COVID vaccines were developed at lightning speed. So why don’t we have a HIV/AIDS vaccine?

A doctor holds a syringe.

More than 36 million people have died from AIDS-related illnesses since HIV first emerged more than 40 years ago – and yet, we still don’t have an effective vaccine.

You would be forgiven for thinking that developing a vaccine to protect against HIV should be a relatively simple task – after all, numerous COVID-19 vaccines came on stream less than a year after the World Health Organisation (WHO) declared a pandemic.

But HIV is a very different ball game. In the four decades that have passed since the virus was first detected, countless potential vaccines have failed at clinical trial stages.

On Wednesday (18 May), the world observes World AIDS Vaccine Day – each year, we reflect on how far we’ve come, while also recognising that there’s still a long road ahead to bring the HIV epidemic to an end.

HIV is a much trickier virus than COVID – and that makes developing vaccines difficult

Matthew Hodson is executive director of aidsmap, a charity that works to inform the public about the realities of HIV. He explains that HIV is a “tricker” virus than others, and it’s proven “particularly challenging” to find a vaccine that offers adequate protection.

“Whereas most other vaccines work by teaching part of the immune system to produce antibodies that clear an infection, antibodies are unable to clear HIV infection,” Hodson explains. “Many viruses, such as flu, produce an immune response that will clear the virus from the body without medication. HIV does not do this. Even when HIV is treated and suppressed, the virus can hide away deep in our DNA, so it rebounds if treatment is halted.”

Another complication is that HIV “evolves rapidly” within the body once a person has contracted the virus, meaning its make-up varies significantly from person to person.

“An effective vaccine would need to recognise and respond to a wide variety of different strains,” Hodson says.

That’s not to say there’s no hope for the future – there are a number of HIV vaccines still in development, including several that utilise the mRNA technology used in COVID vaccines. Hodson is tentatively excited about the potential, but he’s remaining cautious.

“I’ve been disappointed too often in the past. Some large trials which looked promising were recently halted because there was no evidence of effectiveness,” he says.

Hodson points out that those vaccines are still in the very early stages, so even if they do end up being successful, it would be years before they came on stream.

A HIV vaccine wouldn’t be a ‘simple fix’

He’s also keen to point out that a HIV vaccine wouldn’t be a “simple fix”, and that the HIV epidemic would likely still continue even if one was rolled out. There are a number of reasons for that.

“Not everyone who would benefit will take a vaccine, even if offered,” Hodson points out. “The COVID vaccine, which is safe and effective against severe illness, led to protests from people refusing to take it. With HIV, we have seen relatively low uptake of PrEP (pre-exposure prophylaxis, a drug taken daily that prevents a person from contracting HIV), even among communities highly likely to acquire HIV.”

Hodson also worries that people may be reluctant to take a vaccine if it’s not 100 per cent effective – which it likely wouldn’t be.

“That may further complicate people’s feelings around taking it,” he says.

There are also going to be other challenges down the line if an effective HIV vaccine was developed.

“Beyond any reluctance there may be to take an HIV vaccine, there would likely be challenges to ensure everyone had access to it,” Hodson says. “We’ve been able to treat HIV effectively for more than a quarter of a century but still one in four people who live with HIV globally are not on treatment. Developing a vaccine that works may only be half the battle, there also needs to be the money and the healthcare structures in place to ensure everyone can access it.”

If a vaccine ever comes on stream, it can’t just be offered to at-risk communities

Sarah Fidler is professor of HIV and communicable diseases at Imperial College London – she’s excited about the prospect of a potential HIV vaccine coming on stream in the future, but she holds similar concerns to Hodson about how the world can make sure those most vulnerable can access it.

“It would be huge [if we got a vaccine],” Fidler says. “HIV, in many parts of the world, is still a huge concern. If we could vaccinate children as they develop and become sexually active so they knew they couldn’t catch HIV, that would be extraordinary. Unfortunately HIV hasn’t gone away – a lot of people don’t really think about it, but in some communities it’s causing huge problems. Parts of sub-saharan Africa and Asia, HIV is affecting one in four or one in five people in their communities.”

It’s vital that the world continues trying to develop a vaccine for those people – but there are concerns that the stigma around HIV could deter people from getting jabbed.

“The fact that HIV still carries this terrible stigma is, I think, a failure of us who work in the field. Pretty much everyone has sex at some point in their lives – why we’ve decided to be so judgemental about it, I have no idea, but it’s pretty appalling that in 2022 living with a health condition should be so stigmatised. Clearly we need to do a much better job at removing that stigma.”

Professor Sarah Fidler.

Professor Sarah Fidler. (Provided)

One way to get around that would be to offer a vaccine to every child under the age of five. Doing so would make it a routine procedure rather than just vaccinating those considered at risk.

“In countries like the UK where the prevalence of HIV is much lower and it is affecting some core groups, my concern would be that, cost effectiveness wise, you could argue that we don’t need to vaccinate every single child, but I would say, take away anything to do with sexuality and just offer it to everybody. That would clearly remove any stigma because it’s not about your behaviour or your personality, we’re just protecting you and keeping you healthy.”

Effective treatment and PrEP have changed the game for HIV

It’s also worth noting that much has changed in the fight against HIV since the early days of the epidemic. Today, we have effective treatment, which means people with HIV can live long, healthy lives – so long as they can actually access the right medication. We also have PrEP – when taken daily, it prevents a person from contracting HIV even if they’re exposed to it through sex. A vaccine would help enormously in the fight to end the HIV epidemic, but it’s also important to remember that we already have vital tools at our disposal, Hodson says.

“We have to recognise that what it means to live with HIV has changed enormously in the year of effective treatment. Someone diagnosed with HIV now who has access to treatment should have the same life expectancy of someone who does not have the virus. The knowledge that we can’t pass the virus on to our sexual partners when we are on treatment is liberating. It has the power to challenge much of the stigma we face, however that fear and ignorance persists. We see it on Grindr, we encounter it in our daily lives.”

He continues: “It’s all too easy to put all of our hopes into the idea that an effective vaccine will end not only the epidemic, but the stigma that people face. This is by no means certain. A vaccine is not a cure, a vaccine will not change the HIV status of people who live with the virus. PrEP already demonstrates that some of the fear of people living with the virus is not just based on fear of infection.”

That’s echoed by Professor Fidler. She points out that those on effective treatment have an undetectable viral load – they can’t pass HIV on through sex, childbirth, blood transfusion, or any other method.

“That’s really important – all people living with HIV on medication can’t pass it on. That has really transformed people’s lifestyles, people’s experiences. You can enter into a new relationship and as long as you know your viral load is undetectable, you choose when you disclose your status – you don’t have to share your status with everybody you choose to have sex with because you know you’re safe. That’s really, really important.”

While we’re waiting on a vaccine, Fidler is hoping that we can ramp up testing – that means more and more people will be on effective treatment, which will result in fewer people passing it on.

“There’s no judgement, but if you’ve had sex and not used condoms, we recommend that people get tested for HIV. It’s very easy to do that now – you can do it in the post, you can do it from your own home. Making things easy for people is key.”