Types of Vaccines

While all vaccines activate our immune system by stimulating the creation of memory cells, there are several different ways to accomplish this goal.  In addition, this is an area of very active research and as we can see now with the COVID-19 vaccines, there are new methods of accomplishing this goal.   Here is a brief explanation of the different  types of vaccines.

Older Technologies

These types of vaccines have been used over the last 100 years or more. Indeed, ancient Chinese methods called variolation are essentially a precursor  of these 3 techniques.(Samples from smallpox pustules were ground up, powdered and inserted via the nose to induce a mild version of the disease and induce immunity in the patient) 

1. Inactivated Vaccines

The pathogen is killed using heat or some chemical.  They don't trigger as strong an immune response as some other types of vaccines and sometimes need booster shots ( a 2nd dose). 

Examples: Flu shots, Rabies. 

2. Live-attenuated Vaccines

Attenuated means weakened. These vaccines are made by growing a weakened version of the pathogen that  has trouble replicating itself in a human body.  Because these are the actual pathogen, they induce a strong immune response.  There is the risk that the virus could revert to a more potent form, but this is  minimized by the fact that they don't replicate in the body. 

Examples: Measles, mumps, rubella, chickenpox 

3. Subunit Vaccines

The vaccine is simply a specific part of the pathogen. For example, just one specific protein from a virus or bacteria is grown up in large quantities and injected.   The immune response will be targeted at that one part of the pathogen. They don't always induce as strong an immune response and may need boosters or adjuvants (an addition to the vaccine that aggravates the immune system so it responds more strongly)  One advantage is that they can be given to people who have weakened immune systems and other health problems

Examples: Hepatitis B, HPV, whooping cough, 

Newer Technologies 

4. Viral Vector Vaccines 

Since the Ebola outbreak of 2014-2016 scientist have been working to create a ''plug and play'' system for vaccine development. They knew that we would be facing new viral threats and we would have to respond quickly .(And they were right!)  Viral vectored vaccines were one of these solutions. They work like this:

• • • • Take a harmless virus ( Adenoviruses cause cold like symptoms)= the vector (something that transmits something)
      • Take a gene for some harmless part of your pathogen ( like the spike protein gene) 
      • Insert it into your vector virus.
      • Grow up your vector virus 
      • Inject that into the patient.
      • The vector virus infects human cells and forces them to make copies of the protein from the pathogen.
      • Your immune system recognizes this as ''foreign'' and starts the activation process that leads to memory cells. 

The advantage is that once you have the vector system working well, the scientists ''only'' have to insert the DNAsequence for a part of the pathogen. For example, Chinese scientists published the entire DNA sequence for SARS COV2 in January of 2020 and within 10 days scientist had begun working on inserting the spike protein gene into the Adenovirus and started human trials by April.

Examples: Zika, Eboloa, Covid-19

5. mRNA Vaccines

One of the largest problems with the traditional vaccines is that they take a long time to develop. In the era of newly emerging viruses, we  need a faster turn around time. For this reason, for decades  there has been a great interest in mRNA vaccines as well as research.   Researchers had done a lot of the basic background research on the system, and the COVID-19 pandemic was a call to arms!

Here's how they work:

• • • • Sequence the genome of the pathogen (SARS-COV2 in this case)
      • Find the gene for a protein that will cause a strong immune response - luckily coronaviruses are well studied and scientists already knew to use the spike protein
      • Make the mRNA for that protein
      • Wrap the mRNA in an lipid bubble
      • Inject this into the patient
      • The lipid fuses with cell membranes and the mRNA is in the cell
      • The mRNA is read by ribosomes which make the spike protein
      • The spike protein is put into the cell's membrane
      • The immune system recognizes this as ''foreign''  and the process starts that leads to memory cell development 
      • (ps. mRNA doesn't last too long so it  breaks down and is cleaned up- in short order!)

The advantage is that this is a very simple system with few components. That makes it fast and cheaper to develop. So for example, if their are new variants of the SARS COV2 they can quickly make a new vaccine to target that.  The downside is that because mRNA is so fragile, they need to be kept at very cold temperatures when stored.  But research is working on solving that problem

Examples: COVID-19 

This video has some nice visuals and summary of the different types of vaccines. 

Now take a mini-quiz on this topic to make sure you've done the reading and are prepared for class.