Final trial data, published in the Lancet has disclosed that the first malaria vaccine candidate (RTS, S/ASO1) to reach phase 3 clinical testing is partially effective against clinical disease in young African children up to four years after vaccination.
The results suggest that the vaccine could prevent a substantial number of cases of clinical malaria, especially in areas of high transmission.
According to sciencedaily.com, the findings reveal that vaccine efficacy against clinical and severe malaria was better in children than in young infants, but waned over time in both groups. However, protection was prolonged by a booster dose, increasing the average number of cases prevented in both children and young infants.
The corresponding author and Professor of Clinical Tropical Medicine at London School of Hygiene & Tropical Medicine in the UK, Brian Greenwood, explained that, “Despite the falling efficacy over time, there is still a clear benefit from RTS, S/AS01.
According to Greenwood, an average 1363 cases of clinical malaria were prevented over 4 years of follow-up for every 1000 children vaccinated, and 1774 cases in those who also received a booster shot. Over three years of follow-up, an average 558 cases were averted for every 1000 infants vaccinated and 983 cases in those also given a booster dose.
“Given that there were an estimated 198 million malaria cases in 2013, this level of efficacy potentially translates into millions of cases of malaria in children being prevented.
“The RTS, S/AS01 vaccine was developed for use in sub-Saharan Africa where malaria still kills around 1300 children every day. There is currently no licensed vaccine against malaria anywhere in the world.
“The phase 3 randomised trial enrolled 15459 young infants (aged 6 to 12 weeks at first vaccination) and children (5 to 17 months at first vaccination) from 11 sites across seven sub-Saharan African countries (Burkina Faso, Gabon, Ghana, Kenya, Malawi, Mozambique and United Republic of Tanzania) with varying levels of malaria transmission. In 2014, initial phase 3 results at 18 months showed vaccine efficacy of about 46 per centagainst clinical malaria in children and around 27 per cent among young infants.”
Speaking on the children who received 3 doses of RTS,S/AS01 plus a booster, Greenwood said the number of clinical episodes of malaria at 4 years was reduced by just over a third (36 per cent), adding that this was a drop in efficacy from the 50 per cent protection against malaria seen in the first year.
He added that without a booster dose, significant efficacy against severe malaria was not shown in this age group. However, in children given a booster dose, overall protective efficacy against severe malaria was 32per cent, and 35 per cent against malaria-associated hospitalisations.
Greenwood also explained that in infants who received 3 doses of RTS,S/AS01 plus a booster, the vaccine reduced the risk of clinical episodes of malaria by 26per cent over three years follow-up. There was no significant protection against severe disease in infants.


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