Thread by @GertrudRey

Last month’s 🧵 provided an overview of various traditional #vaccine technologies. The current 🧵highlights more recent advances in the field.

Also at virology blog. 1/

virology.ws/2025/11/06/vac…

Genetic vaccines introduce nucleic acids (DNA and/or RNA) into a recipient’s cells. Once inside the cells, these genetic instructions are used by the cell’s machinery to produce a specific protein. 2/

The protein is usually an immunodominant antigen derived from a pathogen, which triggers an immune response specifically targeted at that pathogen. Genetic vaccines include viral vector vaccines, mRNA vaccines, and DNA vaccines, all of which are discussed in more detail below. 3/

Viruses enter cells by attaching to host cell receptors and releasing their genome into the cell. Viral vector vaccines are based on this principle and consist of a virus – typically an adenovirus – with an inserted gene that encodes an antigen of choice. 4/

Several genes native to the vector virus are usually deleted to render it non-infectious and to make space for the inserted antigen gene. Once injected into a person, the vaccine vector should enter cells, and its nucleic acid will serve as a template from which the antigen... 5/

...protein will be produced. The antigen will then prime the immune system to recognize the pathogen from which the antigen originated. When the individual is infected with the pathogen later, it will be recognized by the immune response. 6/

Several COVID-19 viral vector vaccines encoding the antigenic SARS-CoV-2 spike protein were developed during the pandemic; however, their use in the USA was discontinued because they are less effective than mRNA vaccines.* 7/

*During the pandemic I discussed at least two COVID-19 viral vector vaccines developed separately by AstraZeneca and Johnson & Johnson.

A drawback of viral vector vaccines is that unfortunately many people have pre-existing immunity to the vector viruses. 8/

In this case, the antibodies to the vector itself neutralize it before it can deliver its genetic payload, thus reducing vaccine efficacy. 9/

Nevertheless, two licensed Ebola virus vaccines consisting of viral vectors and encoding the Ebola virus (previously known as “Zaire ebolavirus”) glycoprotein are currently in use, and they are more than 97% effective at preventing Ebola disease. 10/

mRNA vaccines gained a lot of attention during the COVID-19 pandemic, but their history is long and complex. These vaccines consist of an mRNA that is encapsulated in a lipid nanoparticle, which protects the mRNA from degradation and ensures proper delivery into cells. 11/

The mRNA encodes an antigen, which in the case of the COVID-19 vaccines is the SARS-CoV-2 spike protein. After the vaccine is injected into a recipient, the mRNA enters cells, where host proteins translate it into the SARS-CoV-2 spike protein, which then promotes an... 12/