The Ins and Outs of HIV Transmission and Prevention

April 28, 2022

HIV prevention is an important pillar of public health. With STI rates climbing in many countries, it is important that there is a renewed focus on STI and HIV education. Helping to create awareness of HIV transmission, treatment, and risks will reduce stigma and misinformation. Addressing concerns such as whether there are risks with blood transfusions and donations, what prevention methods are available such as pre-exposure and post-exposure prophylaxis, the cost of PrEP and PEP, how to get access it, and the PrEP and PEP side effects will help increase awareness and help reduce HIV transmission.

For over forty years, HIV has continued to impact many lives. Thankfully, researchers have made advances that have led to effective treatments. These advancements have changed the management of HIV and allowed those who live with HIV to expect to live as long as their peers. Preventative treatments are taken either pre-exposure (PrEP) or post-exposure (PEP) to help stop a permanent HIV infection from taking hold in the body. And with an HIV cure and vaccine closer to reality, it provides hope that the world can beat HIV.


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What is HIV?

HIV stands for human immunodeficiency virus. It is a virus that attacks white blood cells in the immune system that helps the body fight infection, making the individual more vulnerable to other infections and diseases. These cells stay infected for the rest of their lives. HIV belongs to a group of viruses called retroviruses.

With the amazing work over the past four decades, HIV is now a manageable chronic condition. If left untreated, it can cause a weakened immune system or acquired immune deficiency syndrome (AIDS).

What is the Difference Between HIV and AIDS?

Often, the two terms are used interchangeably, leading to confusion and more misinformation about HIV.

While HIV is the virus that causes the infection, AIDS is an umbrella term for the illnesses that occur due to untreated HIV infections, where the immune system becomes severely damaged and is unable to fight infections. It is important to note that these illnesses or symptoms can vary for each individual and can include serious or critical diseases such as cancer.

One way to remember that there is a difference is that every person with AIDS lives with HIV, but not every person who lives with HIV has or will develop AIDS. With advances in treatment and care, far fewer people are developing AIDS. Often, those who develop AIDS have never been tested for HIV and treated, showcasing the importance of global equitable testing access. As treatment is highly effective, death due to AIDS can be prevented once an individual is on treatment.

How Can you Get HIV?

HIV is found in the bodily fluids of someone who is infected. This includes:

  • Semen
  • Vaginal and anal fluids
  • Blood (including through blood transfusions)
  • Breast milk

HIV can be transmitted through the exchange of body fluids from infected people through:

  • Unprotected sex
  • Sharing needles, syringes, or other injecting equipment
  • Transmission from the mother to the baby during pregnancy, birth, or breastfeeding
  • While the chance of transmission through oral sex is low, it is dependent on different factors, including whether you give or receive oral and the oral hygiene of the person giving the oral sex
  • Receiving unsafe injections, blood transfusions and tissue transplantation, and medical procedures that involved unsterile cutting or piercing
  • Accidental needlestick injuries, including among health workers

As a fragile virus, it cannot survive outside the body for long, and it cannot be transmitted through sweat, urine, or saliva. It is NOT transmitted through:

  • Kissing
  • Hugging
  • Shaking hands
  • Sharing personal objects
  • Food or water

Risk of Blood Transfusions for HIV Transmission

Blood transfusions in higher-income countries are safe and effective, and blood services work hard to minimize the risks. Blood services such as the Canadian Blood Services and the Red Cross take many actions to protect the blood supply and ensure a safe system for both donors and recipients. Donor education, risk questioning, and blood testing provide a layered approach to reducing the risk.

And while the risk is incredibly low, it can never be zero. According to the Canadian Blood Services, while every donation is quarantined and tested before it is approved for distribution to hospitals, there is still a short period when HIV cannot be detected. This is the timeframe when a donor has been recently infected, and the infection is not picked up by testing. Blood collected during this time could infect the recipient. New technology such as nucleic acid testing (NAT) that detects the virus before the body responds has significantly reduced the window period, but it has not been completely eliminated.

This is because it takes the virus time to replicate, and it is hardest to detect in the first days after infection. It is important to know that this does not mean the virus cannot be transmitted. NAT has reduced the length of time HIV can go undetected in a person infected with the virus to approximately 9 days.

So, in addition to testing, blood services also ask donor screening questions and implement strict deferral periods following travel or certain activities to help reduce the risk to transfusion recipients as much as possible.

The risk of a potentially infectious donation being collected during the window period is very low in Canada. The estimated residual risk of acquiring HIV from a blood transfusion (as of 2015) was 1 in 21.4 million donations. There are approximately 1 to 8 HIV-positive donations a year out of 1 million in Canada, but these are detected and removed from the supply. Since the implementation of blood testing in 1985, there have been no cases of transfusion-transmitted HIV in Canada.

The Canadian Blood Services collects approximately 450 mL for transfusion during the donation process. A small amount of blood is kept aside and sent to a laboratory to test for various diseases, including HIV. The NAT method is also used to test for hepatitis C (HCV) and the West Nile Virus (WNV) in the blood.

Other countries, such as the United States (where the CDC and FDA are responsible for ensuring the safe supply of blood), show similar risk levels and screening and donation processes. The American Red Cross reports that the frequency of detecting HIV-1 is about 1 in 33,000 donations screened, and HIV-2 is even rarer at 1 per 57 million donations, with a total rate of only 5% of blood donations identified as such since HIV-2 screening began in 1992. The residual risk is estimated at 1 in 1.6 million for HIV (as shown by a National Library of Medicine study using the transfusion-transmissible infections monitoring system).

However, it is important to note that some low-income countries may not be sufficiently equipped to check all blood donations, and although very rare, there have been cases of donated blood products found to contain HIV. This showcases the importance of equitable testing worldwide, both for blood donations and for individuals to know their status to help to reduce the risk of further transmission.

The FDA also reminds people that if someone has ever tested positive for HIV, they should not donate blood, even if they are on antiretroviral treatment (ART). Though there have been no reported cases of HIV transmission to transfusion recipients from blood donated in this scenario, it is still important to remain vigilant to protect from any risk of transmission.


With effective treatments for individuals living with HIV, it is now possible for those on ART to have undetectable levels of HIV. This is a phenomenal achievement and shows how far the world has come in helping not only treat HIV but help prevent further transmission.

U=U means ‘Undetectable = Untransmittable’ and is a campaign explaining how the sexual transmission of HIV can be stopped. When a person living with HIV is on effective treatment, the viral load lowers. When levels are extremely low (below 200 copies/mL of blood measured), it is considered an undetectable load, or virally suppressed. This means that HIV cannot be passed on sexually at this stage, but it is important to note this applies to sexual activity only.

This is also why it is important that if someone has ever tested positive, they do not donate blood. And while effective treatments reduce the risk of transmission through breastfeeding, it does not reduce the risk to zero, though initial studies show that the risk is very low.

HIV Prevention

Thankfully, the advances in HIV research have made prevention and treatment more effective. Different medications, sexual protection such as condoms (male and female), and accessible and accurate testing help reduce the transmission of HIV.


Testing is a vital pillar in HIV prevention – after all, the only way to know is to get tested. Forty years ago, there were no reliable tests for HIV, and when they did come on the market, they weren’t always accessible to everyone.

Thankfully, today, tests are accurate, can detect HIV earlier than past tests, and in the case of the INSTI® HIV-1/2 Antibody Self Test, offers results in just one minute! It is now easier to know your status with the ability to test at home, at mobile testing clinics, and large-scale testing events.

As symptoms can take years to develop, testing is crucial to reducing the global infection prevalence rate. In the US, nearly 40% of new HIV infections are transmitted by people who do not know they have the virus, showcasing the importance of testing to get people the treatment and care they need and help reduce unknown transmissions.


One of the advancements that have made a considerable difference in the fight against HIV is PrEP (Pre-Exposure Prophylaxis) and PEP (Post-Exposure Prophylaxis). While the two treatments are different, they are both intended to help reduce the risk of HIV transmission. PrEP is a treatment taken to help prevent HIV transmission for those who are currently negative but may be at risk, and PEP is a treatment taken after possible exposure. Prophylaxis means “treatment or actions taken to prevent a disease.”


PrEP is a prevention method used by HIV-negative individuals at high risk of being exposed to HIV through sexual contact or injection drug use. PrEP works to help keep the virus from establishing an infection when someone is exposed.


PEP is the use of antiretroviral drugs for HIV-negative individuals after a single high-risk exposure to stop HIV infection. PEP must be started as soon as possible to be effective, always within 72 hours of possible exposure, and continued for four weeks.


Check out this great video from Greater than AIDS that explains the difference between PrEP and PEP.


What Do PrEP and PEP Cost?

The cost of a test varies by where an individual lives. In places where there is publicly-funded healthcare, PrEP and PEP are often covered by healthcare. Coverage may vary by health region, such as in Canada, where the provinces administer healthcare. PrEP is available by prescription and usually requires necessary medical follow-up. It does not need to be prescribed by an HIV specialist, but not all providers are knowledgeable about PrEP, so it can be difficult to connect with a healthcare provider for PrEP and PEP. Generally, the cost in Canada is covered by most public and some private healthcare insurance plans. PrEP is available from NHS sexual health clinics in the UK free of charge.

PrEP and PEP are also available by prescription by any provider licensed to write prescriptions in the US. Many community health centers in the US offer a PrEP consultation and an HIV test (as you must be HIV negative to take PrEP or PEP). In most cases, PrEP and PEP are covered by almost all health plans under the Affordable Care Act. If there is no available coverage, resources are available to help people pay for PrEP and the necessary clinical visits and tests. Check out’s HIV Services Locator to find services near you.

How Do PrEP and PEP Work?

PrEP interferes with the pathways that HIV uses to cause a permanent infection. For HIV to cause infection, the virus needs to gain entry into the body, infect immune cells, replicate within these immune cells, and then spread through the body.

When PrEP is taken as instructed, the medicine (in this case, antiretroviral treatment/drugs) gets into the bloodstream and genital and rectal tissues to help prevent HIV from replicating within the body’s immune cells help prevent a permanent infection. Taking PrEP consistently as prescribed is vital as the levels of drugs in the body must remain high to work.

PEP also interferes with the pathways that HIV uses to cause a permanent infection but is taken after exposure. PEP also gets into the bloodstream and genital and rectal tissues and helps prevent HIV from replicating within the body’s immune system, helping prevent a permanent infection from developing. PEP must be taken as soon as possible after exposure but no more than 72 hours afterward and continue for 28 days. Like PrEP, the drug level must remain high to help prevent infection.


HIV is a serious infection, and it is important to continue using prevention methods such as safe sex, clean needle programs for those who inject drugs, regular testing, the use of PrEP to reduce the risk of HIV infection, and PEP for possible HIV exposure. With more awareness of the different tools available to people, it is possible to continue reducing the number of HIV infections and transmissions.


Aids Map:

Aids Map:

Aids Map:

Aids Map:

Aids Map:

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Canadian Blood Services:

Canadian Blood Services:



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