A malaria vaccine studied in more than 15,000 African children has been found to reduce the number of cases of disease by 27 to 46 percent.
That's only modest efficacy compared to most accepted vaccines. But this would be the first anti-malarial immunization on the market, and its developers emphasize that it still prevents a lot of cases. Its main sponsor, GlaxoSmithKline, says it's good enough to justify seeking regulatory approval in 2014.
Specifically, for every 1,000 toddlers who had the three-dose vaccination, there were 941 fewer cases of malaria over the following 18 months. Those who didn't get the vaccine had 1,800 cases per 1,000 children — a rate reflecting the fact that most of them suffer more than one case a year.
Preventing 941 cases for every 1,000 young children vaccinated "suggests that it has potential for a pretty big public health impact," says Dr. David Kaslow of the PATH Malaria Vaccine Initiative, one of the study's sponsors. "Those are some pretty big numbers of cases averted."
The new data, presented Tuesday at a malaria vaccine conference in Durban, South Africa, extends results released last November, which gave the first indication that this vaccine, called RTS,S, has limited effectiveness.
But Dr. Moncef Slaoui, chief of vaccine development at GlaxoSmithKline, says even a vaccine of modest effectiveness can have a big impact because malaria is such a monumental problem in Africa.
"Malaria in sub-Saharan Africa kills around 600,000 children every year, which is an enormous number," Slaoui tells Shots. He's been working on the RTS,S vaccine for nearly 30 years.
The African study, which involves 11 sites in seven countries, couldn't demonstrate the vaccine's impact on malaria deaths. That's because children in the study all got the very best treatment, so very few died of the disease. But those who got the vaccine were 36 percent less likely than those who didn't to get severe malaria, which often results in death for many victims.
Still, malaria specialists acknowledge that it's not going to be easy to decide how to use the RTS,S vaccine.
The new data show that 18 months after vaccination, it's 46 percent effective in preventing illness in children immunized between 5 months and 17 months of age. For infants younger than that, it was only 27 percent effective. Those efficacy rates are somewhat lower than shorter-term results presented last year, indicating that the protection falls off a bit over time.
Work is underway to see if a booster shot can strengthen that protection.
"There's no question that everybody would want a higher efficacy on this vaccine," says Dr. Johanna Daily of Albert Einstein College of Medicine. Standard vaccines against other diseases have over 80 percent, sometimes 90 percent, efficacy, she says. "But malaria has always been such a challenge. And we may not ever get those levels."
Even when people actually catch malaria — the most effective, though undesirable, form of immunization — protection against future infection is far from complete.
"It's hard to improve upon nature," Daily says. "So perhaps ... a more efficacious vaccine is unlikely, and therefore [RTS,S] would be the thing to go with."
About two dozen other malaria vaccines are in the pipeline. Some target more than one protein on the malaria parasite's surface, and some aim to protect at more than one stage in the parasite's complex life cycle. But it's going to be awhile before anyone knows if these other candidate vaccines are more effective than RTS,S.
Meanwhile, if the World Health Organization gives the green light to the Glaxo vaccine, it's going to have to compete for scarce public health funds with other malaria-prevention measures, such as insecticide-treated bed nets to keep malaria-infected mosquitoes away from sleeping children.
Figuring out the vaccine's role in malaria prevention is "going to be a very tough question," Daily says.
"Each country is going to have a pot of money and [is] going to have to decide how to spend it," she says. "Should it go to vaccine? Should it go to bed nets? Should it go to diagnosis? Should it go to community health workers? Each Minister of Health can decide if this is something they want to put their money toward."
Glaxo has pledged to keep the cost of the vaccine low — no more than the cost of production plus a 5 percent profit that the company says it will devote to developing other vaccines against neglected diseases. Slaoui says RTS,S won't be pennies per dose. Most likely, it'll be a few dollars.
RENEE MONTAGNE, HOST:
And there's new information on a vaccine against one of the world's biggest health problems, malaria. It's the only malaria vaccine in large-scale human trials. The effect of the vaccine persists for as long as a year and a half and for some young children, it cut the number of cases by half - which is progress, though most childhood vaccines provide at least 90 percent protection. Still, as NPR's Richard Knox reports, experts say they are optimistic about the results.
RICHARD KNOX, BYLINE: It's taken nearly 30 years and roughly half a billion dollars to get to this point - solid results from a study of more than 15,000 children across Africa with a vaccine called RTSS. The new data, presented today at a conference in South Africa, show the vaccine is what researchers consider modestly effective, although immunity decreases slightly over time. But the vaccine's developers emphasize that it still prevents a lot of cases. Dr. David Kaslow is with the PATH Malaria Vaccine Initiative, a study sponsor.
DR. DAVID KASLOW: Nine hundred and forty-one cases prevented on average for, you know, every thousand young children vaccinated with RTSS, suggests that it has potential for impact; you know, pretty big public health impact. Those are some pretty big numbers of cases averted.
KNOX: Now, 940 cases of malaria prevented out of every thousand kids vaccinated sounds like the vaccine prevents more than nine out of 10 cases. But actually, it's more like one out of two because many African kids get malaria more than once a year. The new data add to results released last year, which gave the first indication the vaccine has limited effectiveness. But Dr. Moncef Slaoui of GlaxoSmithKline, the main sponsor, says even a vaccine of modest effectiveness can have a big impact because malaria is such a huge problem in Africa.
DR. MONCEF SLAOUI: Malaria in sub-Saharan Africa kills around 600,000 children every year, which is an enormous number.
KNOX: The project couldn't demonstrate the vaccine's impact on malaria deaths. That's because children in the study all got the very best treatment, so very few died of the disease. But those who got the vaccine were 36 percent less likely to get severe malaria.
SLAOUI: This vaccine, I believe, over time, will demonstrate in real life, in real use in the field, a very significant efficacy against death resulting from malaria infection. We're talking about very large numbers prevented.
KNOX: But everybody in the field acknowledges that it's not going to be easy to decide how to use the RTSS vaccine. The new data show that 18 months after vaccination, it's 46 percent effective in children immunized between 5 and 17 months of age. For infants, it was only 27 percent effective. Work is underway to see if a booster shot can raise those rates.
Dr. Johanna Daily, of Einstein Medical College, says the results are disappointing.
DR. JOHNANNA DAILY: There's no question everybody would want a higher efficacy on this vaccine. Standard vaccines have over 80 - sometimes 90 - percent efficacy, to protect from other infections. But malaria has always been such a challenge. And we may not ever get those levels.
KNOX: Even when people get infected with malaria - the most effective form of immunization - protection against future infection is far from complete.
DAILY: So it's hard to maybe improve upon nature. So perhaps hoping for a more efficacious vaccine is unlikely and therefore, this would be the thing to go with.
KNOX: Something like 20 other malaria vaccines are in the pipeline. But it's going to be awhile before anyone knows if they'll be more effective than RTSS. GlaxoSmithKline says it will ask European drug regulators next year to approve the vaccine. If they do, the World Health Organization will consider - probably in 2015 - whether to recommend its use.
Daily says malaria vaccine will have to compete with other measures, such as insecticide-treated bed nets to keep malaria-infected mosquitoes from sleeping children.
DAILY: I think it's going to be a very tough question. Each country is going to have a pot of money, and they're going to have to decide how to spend it. Should it go to vaccine? Should it go to bed nets? Should it go to diagnosis? Should it go to community health workers? Each minister of health can decide is this something they want to put their money towards.
KNOX: Glaxo has pledged to keep the cost of the vaccine low. It won't be pennies per dose, the company says; more likely, a few dollars.
Richard Knox, NPR News.
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