Question: What is immune escape?
Answer: Immune escape (aka viral escape and antigen escape) is the ability of a virus to elude an individual’s immune response. In the context of new SARS-CoV-2 strains, the term has come to prominence as scientists examine whether the new strains exhibit immune escape in terms of vaccine resistance. In good news, initial data show that “existing vaccines should work against new coronavirus variants—for now.”
Unlike drug resistance, which is common, vaccine resistance is rare (Figure 1). This paper published in 2017, Why does drug resistance readily evolve but vaccine resistance does not?, offers a useful hypothesis to explain this dichotomy: 1) Vaccines tend to work to prevent disease whereas drugs tend to work to treat disease (i.e. vaccines generally give fewer opportunities for viral replication and spread to others); 2) Vaccines tend to induce immune responses against multiple targets on the virus whereas drugs tend to target very few (i.e. unlike drugs, vaccines generally require immune escape from multiple targets). A more recent paper from these same authors published in November in PLoS Biology describes one more feature of a vaccine that limits resistance: generally, the immune response elicited by the vaccine protects against all circulating types of the virus. What we know of the vaccines we currently have against COVID is that they do meet all three criteria– 1) they prevent disease (though we still don’t know whether they prevent infection); they induce a complex immune response; and 3) they work against all currently circulating variants.
If you’d like to read more, this Nature article published last week is an informative read as is this National Geographic article published earlier today.
*Update: for response to Geert Vanden Bossche’s letter, see Q&A of 3/17.
Figure 1. Time to first detection of human pathogens resistant to vaccines and antimicrobial drugs (from Kennedy DA, Read AF. Why does drug resistance readily evolve but vaccine resistance does not?. Proc Biol Sci. 2017;284(1851):20162562)
