HIV tests give false negative results for up to SEVEN MONTHS

People taking a controversial preventative HIV drug could give false negative results for up to seven months, new research suggests. 

Tests are unable to pick up the virus in those taking PrEP, a US study found.   

Infected people may then have unprotected sex thinking they are HIV free, the reserchers warn.

PrEP is approved for people at a high risk of HIV infection, such as those with an affected partner.  

Critics claim it encourages sexual promiscuity, which could increase the transmission of other sexually transmitted infections (STIs).

HIV tests give false negative results for up to seven months (stock)


This drug in particular is fixed-dose combination of two anti-retroviral drugs, tenofovir and FTC, in one pill. 

They work together to interfere with an enzyme which HIV uses to infect new cells, slowing down the virus’s attack or preventing it altogether. 

The drug is designed for people that have not yet been exposed to the virus to protect themselves against it. 

Alternatively, people who have been exposed can take PEP (post-exposure prophylaxis), a month-long course of drugs started within 72 hours of exposure.

Why does PrEP make HIV tests less accurate? 

HIV infections cause people’s immune systems to make proteins, known as antibodies, that fight the virus.

These antibodies are what HIV tests detect.    

As PrEP prevents the HIV virus multiplying, it may cause antibody numbers to rise more slowly.

This could mean it takes longer for a person to produce a sufficient number of antibodies for a test to detect them. 

PrEP users are recommended to have HIV tests every three months in case they miss a dose, however, lead author Ivana Parker, from the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, suggests they get tested every four weeks.

The CDC is looking into developing more sensitive HIV tests that detect low antibody levels, the New Scientist reported.

Tests can give false negative results for up to seven months among those taking  PrEP (stock)

Tests can give false negative results for up to seven months among those taking PrEP (stock)

How the research was carried out   

The researchers analysed the blood and saliva samples of injecting drug users.

The users, from Thailand, were taking PrEP. 

Results suggest it takes seven months before HIV-related antibodies are detected in saliva tests and three months for blood tests.  

The findings were presented at an American Society for Microbiology meeting in Atlanta. 

Scientists edge closer to an HIV vaccine 

This comes after research released last April suggested scientists are edging closer to a long-term preventative HIV vaccine.

A single injection protected monkeys against a version of the virus for at least 18 weeks, suggesting the jab could offer people months of immunity, a study by Rockefeller University, New York, found. 

Developing such a vaccine is difficult due to HIV ‘hiding’ from people’s immune systems, however, including certain proteins in the injection cause immune cells to recognise parts of the ‘envelope’ that surround the virus, the research adds.

According to the researchers, their findings, published in the journal Nature Medicine, ‘lay the groundwork’ for a preventative vaccine that could be given as little as once a year. It is unclear when it may be available.