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- One of the adenoviruses used in the Sputnik V vaccine has raised red flags in HIV vaccine trials.
- In two studies, the Ad5 vector was linked to an increased risk of HIV infection in some participants.
- This has led Sahpra to exercise extreme caution in the reviewing and approval of Covid vaccines.
The South African Health Products Regulatory Authority (Sahpra) will not approve Russia's Sputnik V Covid-19 vaccine for use in South Africa until the developer can confirm that it doesn’t make people more vulnerable to HIV infection.
On Monday, Health24 reported that the regulatory body is concerned about the use of the two-dose vaccine in South Africa, the country that carries the world’s heaviest HIV burden, stating that the jab “may increase the risk of vaccinated males acquiring HIV".
Sputnik V uses a type of virus that causes common colds, known as adenovirus. The first dose uses adenovirus 26 (Ad26), and the second uses adenovirus 5 (Ad5) to carry a harmless form of SARS-CoV-2 (the virus that causes Covid-19) into a person’s cells where it triggers an immune response.
But earlier research indicated that Ad5, the carrier virus in Sputnik V's second shot, may increase the risk of HIV acquisition in men.
Step study
Using common cold viruses in vaccines has previously been tested in non-Covid vaccine studies, but this approach, using the Ad5 vector, has led to problems in the past, according to Sahpra.
An experimental HIV vaccine from Merck & Co., known as the Step trial, primarily recruited men who had sex with men in the Americas and Australia. It was designed to test the efficacy of the vaccine in people at high risk of HIV infection. It was, however, halted in 2007 due to lack of efficacy. But evidence later showed that uncircumcised men who had been naturally infected with Ad5 before receiving the vaccine became especially vulnerable to HIV infection.
“Over extended follow-up, the increased risk of HIV among vaccine recipients became statistically significant when the entire trial population was analysed,” Sahpra said in its statement.
In a letter published by The Lancet in October 2020, scientists highlighted this concern, noting that Covid shots relying on the same vector as the Merck one “could similarly increase the risk of HIV acquisition among men who receive the vaccine”. They requested that these safety concerns be thoroughly evaluated before any further development of Ad5 vaccines for Covid-19.
Phambili study
Another past study, known as the Phambili trial, used the same vaccine and recruited heterosexual men and women in South Africa. Professor Glenda Gray – president of the South African Medical Research Council (SAMRC) and co-investigator of the Johnson & Johnson (J&J) Sisonke Covid vaccine study in SA – was the protocol chair of Phambili.
Initial findings from the Phambili study didn’t indicate an enhanced HIV risk, but the risk was confirmed after extended follow up.
The conclusion of a consensus conference in 2013, sponsored by the National Institutes of Health, “warned that non-HIV vaccine trials that used similar vectors in areas of high HIV prevalence could lead to an increased risk of HIV-1 acquisition in the vaccinated population”, wrote the authors of The Lancet editorial.
How may the vector increase HIV risk?
It’s not entirely clear how Merck's Ad5 vaccine increased participants’ risk of HIV acquisition. The Lancet editorial notes a couple of possibilities, including dampening of HIV immunity and enhancing replication of the Aids virus.
Could the same thing happen with Covid vaccines?
Despite the incidence of the Ad5-vector used in the experimental HIV vaccines increasing some of the participants’ susceptibility to HIV infection, things may be different for the Covid vaccines, but this requires research.
Professor Salim Abdool Karim, epidemiologist and former co-chair of South Africa’s Covid-19 ministerial advisory committee (MAC), told Bloomberg in February that while research is needed to show that the Covid vaccines won’t have the same effect on the immune system, it wouldn’t require additional large-scale studies.
“It doesn’t have to be a clinical study,” he said. “It could be a study in animals, it could be some laboratory marker.” The manufacturers, he said, must “show us that the Ad5 used in the HIV vaccine trial and their Ad5 are behaving differently”.
Sahpra: rolling review remains open
The developer of Sputnik V, the Gamaleya Institute, has received a request from Sahpra to provide additional data demonstrating the safety of Sputnik V in populations with HIV prevalence and incidence.
“Sahpra is concerned that use of the Sputnik V vaccine in South Africa, a setting of a high HIV prevalence and incidence, may increase the risk of vaccinated males acquiring HIV,” the organisation said.
But the institute, which falls under the Russian government’s department of health, has failed to do so. However, Sahpra added that the rolling review would remain open and that the developer would still be able to submit additional safety data in support of its application.
A number of other leading Covid vaccines, including the ones developed by Janssen (J&J) and AstraZeneca-Oxford University use different adenoviruses (Ad26) as vectors.
To date, there's no evidence that the Ad26 vector increases the risks of an HIV infection.
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