Tuesday July 23, 2019

Study: Partial Dose of Yellow Fever Vaccine Provides Protection

A full dose of yellow fever vaccine provides lifelong immunity. Researchers will continue to study how long people who received partial doses are protected

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Yellow fever is a mosquito-borne viral disease found in tropical Africa and South and Central America.
Yellow fever is a mosquito-borne viral disease found in tropical Africa and South and Central America. Wikimedia Commons
  • Yellow fever is a mosquito-borne viral disease
  • Severe cases can cause jaundice and death, but most cases involve fever, muscle pain and vomiting
  • More than 350 people have become infected with yellow fever in Brazil since late last year

When stockpiles of yellow fever vaccine run low, partial doses are effective, according to a new study.

The report on the vaccine, which currently is in short supply, comes as officials in Brazil attempt to contain an outbreak with what they describe as the largest-ever mass vaccination campaign using partial doses.

Yellow fever is a mosquito-borne viral disease found in tropical Africa and South and Central America. Severe cases can cause jaundice and death, but most cases involve fever, muscle pain and vomiting.

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Congo outbreak, experiment

During a major outbreak in the Democratic Republic of the Congo in 2016, the government aimed to prevent the disease from spreading in the capital, Kinshasa. Health officials launched a mass vaccination campaign targeting 7.6 million people.

But the outbreak had depleted vaccine stockpiles. Hoping to stretch the available supply, the World Health Organization reviewed the small number of available studies on using reduced doses and recommended using one-fifth of a dose per person.

It seemed to work.

Health officials have launched a campaign targeting nearly 24 million people with a one-fifth dose of the vaccine. Wikimedia Commons
Health officials have launched a campaign targeting nearly 24 million people with a one-fifth dose of the vaccine. Wikimedia Commons

Researchers took blood samples from more than 700 people before and after they received the partial dose. In the new study, published in the New England Journal of Medicine, nearly all of those vaccinated with the lower dose developed enough antibodies to the virus to prevent infection.

“That was the encouraging thing, that this can be done as a potential way — when there’s supply limitations on the vaccine — to help potentially control an outbreak,” said study co-author Erin Staples at the U.S. Centers for Disease Control and Prevention.

Hundreds infected

More than 350 people have become infected with yellow fever in Brazil since late last year, and health officials have launched a campaign targeting nearly 24 million people with a one-fifth dose of the vaccine.

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Staples says the new study is good news for controlling outbreaks like Brazil’s in the short term. But, she notes, “We still need some information about how long immunity will last.”

A full dose of yellow fever vaccine provides lifelong immunity. Researchers will continue to study how long people who received partial doses are protected. (VOA)

Next Story

Strains of Malaria Resistant to Two Key Anti-Malarial Medicines Becoming More Dominant in Southeast Asia

Strains of malaria resistant to two key anti-malarial medicines are becoming more dominant in Vietnam

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Malaria, Medicine, Asia
FILE - Children living in the Thai-Myanmar border come to a malaria clinic to get tested in Sai Yoke district, Kanchanaburi province, Thailand, Oct. 26, 2012. VOA

Strains of malaria resistant to two key anti-malarial medicines are becoming more dominant in Vietnam, Laos and northern Thailand after spreading rapidly from Cambodia, scientists warned Monday.

Using genomic surveillance to track the spread of drug-resistant, the scientists found that the strain, known as KEL1/PLA1, has also evolved and picked up new genetic mutations which may make it yet more resistant to drugs.

“We discovered [it] had spread aggressively, replacing local parasites, and had become the dominant strain in Vietnam, Laos and northeastern Thailand,” said Roberto Amato, who worked with a team from Britain’s Wellcome Sanger Institute and Oxford University and Thailand’s Mahidol University.

It is caused by Plasmodium parasites which are carried by mosquitoes and spread through their blood-sucking bites.

Malaria, Medicine, Asia
FILE – Village malaria worker Phoun Sokha, 47, shows his malaria medicine kit at O’treng village on the outskirts of Pailin, Cambodia, Aug. 29, 2009. VOA

Almost 220 million people were infected with malaria in 2017, according to World Health Organization estimates, and the disease killed 400,000 of them. The vast majority of cases and deaths are among babies and children in sub-Saharan Africa.

Malaria can be successfully treated with medicines if it’s caught early enough, but resistance to anti-malarial drugs is growing in many parts of the world, especially in Southeast Asia.

The first-line treatment for malaria in many parts of Asia in the last decade has been a combination of dihydroartemisinin and piperaquine, also known as DHA-PPQ. Researchers found in previous work that a strain of malaria had evolved and spread across Cambodia between 2007 and 2013. This latest research, published in The Lancet Infectious Diseases journal, found it has crossed borders and tightened its grip.

“The speed at which these resistant malaria parasites have spread in Southeast Asia is very worrying,” said Olivo Miotto, who co-led the work.

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“Other drugs may be effective at the moment, but the situation is extremely fragile and this study highlights that urgent action is needed,” he said. (VOA)