Dear @Monkeiiboy,
Thank you for sharing your story and highlighting an important issue: where the scientific/academic meet the reality of human relationships.
First of all, good on you for being informed and empowered enough to provide that information to potential partners. I’m super impressed and can see how that can be quite a big responsibility to take.
This is my impression too, given that this is generally the advice given to relationships where people are trying for a pregnancy and the male is HBV-positive (though vaginal transmission in general seems to be lower than anal transmission).
There are multiple aspects that may relieve your conscience:
- Being a bottom, you are less likely to transmit compared to being a top.
- Scientists and clinicians will generally be quite conservative in these cases. This makes sense legally and ethically speaking; there is power in words when you are a trusted expert, and one doesn’t want to wield them incorrectly.
- Just to provide some context of transmission risk: see figure 2 in this WHO report https://apps.who.int/iris/bitstream/handle/10665/333391/9789240002708-eng.pdf. It shows that in high fluid exchange setting (birth of a child), maternal virus levels less than 20000 do not result in a chronic infection in newborns, who are very highly susceptible to chronic infection. Of course, it needs to be added that the newborns are vaccinated straight away and given HBIg (this prevents infection in 75-90% of cases, without antivirals).
- Another study (https://gut.bmj.com/content/68/2/313) has looked at the minimum infectious dose in the setting of blood transfusion from people who are have undetected HBV DNA (<10IU/mL). They found that the minimum infectious dose could be between 100-16 copies (16 copies = 3IU) in “susceptible recipients non-immune to HBV”. This means you’d need on the order of a third of a mL of fluid transfer directly administered to the blood, probably unlikely with micro-tears associated with sex (happy to be corrected on this though). A comment to this paper also talks about high variability in the infectiousness dose - New minimum infectious level of hepatitis B virus proposed and continued testing for HBsAg questioned - McCullough - Annals of Blood.
- Adults exposed to HBV are highly likely to clear it (90%, even without vaccination) and not have a chronic infection, though there is a risk of acute hepatitis.
In the end, it really depends on how you define “safe”, which I suspect this is different for everyone.
Unfortunately, I don’t think there are clear answers to your questions. It is true there is not enough evidence provided for many doctors or scientists to be comfortable with saying you’re completely safe.
I would be keen to hear perspectives from @HealthExperts here.
Hope this helps a bit,
Thomas