While there are many wonderful successes with vaccine trials, it must also be noted that there are a fair share of trials where the results have been disappointing. It's lovely to enjoy the successes of trials, but it's equally important to acknowledge where trials have gone wrong so that we can avoid more costly trials in the future. I'm going to have a look at three recent cases where trial results seemed to fall dramatically short of what was hoped:
- Dengue fever
Results reported in the Lancet in September 2012 showed mixed results following the first large-scale trial of the vaccine carried out by Sanofi. While the vaccine was effective in defending against 3 out of 4 of the viral subtypes, scientists were left scratching their heads over the failure to defend against an aggressive 4th subtype known as â€˜dengue serotype 2'. Researchers had hoped the vaccine would confer at least a 70% reduced risk of getting dengue, but the trial in Thailand – where dengue serotype 2 is prevalent – showed a disappointing 30.2% reduced risk. The results shouldn't be too disheartening, however, as it should be remembered that the trial did show good efficacy against the other three strains.
The Bill & Melinda Gates Foundation's aim to develop a vaccine against malaria was delivered a heavy blow in November 2012, when a large phase III clinical trial of the RTS,S/AS01 vaccine candidate showed disappointing results. The key target age group in the trial was babies aged 6-12 weeks, and follow-up after 12 months showed that the number of episodes of malaria was reduced by only one-third compared to the control group. This figure of one-third is considered to be too low for the vaccine to be useful clinically, with a WHO-led consortium stating that this figure should be above 50%. Again, however, positive aspects can be drawn from the trial, with many scientists lauding the infrastructure of a trial that is inherently difficult to conduct.
The first major vaccine trial against TB in infants since 1921, when the Bacillus Calmette-Guerin (BCG) vaccine was introduced, yielded disappointing results in February 2013. The latest and most advanced vaccine MVA85A failed to give the babies the required protection against TB. MVA85A was designed to boost the effect of the BCG vaccine, but the efficacy it added was statistically insignificant. This is the first vaccine in a series to be tested, however, so this is by no means the end for TB vaccine development.
Is there a way we can avoid costly trials that give disappointing results in the future?
What positives can be drawn from a trial with disappointing results?
You can join our discussion on LinkedIn or leave a comment below, I'd love to hear what you think.
If you'd like to know more about research and development in vaccines, including vaccines against dengue fever, malaria and TB, you might like to consider attending the World Vaccine Congress and Expo 2013 on the 16-18 April 2013, Gaylord National Hotel and Convention Center, Washington DC.