The main news is that in PARTNER so far there have been no transmissions within couples from a
partner with an undetectable viral load, in what was estimated as 16,400 occasions
of sex in the gay men and 28,000 in the heterosexuals.
some of the HIV-negative partners became HIV positive (exactly how many will be
revealed in later analyses), genetic testing of the HIV revealed that in all
cases the virus came from someone other than the main partner.
Alison Rodger told the conference that if the HIV-positive partners had not
been on treatment in this group, 50-100 (median: 86) transmissions would have
been expected in the gay couples, and 15 transmissions in heterosexual couples.
transmissions is not the same as zero chance of transmission. The researchers calculated
the 95% confidence intervals for the results seen. What this means is that they
calculated the odds of zero transmissions being the ‘true’ figure and what the
maximum possible risk of transmission was, given the results seen.
established that there was a 95% chance that (in a couple whose sexual activity is average for the group studied) the greatest-possible risk of
transmission from a partner was 0.45% per year and from anal sex was 1% a year.
a press conference, PARTNER study principal investigator Dr Jens Lundgren
pointed out that this meant that there was a maximum 5% chance that over a ten-year
period, one in ten HIV-negative partners in a gay couple who had unprotected anal sex might acquire
HIV; equally, though, it was more likely that their chance of
acquiring HIV from their partner was nearer to zero, and indeed could be zero.
the group studied becomes smaller, so confidence intervals become larger and
the certainty of a result becomes more ‘fuzzy’. This means that the maximum likely chance of transmission form someone on fully suppressive HIV therapy was 2% a year for vaginal sex with ejaculation, 2.5% for receptive anal sex, and 4% for receptive anal sex with ejaculation. This latter figure implies a more than one-in-three chance of infection if sexual behaviour remains unchanged over ten years, but again this is a 'worst case' scenario and the likelihood is probably lower.
No transmissions occurred despite
quite high levels of STIs, especially in the gay couples. When the ‘Swiss
Statement’ was released in 2008, it declared that people with an undetectable
viral load did not transmit HIV, but made an exception of people with an STI: the
PARTNER study may be telling us that STIs (in either the positive or negative
partner) don’t increase the likelihood of HIV transmission if the positive
partner is on ART and undetectable (though of course they can still be transmitted
is still recruiting gay male couples and, as noted above, its full results will
not be out till 2017. Till then we need to be cautious about what it has proved,
and, as Jens Lundgren pointed out, it will probably never be possible to show
with mathematical certainty that the risk of transmission from someone on successful HIV therapy is absolutely
zero. In addition, these results exclude situations where ART failed in the HIV positive partner, though there were relatively few of these cases.