A 25 percent efficacy for an HIV investigational vaccine was uninspiring forcing it to be stopped but provided a silver lining that will facilitate a better HIV vaccine, an HIV prevention researcher said last Thursday.
Imbokodo Zimbabwe clinical trials principal investigator Dr Portia Hunidzarira told a Humanitarain Information Facilitation Centre (HIFC) organised media science cafe that the 25 percent was below a mathematical modelling simulation where researchers had started at a first low case scenario of 30 percent, a second moderate case scenario of 50 percent and a third high case scenario of 70 percent.
“A modelling exercise that was done so that you could appreciate efficacies. Maybe something that would have a public health impact. When doing mathematical modelling exercises. We just try to give different scenarios whereby we are looking at what would happen if this would happen, or this would happen or this would happen. The y axis shows number of infections in the millions over time and the x axis shows over time between 2000 and 2030 ie 2005, 2010, 2015, 2020, 2025 and 2030,” she said. “So first scenario, if we were to do nothing with no HIV vaccine and we are just doing what we are doing now which is risk reduction, condoms, PrEP, abstinence if its there, that’s what we are doing, we expect over time, HIV infections would go down, but there is time when there is no change. Like things would just plateau, there will be no further decrease in the number of HIV infections in the present time or status quo. If say we were to introduce an HIV vaccine into the population. Say we have a vaccine with 30 percent efficacy and we vaccinate 20 percent of the population, already we can see there is an impact on HIV infections. We can see hey are going down and we actually prevent 6 million new infections over time. ”
Dr Hunidzarira said at a modest 50percent efficacy despite vaccine hesitancy, if 30 percent of the population were vaccinated, 17 million new infections would be averted.
“Then imagine we have a vaccine that is 70 percent efficacious. That’s our sweet spot. It’s very good. People don’t even want.Its ok. We cover 40 percent of the population, but look at what we can do. 28 million new infections averted,” she said.
Despite a dispiriting 25 percent efficacy and 95 percent confidence interval, Imbokodo researchers have taken the ‘if at first you dont succeed try again’ approach.
“So that is why we are so motivated to still look for an HIV vaccine. Because if we do nothing, things are just going to eventually plateau and there will be stagnancy. We still will be having these high infections but no significant drop in the number of infections. But we really would not be satisfied with the 25 percent efficacy vaccine because 30 percent does a bit,” Dr Hunidzarira said.
Dr Hunidzarira said they hoped for a confidence interval that is not in the negative as the -10,5.
“So -10.5 means we are below zero. So once the confidence interval is below zero it means in the range is a zero. So what zero means in statistics is when we have a zero in confidence interval, there is a chance that the results we get show no difference between the groups. Zero means there is nothing different. It is just the same. So you never want a confidence interval which includes a zero. That then means the 25 percent is a chance. So for us to go to stage 2 we would have been happy if our confidence interval didnt include a zero, anything above zero and whatever positive number. Then we would have gone to stage two,” she said.
The Study enrolled over 2600 female participants aged 18 to 35 across sub-Saharan countries namely Malawi, Mozambique , South Africa, Zambia and Malawi. Zimbabwe had 331 participants.
There was a vaccine arm and a placebo arm which were in a double blinded manner where the participants and investigators didn’t know who got what save for the pharmacist who prepared them.
According to the Joint United Nations Programme on HIV/AIDS (UNAIDS), women and girls accounted for 63% of all new HIV infections in this region in 2020.
“These women were determined to be at high risk of acquiring HIV infection. In Zimbabwe we enrolled about 331 women. These were enrolled at Seke South and St Mary’s Clinical Research Sites under the University of Zimbabwe Clinical Research Centre. The study vaccine schedule consisted of an injection of the AD26 which was given at baseline or the beginning of enrollment, at month 3, month 6 and month 12. Then additionally at month 6 and month 12, they got what we call a booster injection which is what we call a protein vaccine which is a Clade C gp140. It was then given at month 6 and month 12.
“So on the first visit which was at enrolment, the participant was given the injection on the left shoulder, the AD26 or placebo. But the participant didn’t know. So you would get an injection at enrollment and at month three you would get an injection . Then at month 6, you now get an injection on the left side and on the right site. Then at month 12 you get an injection on the left and right side,” said DrrHnuidzarira.