Research sheds light on changes in PrEP use over time in San Francisco and Australia

Image: Africa Studio/

More than half of people who started HIV pre-exposure prophylaxis (PrEP) in a large health maintenance organisation in San Francisco were still using it five years later, but gaps in the PrEP care continuum raised the risk of HIV acquisition, researchers reported last week at the 23rd International AIDS Conference (AIDS 2020: Virtual).

Another study of PrEP scale-up in Australia found that use increased over time, shifting toward younger people and those living outside of inner cities. Many people stopped taking PrEP or did so inconsistently, but the researchers stressed that this may reflect appropriate modification of PrEP use as an individual's HIV risk changed.

Long-term PrEP use in San Francisco

Dr Jonathan Volk of Kaiser Permanente San Francisco and colleagues looked at long-term PrEP outcomes in this large clinical practice, which combines care provision and health insurance.


person years

In a study “100 person years of follow-up” could mean that information was collected on 100 people for one year, or on 50 people for two years each, or on ten people over ten years. In practice, each person’s duration of follow-up is likely to be different.


The transition period from infection with HIV to the detectable presence of HIV antibodies in the blood. When seroconversion occurs (usually within a few weeks of infection), the result of an HIV antibody test changes from HIV negative to HIV positive. Seroconversion may be accompanied with flu-like symptoms.


continuum of care

A model that outlines the steps of medical care that people living with HIV go through from initial diagnosis to achieving viral suppression, and shows the proportion of individuals living with HIV who are engaged at each stage. 

on demand

In relation to pre-exposure prophylaxis (PrEP), on-demand dosing is an alternative term for event-based dosing. See ‘event based’.


An umbrella term for people whose gender identity and/or gender expression differs from the sex they were assigned at birth.

The researchers used electronic health records to identify Kaiser Permanente Northern California members who were linked to PrEP care between July 2012 – the month daily Truvada (tenofovir disoproxil fumarate/emtricitabine) was approved for HIV prevention in the US – and March 2019.

Most (95%) of the 12,963 members linked to PrEP care were men. Half were white, 21% were Latino, 15% were Asian and 7% were African American. The proportions of white and black people who started PrEP reflect their share of the city's population, but Latinos were slightly overrepresented (15% of the population) while Asians were substantially underrepresented (35% of the population).

Of those linked to PrEP care, 10,310 members (80%) received a prescription and 8571 (66%) filled it within six months. Black Kaiser members were less likely to receive a PrEP prescription, less likely to fill it and more likely to discontinue PrEP, Volk reported.

Over five years of follow-up, the average duration of PrEP use was 1.9 years. One year after initiation, nearly three-quarters remained on PrEP. This fell to 64% at two years, but thereafter declined more slowly, to 60% at three years, 57% at four years and 56% at five years. Among those who discontinued PrEP at any point, 37% restarted it.

"Among those who discontinued PrEP at any point, 37% restarted it."

A total of 136 new HIV infections were observed during the study, including 42 in people who were diagnosed when they were first linked to care. Only six people who remained on PrEP acquired HIV, all of whom reported less than optimal adherence.

Most new infections occurred among people who were linked to PrEP care but never received a prescription (37 cases, or 1.4%), those who received a prescription but never filled it (13 cases, or 0.8%) and those who started PrEP but later discontinued it (38 cases, or 1.5%).

"We observed high levels of PrEP uptake and persistence over five years and no new HIV infections with consistent use," the researchers concluded. "Efforts are needed to reduce racial inequities and support persistence during periods of HIV risk."

PrEP scale-up in Australia

Dr Nicholas Medland of the Kirby Institute at the University of New South Wales in Sydney described outcomes including uptake, adherence and HIV seroconversion as Australia scaled up its national PrEP programme. PrEP has been subsidised by the Australian government since April 2018, and it has been actively promoted, especially for gay and bisexual men.

The researchers analysed 35,909 patients prescribed PrEP between April 2018 and March 2020. Almost all recipients were men, with just 1.5% of prescriptions written for women. The researchers noted that the available data do not allow them to separate out cisgender and transgender men and women. The average age of PrEP recipients was 35 years.

In September 2019, 52% of PrEP recipients lived in inner urban areas, falling to 49% in March 2020. PrEP use was highest in New South Wales, at 39%, followed by Victoria and Queensland, at 30% and 16%, respectively.

By March 2020, a total of 9548 people had discontinued PrEP for more than four months. Of these, 3549 (14%) restarted PrEP after the gap.

The researchers estimated that the median level of PrEP coverage – that is, the proportion of days covered by PrEP during the past three months assuming daily use – was 91%. Nearly two-thirds of recipients (62%) were categorised as having high PrEP use (more than 80% of days covered) while 24% had reduced coverage (less than 60% of days covered).

"The successful scale-up of PrEP was a 'source of great pride'."

Women were significantly more likely than men to have reduced PrEP coverage (39% vs 21%) and much more likely to discontinue PrEP for more than three months (69% vs 26%). Younger people (age 18 to 29 years) and those whose doctors were located outside inner urban areas and had a smaller PrEP caseload were also more likely to have reduced coverage or long gaps in PrEP use. Being a recipient of government benefits was also a predictor of discontinuation.

Overall, 24 new HIV infections were observed among people who had been on PrEP for more than 60 days, for an incidence rate of 0.95 per 1000 person-years. Fourteen such cases were among people who had discontinued PrEP, for a rate of 2.78 per 1000 person-years.

In summary, PrEP uptake in Australia has been "rapid and sustained", resulting in successful scale-up in the target population, which Medland said was a "source of great pride."

The researchers noted that high rates of reduced PrEP consumption and discontinuation may reflect national guidelines that recommend on-demand (before and after sex) PrEP and periodic usage depending on current risk, but they acknowledged that the findings suggest social determinants of health also play a role.

With regard to women, Medland suggested that the low PrEP uptake and high rate of discontinuation may reflect appropriate use according to guidelines (for example, changes in PrEP use related to pregnancy or using PrEP temporarily when a partner is starting antiretroviral therapy), but they may also indicate a failure to identify the role of PrEP use among women.


Volk J et al. PrEP continuum of care and new HIV infections: Long-term follow-up in a large clinical cohort. 23rd International AIDS Conference, abstract OAC0807, 2020.

Medland N et al. Successful national PrEP scale-up in Australia: Evaluation of uptake, adherence, discontinuation and HIV seroconversion from April 2018 to September 2019 using national dispensing data. 23rd International AIDS Conference, abstract OAC0802, 2020.