Hepatitis B (Hep B) vaccine given to Hep B infected person isn’t likely to work. My answer explains why. In the context of this question, we need to consider two types of vaccines,

  • Prophylactic: vaccine given to an uninfected person. Goal of prophylactic vaccines is to prevent disease.
  • Therapeutic: vaccine given to an infected person. Goal of therapeutic vaccines is to treat ongoing disease.

if Hepatitis B vaccine were given to a Hepatitis B infected person‘ is an example of a therapeutic, not prophylactic, vaccine.

Prophylactic, therapeutic. What’s the difference and why should we care?
Big difference. As the name suggests, Hepatitis B (Hep B) infects liver cells (hepatocytes) and lives inside them.

What a Hep B vaccine needs to do in an uninfected person, i.e., prophylactic:

  • Hep B virus needs to infect hepatocytes to survive after entering an uninfected person.
  • Goal of prophylactic Hep B vaccine is to generate sufficient amount of anti-Hep B antibodies to neutralize the virus, stopping it in its tracks even before it gets a chance to reach the liver and infect hepatocytes (see figure below).

What a Hep B vaccine needs to do in an infected person, i.e., therapeutic, is totally different:

  • Hep B has already invaded and resides within hepatocytes.
  • Anti-Hep B antibodies are of little use in this situation since typically antibodies can’t/don’t penetrate inside cells.
  • Need a different type of immune response, namely, anti-Hep B cytotoxic CD8 T cells to selectively kill Hep B-infected hepatocytes.
  • Thus, a therapeutic Hep B vaccine needs to induce  anti-Hep B CD8 cytotoxic T cells, not antibodies.

Most approved infectious disease vaccines today including the prophylactic Hep B vaccine induce antibody responses.

  • Such vaccines are poor inducers of CD8 cytotoxic T cell immune responses.
  • That’s not all. Ongoing Hep B infection is by no means benign, especially to the person’s immune system.
  • For one, it appears to blunt the capacity of helper CD4 T cells (2, 3, 4, 5; see figure below from 5).
  • In turn, these cells are critical in helping anti-Hep B CD8 cytotoxic T cells acquire the capacity to become killer cells.
  • So Hep B infection impairs helper CD4 T cells resulting in ineffective cytotoxic CD8 T cells (6).

Simply put, effective prophylactic vaccines are simpler to design compared to therapeutic ones, especially for Hep B. At the present moment, approved Hep B vaccines are prophylactic, not therapeutic.

And what happens in case of polio virus or HPV?‘. Similar principle applies to viruses like polio or HPV though the cells they infect are different, motor neurons and keratinocytes, respectively. A prophylactic vaccine that induces antibodies is effective in blocking virus from infecting an uninfected person while CD8 cytotoxic T cells are needed to kill virus-infected cells in infected persons so a different kind of therapeutic vaccine is needed.

And what to do if a person did’t receive any vaccine in childhood? Also if the person at 25 years of age never experienced any serious infectious disease? What are vaccines the person should take now?
Each country has different vaccination schedules since prevalence of different infectious diseases differs from country to country. If the person lives in India, the Government of India provides a detailed guideline that answers these questions (7),

If the person lives in the US, the CDC (Centers for Disease Control) provides a detailed guideline that answers these questions  (8).

This person should consult a local GP (General Practitioner) near their residence to guide them in working out their immunization schedule and who should supervise their catch-up vaccinations.


  1. Michel, M-L., and P. Tiollais. “Hepatitis B vaccines: protective efficacy and therapeutic potential.” Pathologie Biologie 58.4 (2010): 288-295.
  2. Ferrari, C. A. R. L. O., et al. “Cellular immune response to hepatitis B virus-encoded antigens in acute and chronic hepatitis B virus infection.” The Journal of Immunology 145.10 (1990): 3442-3449.
  3. Wang, Fu-Sheng, and Zheng Zhang. “Host immunity influences disease progression and antiviral efficacy in humans infected with hepatitis B virus.” (2009): 499-512.
  4. Bauer, Tanja, Martin Sprinzl, and Ulrike Protzer. “Immune control of hepatitis B virus.” Digestive Diseases 29.4 (2011): 423-433.
  5. Schmidt, Julia, Hubert E. Blum, and Robert Thimme. “T-cell responses in hepatitis B and C virus infection: similarities and differences.” Emerging Microbes & Infections 2.3 (2013): e15. Page on nature.com
  6. Rehermann, Barbara, et al. “The cytotoxic T lymphocyte response to multiple hepatitis B virus polymerase epitopes during and after acute viral hepatitis.” The Journal of experimental medicine 181.3 (1995): 1047-1058. Page on rupress.org
  7. Page on ncdc.gov.in
  8. Page on cdc.gov