Is it infectious

I have read that even with treatment antiviral medication, loss of e antigen, and undetectable virus in the blood, that one is still infectious due to virus levels in other body fluids. I have heard for years that in that particular state (undetectable, e antigen loss), one is not infectious. I am not sure what to make of that?

My second question is, is PrEP for HIV effective in preventing acquisition of HBV? There has been some research indicating it is. There is limited additional research on this that I have seen. IIf so, there is no educational efforts to promote PrEP and HBV vaccinations.

Also, I do not feel like PrEP clinics and LGBTQIA clinics are emphasizing any efforts to vaccinate people for HBV as standard protocol when seeing patients for sexual health and/or PrEP. Anyone have more info on this?

Maybe I am reading the wrong articles or having experiences that are not the majority.

Hello @MeDNP
I understand your confusion too.
I Think what they mean by us, not being infectious, is our chances of passing on the disease is very low, and they call that not infectious. Confusing, yes. I’m glad that you are being aware that you still are.
HBV isn’t discussed among many communities. I don’t understand why everyone isn’t screen for HBV. I even asked my doctor why he doesn’t screen his patients for HBV, and he said, none of my patients would have it! And I thought how would you know if you don’t test them. That would bring the death rate down quite a lot.
Maybe others can help with your questions.

Dear @MeDNP,

Thanks for your questions. Scientifically speaking, there is still a (very low) chance of transmission if you are on treatment and your HBV DNA levels are undetectable. This is because there is a small chance that there is a little bit of virus that is under the detection limit of our tests. This is only really likely if you transfer a LARGE amount of bodily fluid to someone (e.g., blood transfusion).

Regarding PrEP, there are studies that have shown that it is effective in prevention of HBV (Effect of tenofovir-based HIV pre-exposure prophylaxis against HBV infection in men who have sex with men - PMC). There is a push here in Australia to include information about Hepatitis B in sexual health clinics, but HIV is definitely still the major focus.


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Hi Thomas,

Are there any percentages or statistics available regarding transmission if your viral load is undetectable? How low is “very low”? Why is it that with HIV “undetectable = untransmissible” but this can’t be said with hepatitis B?

Dear @Barry,

Great questions and they are ones that the field is trying to find out at the moment!

For the answer to these questions, it is not ethical to do actual experiments. Instead we need to review events that have happened in real life circumstances; these are less controlled so that we can’t be as certain about specific numbers, but it’s the closest we can get.

Most recently there has been data on blood transfusions from HBcAb-positive donors who were HBsAg-negative and with undetectable (less than 3.4 IU/mL) HBV DNA levels (Multiple HBV transfusion transmissions from undetected occult infections: revising the minimal infectious dose | Gut). They found that there was a 30% chance of infection in recipients after transfer of 20-200mL of donor material (red blood cells or plasma). From this, they calculated that the minimum infectious dose is 100 to 16 copies of HBV DNA - that is you need to put 16-100 viral copies into someone to infect them. This is the reason we can’t say undetectable = untransmissible. However, in everyday circumstances, you are not taking 200mL of your own serum and directly injecting it into someone else.

In another example, there has not been a reported circumstance where there has been a mother to child transmission (given post-birth HBIG and vaccination) where the mother’s viral load is below 160,000 IU/mL (Figure 2 from a WHO report - Prevention of mother-to-child transmission of hepatitis B virus: Guidelines on antiviral prophylaxis in pregnancy). So even in the very messy situation of birth where there is a lot of fluid exchange, moderate levels of viral load, and a highly susceptible person involved (the newborn), the infection does not necessarily take hold.

Like I said, there is not necessarily firm statistics on the risk, but I hope this gives you some perspective about what is required for transmission and infection.


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Thanks, Thomas for that information. How would you assess the risk of transmission in the case of deep kissing? Can saliva be a source of transmission of hepatitis B?

Thomas, have you heard about a study (maybe not a study) that looked at the presence of hep b virus in various body fluids for those on treatment and determined that virus was present in different body fluids to varying degrees even with undetectable levels in blood? Does that say much regarding infectiousness of the virus?

Hi @MeDNP and @Barry ,

Great questions. There have been studies of HBV DNA being detected in other bodily fluids (e.g., High levels of hepatitis B virus DNA in body fluids from chronic carriers - PubMed,, and but I’m not sure about on treatment. However, the studies that have been done show that the viral load in semen and saliva are hundreds to thousands times lower than it is in the blood, so the risk of transmission is lower compared to blood-to-blood contact.

Hope this helps,