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Not everyone is on board with the idea that public health institutions should be celebrating sex, much less recreational sex, or that PrEP should be elevated to a status traditionally reserved for condoms.

The Los Angeles-based AIDS Healthcare Foundation, billed as the largest in the world, has promoted the “same clear message” for nearly 25 years: “If you’re having sex, you need to use a condom, consistently – every time.” The charity has unapologetically promoted stark ads like a recent “Syphilis is Serious” campaign that depicts syphilis sores and a “Drug-Resistant Gonorrhea Alert!” counterpart in which the conjoined bacteria resemble underwater mines.

Few PrEP critics have been more outspoken than Michael Weinstein, the foundation’s president. In 2014, the foundation released a blistering “What if you’re wrong?” takedown of the CDC’s decision to back PrEP as an additional HIV prevention tactic.

Amid growing evidence of good adherence and successful prevention, the foundation softened its stance in 2015 to seek “common ground” on PrEP. In a 2017 op-ed, though, Weinstein and two foundation scientists remained deeply sceptical. In the journal AIDS, they wrote that although the pill is highly effective when taken correctly, the data on uptake, adherence and risky behaviour suggested that it had not achieved “the positive impact anticipated by the CDC”.

Foundation spokesman Ged Kenslea emphasises that although the charity isn’t questioning PrEP’s clinical effectiveness, “there is concern about deploying it as a community-wide public health intervention”.

In particular, the foundation believes decreased condom use by men on PrEP is “a contributing factor to the explosion of STDs”. The organisation remains concerned about adherence as well, though Kenslea is optimistic that the ongoing development of a long-acting implant, akin to a contraceptive implant, could make PrEP’s effectiveness far less dependent on daily compliance.

Even so, he questions whether the pill in its present form deserves credit for helping to dramatically reduce San Francisco’s HIV transmission rate. “It could be that people who are at higher risk for HIV acquisition have been priced out of that city,” Kenslea says.

That view isn’t widely shared, though epidemiologists agree that the HIV/AIDS crisis is far from over. In a 2016 analysis, the CDC warned that if the rate of new HIV diagnoses remained constant, half of all gay and bisexual black men and a quarter of their Latino counterparts in the US would become HIV positive within their lifetimes.

Even in wealthy countries, public health agencies are still struggling to get anti-HIV drugs – whether as treatment or prevention – to those who need them most. In the US alone, the CDC estimates that 1.1 million people could benefit from taking PrEP; as of mid-August 2018, higher estimates suggested that only 220,000–225,000 were on it. Surging bacterial STI rates have compounded health concerns, especially since they can heighten the risk of HIV.

The soaring cost of the medicine is no small barrier, with discounted prices at local US pharmacies now averaging more than $1,700 for 30 tablets. Most of the country’s insurers negotiate lower costs and pick up much of the tab, but out-of-pocket deductibles can still run into the thousands every year. Gilead offers a co-pay assistance programme to cover those costs as well, but uninsured patients who aren’t eligible for financial assistance and who cannot access city- or state-sponsored aid are often out of luck.

Activist groups like PrEP4All are pushing for lower costs and wider availability of generic alternatives to get more at-risk people on the pill, reflecting growing concern over the sustainability of PrEP programmes given the limited budgets of many public health agencies.

If the thorny questions of access and cost can be resolved, multiple researchers and health officials say PrEP could be a tipping point in the fight against HIV.

That effort has received a crucial boost from a new draft statement by the US Preventive Services Task Force, in which the independent panel recommends that primary care doctors offer PrEP to everyone at high risk of acquiring HIV. The recommendation carries an “A” grade, denoting high certainty of a “substantial” net benefit. If the task force finalises its recommendation, federal law would mandate that insurers cover it without requiring a copayment.

According to the CDC, taking the pill consistently and as indicated reduces the risk of acquiring HIV by 92 per cent among gay and bisexual men, though a 2014 study suggested that “optimal” use of the pill – verified by the drug’s presence in blood samples – may reduce the risk by nearly 100 per cent.

Documented failures of PrEP in preventing HIV have been exceedingly rare: to date, researchers have reported only a handful of cases in people who took the pill consistently.

For commercially available condoms, the story is different. In a 2015 analysis of two studies of gay men who reported that their HIV-positive partners “always” used condoms for insertive anal sex with them, the effective prevention rate was estimated at only 72 per cent. According to the CDC’s HIV Risk Reduction Tool, in fact, having anal sex with an HIV-positive partner who is using a condom is three to four times as risky as using PrEP for protection instead.

And if an HIV-positive individual’s viral load has been reduced to undetectable levels by antiretroviral therapy for at least six months, the CDC and other agencies agree that there’s effectively no risk of transmitting the virus to any sexual partners (a concept known as “Undetectable = Untransmittable”).

Demetre Daskalakis, deputy commissioner at the New York City Department of Health and Mental Hygiene, says that although (cheap and readily available) condoms are the right prevention option for many, hectoring the public to use them has lost its effectiveness.

For years, health officials told people they would die without using condoms; ads featured the Grim Reaper, a giant scorpion, skeletons having sex and other overt references to death.

The addition of PrEP and treatment as prevention to public health toolkits means that many people are no longer “scared for their lives” when they have sex, Daskalakis says. “I think human nature would say that they use condoms less frequently, and so that’s what we’re given,” he says. “We need to evolve how we strategise STI prevention.”

He credits the “explosive jump” in PrEP and the city’s embrace of sex-positive messaging as major contributors to the nearly 15 per cent drop in new HIV diagnoses among gay and bisexual men from 2015 to 2016. “If you acknowledge that some of people’s sex lives is for pleasure, if you acknowledge that and say, ‘Embrace the pleasure in your sex life, but make a plan to keep yourself healthy,’ all of a sudden, this all flows better versus, like, ‘Don’t have sex or you’re going to die,’” he says.

And for STIs other than HIV? “PrEP will not – at least the drug – prevent STIs,” he says. “Although boy will it if you’re doing the testing right and the treatment right.”