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  • HIV pre-exposure prophylaxis (PrEP) users can get other sexually transmitted infections (STIs)
  • An Ontario study found that a sizeable proportion of people were not immunized against STIs
  • Researchers encourage clinicians to use PrEP care as an opportunity to offer vaccines for STIs

PrEP

When used as directed, HIV pre-exposure prophylaxis (PrEP) is highly effective at reducing the risk of HIV infection. The most commonly used formulation of PrEP is a pill taken orally that contains two medicines—tenofovir DF and FTC. In addition to having anti-HIV activity, these drugs also work against hepatitis B virus (HBV). The combination of tenofovir DF + FTC is sold as Truvada and is also available in generic formulations.

Two hepatitis-causing viruses

PrEP guidelines recommend that clinicians screen patients prior to initiating PrEP and at regular intervals (usually every three months) for common sexually transmitted and blood-borne infections (STBBIs). The guidelines also encourage clinicians to vaccinate non-immune patients against hepatitis A virus (HAV) and hepatitis B virus (HBV). These two viruses can infect the liver, causing injury and severe illness. HBV can also cause liver cancer. Both viruses can be sexually transmitted. Vaccines against HAV and HBV are highly effective and are recommended by PrEP guidelines.

Human papillomavirus

Another common STI is human papillomavirus (HPV). Some strains of HPV can cause warts in the anus and genitals. Other strains can cause cancer in different parts of the body, such as the anus, cervix, penis and vulva. HPV can also cause tumours that can develop at the back of the tongue and in the throat. HPV vaccination is highly effective at preventing HPV-related cancer. However, PrEP guidelines generally do not recommend HPV vaccination.

An Ontario study

Researchers in Ontario have been analyzing health-related information from an ongoing study called the Ontario PrEP Cohort study. Participants, who are HIV negative, undergo regular surveys. Medical data is collected from the clinics through which participants are connected. Participants have been recruited from the following cities:

  • Guelph
  • Hamilton
  • London
  • Ottawa
  • Toronto
  • Sudbury

Researchers aim to ultimately enroll 800 people. So far, they have analyzed data from 633 participants.

A brief profile of these 633 people upon study entry was as follows:

  • age distribution: 26 years or younger – 12%; 27 to 49 years – 63%; 50 years and older – 15%
  • major ethno-racial groups: White – 60%; racialized people – 31%
  • major sexual orientations: gay – 80%; bisexual – 8%
  • having casual sex partners – 79%
  • already taking PrEP – 70%

Note that percentages do not total 100%, as some data were missing.

Results – Immunity against HAV and HBV

Among people who were using PrEP when they entered the study, immunity status to HAV and HBV were as follows:

  • HAV immune – 69%
  • not HAV immune – 17%
  • unknown status – 14%
  • HBV immune – 81%
  • not HBV immune – 15%
  • unknown status – 4%

Among people who had not initiated PrEP, figures were as follows:

  • HAV immune – 59%
  • not HAV immune – 33%
  • unknown status – 8%
  • HBV immune – 70%
  • not HBV immune – 25%
  • unknown status – 4%

Note that percentages do not total 100% due to rounding.

In general, the researchers found that people who lived in large cities, such as Ottawa and Toronto, were more likely to have been vaccinated against HBV. 

Focus on HPV

For people who get the HPV vaccine, three doses are recommended. 

Among people who were using PrEP when they entered the study, the distribution of HPV vaccination was as follows:

  • all three doses of the HPV vaccine – 17%
  • two or fewer doses (this includes people who received no dose) – 18%
  • unknown vaccination – 66%

Among people who had not initiated PrEP, the distribution of HPV vaccination was as follows:

  • all three doses of the HPV vaccine – 10%
  • two or fewer doses (this includes people who received no dose) – 17%
  • unknown vaccination – 72%

Note that percentages do not total 100 due to rounding.

Bear in mind

According to the researchers, although many participants had immunity to HAV and HBV, “a sizeable proportion was non-immune.” Furthermore, the researchers found rates of HPV vaccination “particularly low.”

The researchers encouraged clinics to promote vaccination of HAV, HBV and HPV. They noted that both HAV and HBV can cause injury to the liver. What’s more, HBV can cause liver cancer. Currently there is no treatment for HAV, and HBV can be kept under control with antiviral drugs but is not readily curable. 

In Canada, gay, bisexual and other men who have sex with men (gbMSM) are disproportionally affected by outbreaks of HAV. The researchers reported a similar trend in this population for HBV. They stated that “PrEP care represents a valuable opportunity for vaccination against [all three viruses—HAV, HBV and HPV].”

The growing importance of vaccination against HAV and HBV

As mentioned earlier, the current mainstay of PrEP—tenofovir DF + FTC (sold under the brand name Truvada and available in generic formulations)—is highly effective at providing protection from HIV and also has activity against HBV. A similar effect is found with another pill containing a different formulation of tenofovir also used for PrEP—TAF (tenofovir alafenamide) + FTC, sold as Descovy. 

In Canada and other high-income countries, a long-lasting injectable formulation of PrEP called Apretude (cabotegravir) has been approved. This drug is highly effective at preventing HIV. However, it has no activity against HBV. 

Another drug called lenacapavir, also available in a long-acting injectable formulation, is undergoing clinical trials in different populations for its ability to prevent HIV infection. However, it too does not have activity against HBV. In clinical trials, lenacapavir appears very promising as PrEP and will hopefully be approved for this use in several years.

In an era when cabotegravir, lenacapavir and other drugs will increasingly be used as PrEP, immunization against HBV will become even more important.

More on HPV

The researchers noticed a trend whereby people with higher annual incomes were more likely to have been vaccinated against HPV. This is because the vaccine is expensive and is not subsidized for people over the age of 26. 

To increase rates of HPV vaccination in Ontario, the researchers recommended that this province adopt policies used in other provinces. For instance, the researchers noted that in Nova Scotia, gbMSM who are 45 years or younger can receive subsidized access to HPV vaccination. In Prince Edward Island, the vaccine is provided at no charge to gbMSM of all ages.

PrEP has been an enormous success at reducing the risk of HIV infection. Prescribing PrEP represents an opportunity to provide care about sexual health in general. Such care should include regular screening for STIs and, when needed, vaccination against HAV, HBV and HPV.

—Sean R. Hosein

Resources

HIV pre-exposure prophylaxis (PrEP) resources – CATIE

HIV post-exposure prophylaxis (PEP) resources – CATIE

Researchers encourage simultaneous testing for three viruses—HIV, hepatitis B virus (HBV) and hepatitis C virus (HCV)CATIE News

Study with young men underscores the need for long-acting forms of HIV preventionCATIE News

REFERENCE:

McGarrity MW, Lisk R, MacPherson P, et al. HIV pre-exposure prophylaxis and opportunities for vaccination against hepatitis A virus, hepatitis B virus and human papillomavirus: an analysis of the Ontario PrEP cohort study. Sexually Transmitted Infections. 2024; in press