by hesitancy. Organizations, such as The Anti Vaccination Society of America (1879), were founded to combat vaccination requirements. The most famous incident involved Henning Jacobson, who during a 1902 smallpox outbreak in Boston, refused to be vaccinated. His case resulted in the 1905 Supreme Court Jacobson v. Massachusetts ruling that the vaccine could be made mandatory. An additional case in 1922, Zucht v. King, affirmed that schools could require vaccinations.
By the mid-twentieth century the smallpox vaccine was mandated throughout most of the country, and smallpox vanished from the U.S. by 1949. Although, at the time, it was still very prevalent in other parts of the world. In 1967, the World Health Organization (WHO) undertook a campaign to eliminate smallpox worldwide. The last reported cased occurred in 1977 and on May 8, 1980, the WHO declared smallpox eradicated.
Polio
Although, probably an ancient disease, Polio was prevalent in the United States in the early to mid-1900s. In most cases Polio caused flu like symptoms, but in some it resulted in breathing difficulties and paralysis. The most famous case was Franklin Roosevelt, who developed polio in 1921 and was paralyzed for the rest of his life. By the early 1950s Polio, because it mostly infected young children, was feared by many parents.
In 1954, Jonas Salk developed the first Polio vaccine, which was used in a large-scale test and then administered to children throughout the country. Unfortunately, a bad batch resulted in a few deaths and the vaccinations were halted. In the early 1960s, the vaccinations began again using an alternative oral vaccine developed by Albert Sabin. As of the year 2000, Sabin’s vaccine has been replaced by a vaccine delivered by a shot. The last polio case in the U.S. was in 1979. However, the CDC still recommends children receive the polio vaccine. In 1988, the WHO began a program to eradicate polio worldwide. This effort is still ongoing.
Childhood Diseases
Measles, along with other childhood disease such as the Mumps and Chickenpox, were very common in the early 1950s. Technically, there are two forms of the “Measles” including Rubella (aka the German Measles). Most children born before the late 1950s probably contracted one or more of these diseases.
John Elders and Thomas Peebles were able to isolate the first measles virus in 1954. By 1963, they and others had developed the first measles vaccine. In 1967, Maurice Hilleman created the first Mumps vaccine based on his work that began with his daughter’s case of mumps in 1963. By the early 1970s, the mumps and measles vaccines were combined by Merck into the MMR vaccine used today for measles, mumps, and rubella. A chickenpox vaccine was first developed in the 1970s. It was licensed for use in the United States in 1995 and incorporated into the MMRV vaccine in 2005.
Today, the CDC recommends that children be vaccinated against these diseases. Younger children can receive the MMRV vaccine, which protects against all three. Older children and adults can get the MMR vaccine, which protects against Measles and Mumps.
Selected Sources and Further Reading (Viruses)
Regina Bailey. “Anatomy and Structure of Viruses.” ThoughtCo, Feb. 11, 2020, thoughtco.com/viruses-373893. https://www.thoughtco.com/viruses-373893
Sally Robertson, B.Sc. “What is a Virus?” News Medical Life Sciences. (Accessed August 17, 2021). https://www.news-medical.net/health/What-is-a-Virus.aspx
Lotti Tajouri. “What is a virus? How do they spread? How do they make us sick?” The Conversation. March 12, 2020. https://theconversation.com/what-is-a-virus-how-do-they-spread-how-do-they-make-us-sick-133437
“Germs Movie for Kids Virus & Bacteria Introduction.” Makemegenius/YouTube. October 13, 2012. https://www.youtube.com/watch?v=7D0eIsuZC3w
“Viruses: Molecular Hijackers.” Professor Dave Explains/YouTube. October 19, 2017. https://www.youtube.com/watch?v=wUgEhfo_qxU
David M. Modine, Ph.D. “Retrovirus.” National Human Genome Research Institute. (Accessed August 17, 2021). https://www.genome.gov/genetics-glossary/Retrovirus
“What is coronavirus and Covid-19? An explainer.” CNN Health. March 31, 2020. https://www.cnn.com/2020/03/31/health/what-is-coronavirus-covid-19-wellness/index.html
Aaron Kandola. “What are the different types of coronavirus?” Medical News Today. September 27, 2020. https://www.medicalnewstoday.com/articles/types-of-coronavirus
Institute for Quality and Efficiency in Health Care (QWiG). “The innate and adaptive immune systems.” Informedhealth.org. Updated July 30, 2020. https://www.informedhealth.org/the-innate-and-adaptive-immune-systems.html
Dr. Dinusha. “Difference Between Antigen and Antibody.” Difference Between.com. September 29, 2011. https://www.differencebetween.com/difference-between-antigen-and-vs-antibody/
Dr. Guru. “Difference Between T Lymphocytes and B Lymphocytes.” Difference Between.com. December 23, 2010. https://www.differencebetween.com/difference-between-t-lymphocytes-and-b-lymphocytes/
Eliott C. McLaughlin. “The difference between elimination, eradication and herd immunity – what it means for Covid-19.” CNN health. May 12, 2021. https://www.cnn.com/2021/05/12/health/history-pandemics-eradication-elimination/index.html
Selected Sources and Further Reading (Vaccines)
Robyn Correll, MPH. “How do Vaccines Work, Exactly?” verywellhealth. March 4, 2020. https://www.verywellhealth.com/how-do-vaccines-work-4153906
“The immune System-The Body’s Defense Against Infection.” Understanding How Vaccines Work | CDC. (Accessed May 8, 2020). https://www.cdc.gov/vaccines/hcp/conversations/understanding-vacc-work.html
“The different types of COVID-19 vaccines.” World Health Organization. (Accessed August 18, 2021). https://www.who.int/news-room/feature-stories/detail/the-race-for-a-covid-19-vaccine-explained
“Development of New Vaccines.” Vaccines & Immunizations, CDC. (Accessed May 8, 2020). https://www.cdc.gov/vaccines/basics/test-approve.html
Fran Kritz. “What’s the Difference Between Emergency Use Authorization and Approval?” verywell health. December 18, 2020. https://www.verywellhealth.com/emergency-use-authorization-vs-approval-5092864
“Vaccine Adverse Event Reporting System (VAERS).” U.S. Department of Health and Human Services (HHS). (Accessed May 13, 2021). https://vaers.hhs.gov/
“Diseases & the Vaccines that Prevent Them.” Vaccines and Preventable Diseases. Centers for Disease Control and Prevention (CDC). (Accessed August 7, 2021). https://www.cdc.gov/vaccines/vpd/index.html
“Vaccine History: Developments by Year.” Children’s Hospital of Philadelphia. (Accessed August 9, 2021). https://www.chop.edu/centers-programs/vaccine-education-center/vaccine-history/developments-by-year
Selected Sources and Further Reading (Smallpox)
Jesse Greenspan. “The Rise and Fall of Smallpox.” History. May 7, 2015. Updated May 15, 2020. https://www.history.com/news/the-rise-and-fall-of-smallpox
Stefan Riedel, MD., PhD. “Edward Jenner and the history of smallpox and vaccination.” Baylor University Medical Center Proceedings. January 2005. 18(1). Pages 21-25. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1200696/
Gilliam Brockell. “Smallpox ‘virus squads’ and the mandatory vaccinations upheld by the Supreme Court.” MSN, The Washington Post. April 1, 2021. https://www.msn.com/en-us/news/us/smallpox-virus-squads-and-mandatory-vaccinations-upheld-by-the-supreme-court/ar-BB1fcNjy
“Smallpox.” Vaccines and Preventable Diseases. Center of Disease Control and Prevention. (Accessed August 7, 2021). https://www.cdc.gov/vaccines/vpd/smallpox/index.html
Michael Willrich. POX, An American History. Penguin Random House. March 27, 2012. https://www.penguinrandomhouse.com/books/298913/pox-by-michael-willrich/
Selected Sources and Further Reading (Polio)
Mary Anne Dunkin. “Polio Vaccine (IPV).” webMD. June 3, 2020. https://www.webmd.com/children/vaccines/polio-vaccine-ipv
“Polio.” Vaccines and Preventable Diseases. Center of Disease Control and Prevention. (Accessed August 7, 2021). https://www.cdc.gov/vaccines/vpd/polio/index.html
Selected Sources and Further Reading (Childhood Diseases)
Brian Mastroianni. “Measles in America: What Life Was Like Before and After the Vaccine.” Healthline. March 6, 2019. https://www.healthline.com/health-news/life-before-and-after-the-measles-vaccine#Whatisthemeasles
“Measles.” Vaccines and Preventable Diseases. Center of Disease Control and Prevention. (Accessed August 7, 2021). https://www.cdc.gov/vaccines/vpd/measles/index.html
“Rubella.” Vaccines and Preventable Diseases. Center of Disease Control and Prevention. (Accessed August 7, 2021). https://www.cdc.gov/vaccines/vpd/rubella/index.html
“Mumps.” Vaccines and Preventable Diseases. Center of Disease Control and Prevention. (Accessed August 7, 2021). https://www.cdc.gov/vaccines/vpd/mumps/index.html
“Chickenpox (Varicella).” Vaccines and Preventable Diseases. Center of Disease Control and Prevention. (Accessed August 7, 2021). https://www.cdc.gov/vaccines/vpd/varicella/index.html
Technical Reading
Edward Jenner. “An inquiry into the causes and effects of the variolae vaccinae: a disease discovered in some of the western counties of England, particularly Gloucestershire, and known by the name of the cow pox.” Springfield [Mass.]: Re-printed for Dr. Samuel Cooley, by Ashley & Brewer, 1802. https://collections.nlm.nih.gov/catalog/nlm:nlmuid-2559001R-bk & https://collections.nlm.nih.gov/ext/mhl/2559001R/PDF/2559001R.pdf
Walter R. Dowdle. “The Principles of Disease Elimination and Eradication.” CDC, Morbidity and Mortality Weekly Report (MMWR). 48(SU01);23-7. December 31, 1999. https://www.cdc.gov/mmwr/preview/mmwrhtml/su48a7.htm