Vaccine can prevent a substantial number of cases of clinical malaria, especially in areas of high transmission rates
The first malaria vaccine candidate (RTS,S/AS01) to reach phase three clinical testing is partially effective against clinical disease in young African children up to four years after vaccination, according to data published in medical journal, The Lancet.
The results suggest that the vaccine could prevent a substantial number of cases of clinical malaria, especially in areas with high transmission rates.
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 the groups.
However, protection against the disease was prolonged by a booster dose, increasing the average number of cases prevented in both children as well as young infants.
Brian Greenwood, corresponding author and professor of clinical tropical medicine at the London School of Hygiene & Tropical Medicine, said, “Despite the falling efficacy over time, there is still a clear benefit from RTS,S/AS01. An average 1,363 cases of clinical malaria were prevented over four years of follow-up for every 1,000 children vaccinated and 1,774 cases in those who also received a booster shot. Over three years of follow-up, an average 558 cases were averted for every 1,000 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,” he added.
About the vaccine
The RTS,S/AS01 vaccine was developed for use in sub-Saharan Africa where malaria still kills around 1,300 children every day. There is currently no licensed vaccine anywhere in the world against malaria.
The phase three randomised trial enrolled 15,459 young infants (aged 6 to 12 weeks at first vaccination) and children (5 to 17 months at first vaccination) from 11 places across seven sub-Saharan African countries (Burkina Faso, Gabon, Ghana, Kenya, Malawi, Mozambique and United Republic of Tanzania) with varying levels of malarial transmission.
In 2014, the initial phase three results at 18 months showed vaccine efficacy of about 46 per cent against clinical malaria in children and around 27 per cent among young infants.
Vaccine efficacy is the reduction in the incidence of a disease (the number of new cases that occur in a population in a given period) among trial participants who receive the vaccine compared to the incidence among participants who do not receive the vaccine.
Vaccine efficacy in children
As part of the study, members of RTS,S Clinical Trials Partnership followed up the infants and children for a further period of 20 to 30 months, respectively, and assessed the impact of a fourth booster dose.
In children who received three doses of RTS,S/AS01 plus a booster dose, the number of clinical episodes of malaria at four years was reduced by just over a third (36 per cent). This is a drop in efficacy from the 50 per cent protection against malaria witnessed in the first year.
What is important is that without a booster dose, significant efficacy against severe malaria was not shown in this age group. However, in children who were given a booster dose, the overall protective efficacy against severe malaria was 32 per cent and 35 per cent against malaria-associated hospitalisations.
Vaccine efficacy in infants
In infants, who received three doses of RTS,S/AS01 plus a booster dose, the vaccine reduced the risk of clinical episodes of malaria by 26 per cent over three years of follow-up. There was no significant protection against severe disease in infants.
According to Greenwood, “The European Medicines Agency (EMA) will assess the quality, safety, and efficacy of the vaccine based on these final data. If the EMA gives a favourable opinion, WHO could recommend the use of RTS,S/AS01 as early as October this year. If licensed, RTS,S/AS01 would be the first licensed human vaccine against a parasitic disease.”
Read more about the malaria vaccine here.
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