Malaria vaccines reduce cases by 91% as scientists edge closer to AIDS jab
*HIV tests give false negative results if people take controversial preventative drug
Using two experimental anti-malarial vaccines, which work in different ways, can greatly reduce the number of malaria infections in animal studies.Experimental vaccines, which independently achieve 48 per cent and 68 per cent reductions in malaria cases, can achieve 91 per cent reduction when combined.Presently, each vaccine is at a different stage of human trials, and there have not been efforts to combine them. However, a team led by Imperial College London has now tested the effectiveness when using the two types of vaccine together.
The study, published Monday in the journal eLife, used genetically altered mouse parasites that express proteins expressed on the human version of the malaria parasite. The PATH Malaria Vaccine Initiative and the Medical Research Council (MRC), including researchers at Imperial’s MRC Centre for Outbreak Analysis and Modelling, funded the research.Lead researcher, Dr. Andrew Blagborough, from the Department of Life Sciences at Imperial, said: “This is the first direct evidence that combining vaccines of different types significantly improves their efficacy in terms of reducing malarial burden.
“Reaching a potential 91 per cent reduction in cases would have a huge impact on public health because the vaccines could be effective in areas where malaria is more prevalent.”
This comes after research released last April suggested scientists are edging closer to a long-term preventative Human Immuno-deficiency Virus (HIV) vaccine.A single injection protected monkeys against a version of the virus for at least 18 weeks, suggesting the jab could offer people months of immunity, a study by Rockefeller University, New York, found.
Developing such a vaccine is difficult due to HIV ‘hiding’ from people’s immune systems, however, including certain proteins in the injection cause immune cells to recognise parts of the ‘envelope’ that surround the virus, the research adds.According to the researchers, their findings, published in the journal Nature Medicine, ‘lay the groundwork’ for a preventative vaccine that could be given as little as once a year. It is unclear when it may be available.
Also, people taking a controversial preventative Human Immuno-deficiency Virus (HIV) drug could give false negative results for up to seven months, new research suggests.Tests are unable to pick up the virus in those taking Pre Exposure Prophylaxis (PrEP), a United States (US) study found.
Infected people may then have unprotected sex thinking they are HIV free, the researchers warn.PrEP is approved for people at a high risk of HIV infection, such as those with an affected partner.Critics claim it encourages sexual promiscuity, which could increase the transmission of other sexually transmitted infections (STIs).
Meanwhile, malaria is caused by a group of parasites that have a complex life cycle, spending time in the mosquito midgut and salivary glands, in the human liver, and circulating in human blood, where they cause the disease.The team tested two types of vaccines: those that prevent mosquitoes from transferring the parasites, called transmission-blocking vaccines (TBVs), and those that prevent the parasite from infecting the liver, termed pre-erythrocytic vaccines (PEVs).
RTS,S is the world’s first PEV malaria vaccine that has been shown to provide partial protection against malaria in young children by blocking infection of the liver. However, its maximum efficacy is under 50 per cent (that is it reduces cases by around 50 per cent).
There are currently several types of transmission-blocking vaccines in early trials, which are thought to reduce the number of parasites in the mosquito salivary glands. Their efficacy typically ranges from around 50-95 per cent.It has been assumed that combining these vaccines would increase their efficacy, but it has never been tested until now. The team found that when a partially effective PEV was combined with the most effective transmission-blocking vaccine, the efficacy was around 91 per cent.
The team also found that combining any of the two types of vaccines improved efficacy of the mixture more than might be expected from the single efficacy of each vaccine separately.Dr. Morven Roberts, Programme Manager for parasites and neglected tropical diseases at the MRC, said: “While these findings are in the preliminary stages, they’re valuable as they shed light on optimising strategies for preventing malaria. Learning that combining vaccines can dramatically boost efficacy in mice provides another potential tactic for controlling this disease. This is timely research as global health officials work towards WHO targets to eliminate malaria by 2030.”
The team will next study how combined vaccines could work in more complex situations. Blagborough said: “In the real world, the vaccine coverage we can achieve- how many people we can give it to – is important, as are the local levels of transmission, and how prevalent malaria currently is in that area.”We plan to use a combination of rodent experiments and computer modelling to help us estimate effectiveness requirements for future vaccines.”
The efficacy of current lead malaria vaccines is known to reduce over time after vaccines are administered, so the team will also investigate how combined vaccines perform in the long term.What is PrEP? It is the HIV prevention drug that stops 90 per cent of transmission. This drug in particular is fixed-dose combination of two anti-retroviral drugs, tenofovir and FTC, in one pill.
They work together to interfere with an enzyme, which HIV uses to infect new cells, slowing down the virus’s attack or preventing it altogether. The drug is designed for people that have not yet been exposed to the virus to protect themselves against it. Alternatively, people who have been exposed can take PEP (post-exposure prophylaxis), a month-long course of drugs started within 72 hours of exposure.Why does PrEP make HIV tests less accurate? HIV infections cause people’s immune systems to make proteins, known as antibodies that fight the virus.
These antibodies are what HIV tests detect.As PrEP prevents the HIV virus multiplying, it may cause antibody numbers to rise more slowly.This could mean it takes longer for a person to produce a sufficient number of antibodies for a test to detect them. PrEP users are recommended to have HIV tests every three months in case they miss a dose, however, lead author Ivana Parker, from the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, suggests they get tested every four weeks.
The CDC is looking into developing more sensitive HIV tests that detect low antibody levels, the New Scientist reported.How was the research was carried out? The researchers analysed the blood and saliva samples of injecting drug users. The users, from Thailand, were taking PrEP.Results suggest it takes seven months before HIV-related antibodies are detected in saliva tests and three months for blood tests. The findings were presented at an American Society for Microbiology meeting in Atlanta.
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