‘Herd immunity’ hurdle
Mass immunizations against Ebola offer little promise of success
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On the heels of the World Health Organization’s announcement of an Ebola outbreak in the Democratic Republic of Congo, a new research study cast doubt on the ability of mass vaccination campaigns to prevent such Ebola outbreaks in the future.
Since April, Congo’s Équateur province has reported 49 likely Ebola cases, including 27 deaths and 28 confirmed cases as of May 22. With memories of the West Africa Ebola epidemic that claimed the lives of 11,310 people a few years ago, WHO has shipped several thousand doses of an experimental vaccine into Congo, meant for health workers and anyone else in immediate contact with Ebola patients.
A larger, mass vaccination campaign to prevent widespread transmission would likely be ineffective, according to the study conducted by England’s University of Kent and published May 9 in Frontiers in Immunology.
Each Ebola patient, on average, infects at least four people in the early stages of the disease. According to the researchers’ analysis, the rapid spread of the virus means 80 percent of the population would need immunization to achieve “herd immunity” and prevent widespread transmission, likely an unachievable number.
In a vaccination trial during the 2014 Ebola outbreak, health professionals could vaccinate only 49 percent of the contacts of infected individuals. Thirty-four percent refused vaccination, and health issues such as HIV and cancer prevented many others from receiving immunization.
To date, no FDA-approved Ebola vaccine exists, and none of the experimental vaccines offer protection against all four types of life-threatening Ebola viruses. Furthermore, researchers do not know if the current vaccines can provide the long-term protection needed to defend against a virus with which humans repeatedly come into contact through animals.
Vaccination campaigns in rural areas of countries like Congo are difficult due to transportation problems, lack of equipment and trained medical personnel, and cultural and language barriers.
The researchers concluded that targeted immunization programs—focused exclusively on healthcare workers and other contacts of infected persons—remain the best vaccine strategy against Ebola for now.
Researchers at the University of California, San Diego, recently discovered they could use a beam of light to control heart cells growing in a lab dish. By varying the light’s intensity, the scientists varied the beating rate of the cells.
The secret, they said, is growing the cells on electrically conductive graphene rather than the usual plastic or glass lab dishes. “In your body, you don’t see many surfaces acting like plastic or glass,” study co-leader Alex Savchenko said in a statement. “Instead, we’re conductive. Our hearts are extremely good at conducting electricity.”
The researchers discovered they could control heart activity in living zebra fish embryos using light and dispersed graphene. The method may aid the development of targeted drugs with fewer side effects, such as those that kill cancer but do not damage healthy cells. It could also help researchers create better medical devices, such as light-controlled pacemakers (Science Advances, May 18). —J.B.
To trace a killer
In the past 40 years a deadly fungal disease called chytridiomycosis has wiped out 200 species of frogs and other amphibians globally. But for decades scientists couldn’t locate the original source of the chytrid fungus. Now, with the help of recent advances in genome sequencing, disease experts at Imperial College London have compared the full genomes of 177 samples of the fungus from six continents. Their May 11 study in Science indicates the pathogen likely originated on the Korean Peninsula 50 to 200 years ago and spread around the world through commercial trade. —J.B.
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