Vaccines

What is the best defense against viruses?

Vaccination

• Induce the host immune response to prevent virus disease

• Slows the chain of transmission, prevent large outbreaks

Smallpox

• Caused by the Variola virus

• Symptoms: fever and vomiting followed by skin rash (rash turned into fluid filled bumps with dent in the center, 1/3 of patients would end up blind)

• Spread through close contact or contaminated objects

• Earliest evidence of disease in 3rd century from Egyptian mummies

• Caused periodic outbreaks throughout history

• 18th century Europe estimates 400,000 were dying each year

• Estimated to have killed 300 million people in the 20th century

• Typical case fatal rate of 30%

Variolation

• Measures to control infectious diseases started long before infectious diseases were identified

• Developed in China around 1000 BC

• Induced immunity by purposefully infecting a human with the less virulent smallpox Variola isolate, which usually caused only a mild clinical disease

• Find someone with a mild case of smallpox, scrape the scabs and pus from the pox, grind the matieral and this was either blown up the nose or rubbed into the small scratches in the skin

• Become common in China and Africa

1721 - Lady Mary Wortley Montagu

• Lost her brother to smallpox and had severe facial scars from her pox infection

• While traveling in Turkey witnessed variolation and had her 5 yo son inoculated

• Brought him and daughter to England and had her daughter inoculated at the royal court

• A group of prisoners were inoculated and then exposed to smallpox - they survivied and Europe began variolation as a standard practice

• Produces a characteristic pox lesion on the hand or arm

• It is possible for a human to die from variolation (1 to 2% of those variolated died as compared to 30% who died when they were exposed to the disease)

1721 - Onesimus

• African slave forced to come to the US in the late 1600s

• Was purchased for a Puritan church minister named Cotton Mather in 1706 in Boston

• He told Mather about the centuries old tradition of inoculation practiced in Africa

• When a smallpox epidemic hit Boston in 1721, Mather convinced Dr. Zabdiel Boylston to experiment with the procedure, and over 240 people were inoculated (6 died, or 1 in 40; 1 in 7 of the non-variolated Bostonians died)

• The practice was also used to inoculate American soldiers during the Revolutionary War

Other famous people who supported variolation

• George Washington was scarred from smallpox, but ensured his wife was variolated to prevent her from getting sick

• 1775 George Washington ordered the whole Continental Army to be variolated

• James Madison had his whole family variolated during a smallpox outbreak

• Benjamin Franklin did not have his family variolated, but after his 4 yo son died from smallpox, he became an advocate

Vaccination - Dairymaids

• Some people observed dairymaids in close contact with cows with cowpox would get lesions on their hands, but survive Smallpox outbreaks

• Vacca means cow

• Rather than using a Smallpox lesion to variolate, they used a cowpox lesion to “vaccinate”

Benjamin Jetsy and Edward Jenner

• Jetsy (a farmer) inoculated his wife and 2 sons with cowpox virus from the udder of an infected cow in attempt to control smallpox (1774; on of ½ dozen persons who’s work pre-dated Jenner’s)

• Jenner recognized that dairymaids infected with cowpox virus were resistant to infection by smallpox virus

• 14th of May 1796, used cowpox-infected scab material obtained from a milkmaid to vaccinate 8 yo Jamers Phipps (son of his gardener) → then oxposed Phipps to people acutely ill with smallpox, which Phipps failed to contract the virus

• He repeated the experiment on other children, including his own son (concluded that vaccinatation provedied immunity to smallpox without the risks of variolation)

Jenner’s findings

• Jenner’s findings were published in 1798 and was given the title of father of vaccination

• In the 1800s, cowpox virus used for smallpox vaccination was propagated by infecting different farm animals 

• Somehow, cowpox changed to become vaccinia virus

• Vaccinia virus is in the poxviridae family, but is genetically unrelated to cowpox and smallpox viruses, but still protects human against smallpox virus infection (most similar to a horse pox virus)

Vaccination and Eradication

• Smallpox was the firsu human disease eliminated (eradication program launched in 1967; eliminated in 1978)

• Eradication was possible becuase of vaccination (smallpox virus was only found in humans, ring vaccination strategy at the end, identify a positive host and vaccinate everyone around them)

Vaccines are now common place

• Children, adults, pets, livestock and even wild animals are routinely vaccinated

• Most doctors in the US have never seen cases of measles, mumps, polio, etc.

• Unfortunately, some countries still do not have access to all of the vaccines (150,000 children die each year from Measles virus)

How do vaccines work?

• Vaccines induce a critical level of immunity in individuals that will prevent them from getting sick (great vaccines prevent them from getting infected)

• When enough people in a community have the critical level of immunity, the infectious agent will be unable to spread (herd immunity)

• Each virus has a different threshold to prevent its spread (smallpox → 80-85%; Measles → 93-95%)

• Vaccines aren’t perfect and not everyone will be protected, everyone needs to get vaccinated to protect those who can’t receive the vaccine

Complacency is Dangerous

• Most people who grew up in the US in the last 40 years have never seen anyone get the measles, mumps, rubella, polio, diphetheria, tetanus, etc.

• People think that just “itchy rashes” and forget that children would die before vaccines

• Reasons people use for not vaccinating: polio is long gone, I never get the flu, Measles is just a little rash, Kids would get better immunity if they are naturally infected, Shots are full of chemicals, Vaccines cause autism or multiple sclerosis, My friend got the flue from the flu shot

Active Vaccines

Vaccinate with a modified form of the pathogen or part of a pathogen to induce the recipient to make antibodies (long term protection, induce a memory response)

Passive Vaccines

give the product of an immune response (antibodies or immune cells) to a recipient 

• short term protection

• no memory response

• maternal protection

Regeneron and other SARS-CoV-2 antibodies

• Clone out of the coding region to antibodies to SARS-CoV-2 spike from a mouse or human patients

• (if from a mouse - clone them into a human IgG1 construct)

• Produce the antibodies (tobacco plants, tissue culture)

• Very effective if given early in infection for COVID (Ebola monoclonals did not show efficacy)

Lassa Fever Passive Therapy

• Jordi Casals infected himself with Lassa virus at Yale in 1969

• Took blood from a Lassa survivor (nurse Penny PInneo) and transfused Casals to provide a passive vaccine

What makes a good vaccine?

• Induce an appropriate immune response (Th1 vs Th2 → T Cell vs B Cell balance)

• Vaccinated individuals must be protected against disease (not necessarily prevent them from getting infected) → GREAT vaccines prevent infection (like HPV vaccine)

• Just getting a response, (you make antibodies after the vaccination) does not mean you are protected → neutralizing antibodies are needed for most viral vacciens, prevent pathogen from causing symptoms

• Safe: no disease or side effects

• Long-lasting protection

• Low cost (<$1 according to the WHO)

Inactivated Vaccines

• Chemically inactivate the virus (Formalin, Beta-propriolactone, Nonionic detergents)

• Infectivity is eliminated

• Antigenicity is not compromised

• “Looks just like the real thing”

Poliomyelitis Quote

“A common, acute viral disease characterized clinically by a brief febrile illness with soure throat, headache and vomiting, and often with stiffness of the neck and back. In many cases a lower neuron paralysis develops in the early days of the illness.”

Poliomyelitis Details

• Polio: (+) ssRNA virus, naked icosahedral capsid

• Spread through fecal-oral route

• Causes mostly asymptomatic infection - people do not notice they are infected, yet can spread the virus

• 1:200 cases the virus gets into the nervous system and can cause paralysis

• Poor sanitation before 1900s meant people were constantly exposed to polio, starting from an early age and very few cases of paralytic polio were seen

• Better sanitation meant kids could not be exposed to polio until later in life, and age seems to increase the rates of paralytic polio

• Parents and children were scared of polio in the 1940s-50s

Inactivated poliovirus vaccine, IPV

• Jonas Salk developed first polio vaccine

• Poliovirus treated with formalin to destroy infectivity

• 1954: National Foundation for Infantile Paralysis sponsored a clinical trial of Jonas Salk’s IPV (1,800,000 children; 1955 results announced >50% protection and was licensed on the same day)

Cutter Incident (1955)

• Improperly prepared vaccine (120,000 doses contained “live” polio virus)

• Virus not inactivated

• 40,000 developed abortive poliomyelitis

• 56 paralyzed

• Investigation revealed that vaccine was not made and tested properly

• All companies making the vaccine reported difficulties in completely inactivating the virus

Infleunza Virus

• Flue causes 3000-50,000 deaths in the US each year 

• A: can have pandemic potential - infects wild birds and many other animals

• B: only transmitted by humans

Influenza Virus Vaccine

• As a segmented RNA virus, influenza can reassort and drift year-to-year

• Because it takes time to get the vaccine produced, they need to choose the strains to use in the vaccine months before the virus will start spreading in the US

• They make re-assorted viruses with the HA and NA segments of the chosen strains

Flue Vaccine Method

• Annual vaccine is made in embryonated chicken eggs and is formalin inactivated, and detergent and/or chemically disrupted

• 75-100 milion doses of flu vaccine are made each year

• Depending on the year, the vaccine is about 60% effective in healthy people 1-65 yo (makes antibodies against HA)

• New vaccine is made in tissue culture cells so people do not need to worry about egg allergies

Subunit Vaccines

• Break virus into components

• Clone specific viral proteins and express in bacteria, yeast, insect cells, or cell culture, purify proteins and use for vaccine

• Antigens usually capsids or membrane proteins

Hepatitis B Vaccines

• Hep B antigens produced in yeast

• Assemble into particles - produce a great immune response

HPV Vaccines

• Gardasil (Merck): types 6, 11, 16, 18 produced in S. cerevisiae

• Gardasil-9 (Merck): types 6, 11, 16, 18, 31, 33, 45, 52, 58

• Cervarix (GlaxoSmithKline): types 16, 18 produced in insect cells

Inacivted → viral like particles

Subunit Vaccine Pros and Cons

• Advantages of a modern subunit vaccine: recombinant DNA technology, no viral genomes or infectious virus

• Disadvantages: expensive, injected, poor antigenicity, requires multiple doses

Common Problem of Inactivated and Subunit Vaccines

• Viral proteins don’t replicate or infect

• Don’t send out ‘danger signal’ to the immune response

• Pure proteins often require adjuvant to mimic inflammatory effects of infection

Replication Competent, Attenuated Vaccines

• Viral replication occurs, stimulates immune response

• Infection induces mild or inapparent disease

How are attenuated viruses made?

Serially passage virus

• Non-human cell - virus changes to grow well in different types of species

• Altered temperature: virus changes to grow well in temperature not found at normal site of infection

Example of an Attenuated Vaccine

Sabin Oral Poliovirus Vaccine (OPV)

• Sequenced and found to have very few changes

• Within 2 days, reverts to wt polio and then shed through the environment

Reported Cases of Paralytic Poliomyelitis, US, 1961-2003

• Polio cases were all vaccine related because we were using OPV which would revert and get spread into the environment

• Switched to IPV in 2000 (no wild polio originating in US since 1979 (only travelers cases) 

• No vaccine associated polio since 2000 - until 2022

Potential Universal Flu Vaccine

• Find an antigen that can inhibit all influenza viruses

• HA stem antibodies

• M2 as an antigen (ion channel)

Vaccines help your immune system have a head start

COVID Vaccine

• Present the spike protein to your immune system

• Produce antibodies to block SARS-CoV-2

• Neutralizing antibody attaches to spike protein and prevents binding to ACE2 receptor

Vesicular Stomatitis Virus Vector

• Use recombinant DNA technology

• VSV is a disease of cattle, doesn’t cause disease in humans, but replicates in human cells

• Remove Glycoprotein gene (gene in viral membrane) and replace with other virus glycoprotein gene like Ebola

• Virus replicates using Ebola entry pathways and immune response will be directed against it producing neutralizing antibodies

Viral Disease Eradication

• What are the requirements to eradicate a viral disease?

  • Replication only occurs in one host

  • Vaccination induces lifelong immunity

• Viral diseases that are species specific (Smallpox, Polio, Measles, Rubella, Rinderpest → cattle and even-toed ungulates)