Tag Archives: Sex

An Argument with Michael Marmot

About two decades ago I went head-to-head in an argument with the great Michael Marmot at the Medical Research Council. The topic of conversation was information that should be routinely collected in randomised trials. Marmot was arguing that social class and economic information should be collected. He made a valid point that these things are correlated with outcomes. I pointed out that although they may be correlated with outcomes, they were not necessarily correlated with treatment effects. Then came Marmot’s killer argument. Marmot asked whether I thought that sex and ethnic group should be collected. When I admitted that they should be, he rounded on me, saying that this proves his point. We met only recently and he remembered the argument and stood by his point. However, it turns out that it is not really important to collect information on the sex after all. Wallach and colleagues, writing in the BMJ,[1] cite evidence from meta-analyses of RCTs to show that sex makes no difference to treatment effects when averaged across all studies. So there we have it, a parsimonious data set is optimal for trial purposes, since it increases the likelihood of collecting essential information to measure the parameter of interest.

— Richard Lilford, CLAHRC WM Director


  1. Wallach JD, Sullivan PG, Trepanowski JF, Steyerberg EW, Ioannidis JPA. Sex based subgroup differences in randomized controlled trials: empirical evidence from Cochrane meta-analyses. BMJ. 2016; 355: i5826.



Is it Safe to Have Condomless Sex with an HIV-infected Person who is on ART?

Previous studies have suggested that the answer to the above question is ‘yes’.[1] However, the main source of this reassuring information comes from the control group of an RCT of early treatment of HIV with ART (Anti-Retroviral Therapy).[2] The control group is atypical in many respects, but particularly in that they were advised to use condoms, and the trial included primarily heterosexual couples and so results could not be extrapolated to MSM (Men who have Sex with Men).

A recent report in JAMA followed up 584 heterosexual couples and 340 MSM couples for a median of two years, where one partner in the couple was HIV positive and on ART.[3] A total of 40,000 condomless sex acts were reported – only one heterosexual and ten MSM converted. But whence the HIV! All viruses were serotyped and in no case was the new infection acquired from the partner. It seems that condomless sex with a responsible partner is pretty safe. However, the CLAHRC WM Director, mindful of his duty of care, still counsels caution. First, as he is always saying, science can’t prove a null; an even larger study may have found some cases. Second, all the infected patients had been taking ART for over six months at entry, and it is known that infectivity declines with time, even after achieving viral suppression in blood. Third, this cohort was constituted of people who had already been having condomless sex for some time and it therefore would tend to exclude those who were more prone to transmit or become infected.

— Richard Lilford, CLAHRC WM Director


  1. Daar ES, Corado K. Condomless Sex With Virologically Suppressed HIV-Infected Individuals. How Safe Is It? JAMA. 2016; 316(2): 149-51.
  2. Cohen MS, Chen YQ, McCauley M, et al. Prevention of HIV-1 Infection with Early Antiretroviral Therapy. N Engl J Med. 2011; 365(6): 493-505.
  3. Rodger AJ, Cambiano V, Bruun T, et al. Sexual activity without condoms and risk of HIV transmission in serodifferent couples when the HIV-positive partner is using suppressive antiretroviral therapy. JAMA. 2016; 316(2): 171-81.