Hi
Is it true that vaccine escape mutants don’t spread very well? Is this because of lower replication? I am wondering if the baby infected perinatally with the vaccine escape mutant e.g. pre-S gene will transmit the virus to vaccinated people easily in the immune tolerant phase. Can I please ask experts to advise?
Thanks
Dear @anonymous75,
This is a great question but the answer is not straight forward.
We know that HBV vaccine escape mutants can be transmitted between the mother and her baby, eventually developing break-through disease even with the birth dose vaccination in place, but these cases are relatively rare. Different escape mutants will have different levels of replication competency. The depends on when they emerge during the course of disease and the level of immune exhaustion against HBV which has occurred and how the mutation actually affects the release of new virus into the blood.
While there are well documented cases of HBV birth dose vaccine failure in newborns, there has never been a documented case of transmission of a vaccine escape mutant from an infected child (or adult) to someone who has already been vaccinated.
It is important to remember that ~80% of people who get infected with HBV self-resolve their own infection to a point of functional cure (complete immune control). These people are never infectious and almost never develop disease from the initial infection (unless they become severely immunosuppressed). This immune control process is the same as for other viruses such as HSV-1 (cold sores) or varicella zoster (chicken pox) which infect almost everyone on the planet but remain latent (under immune control). Like HBV, these viruses become permanently resident in the body but do not replicate or cause disease.
Unlike peri-natal HBV transmission (where mutants are more likely to be transmitted and establish themselves in the liver), classical transmission can only occur when infected blood is transmitted through a cut in the skin or from a needle. In these cases the HBV innoculum is mostly wild type (or very close to wild type). This is why prophylactic vaccination (prior to HBV exposure) using vaccines containing wild type HBV antigens is so effecting in preventing the development of disease and transmission of infection in the vaccinated individual.
Hi @anonymous75,
Just adding on to what @availlant has mentioned here (all of which is accurate), the number of reported vaccine escape mutants is very low and has not affected the general public health control of Hep B through vaccination at any practical level.
Thomas