News Scan for Sep 20, 2019

Polio in Philippines, Africa
Waning yellow fever vaccine response

Philippines reports 2nd polio case; more cases confirmed in Africa

Health officials in the Philippines confirmed a second polio case today, a day after declaring an outbreak based on reports of an illness involving circulating vaccine-derived poliovirus type 2 (cVDPV2) in Lanao del Sur province and environmental detections in Manila and Davao region. The polio cases are the country's first in nearly two decades.

The second case involves a 5-year-old boy from Laguna province, which is south of Manila, the Associated Press (AP) reported today, based on statements from the Philippines health secretary.

In a statement today, the Philippines Department of Health said it signed a memorandum of understanding with Rotary International to heighten polio awareness and initiate a vaccine campaign because of the cases. It added that a 2018 assessment found that 12 of the country's 17 regions were at risk for polio reemergence, including National Capital region, where oral polio vaccine coverage declined steadily from 77.25% in 2016 to 23.45% in the second quarter of 2019.

In other polio developments, the Global Polio Eradication Initiative (GPEI) in its latest weekly update today noted the reemergence of polio in the Philippines and reported new cVDPV2 cases in Nigeria and Angola.

Nigeria has one new case, which involves a patient from Koji province whose paralysis symptoms began on Aug 8. The country has now reported 16 cases for the year.

Meanwhile, Angola reported 7 new cases, 4 in two different districts in Huambo province, and 1 each from Lunda Norte, Bie, and Luanda provinces. Paralysis onsets ranged from Jun 7 to Aug 14. Angola now has 15 cases for the year, which are part of five different outbreaks.
Sep 20 AP story
Sep 20 Philippines Department of Health press release
Sep 20 GPEI update


Study: Infants dosed with yellow fever vaccine have waning protection

A new study of two cohorts of children who received a yellow fever vaccine between 9 and12 months of age, found protective antibodies dropped significantly within 2 to 5 years after vaccination. The study appeared yesterday in The Lancet Infectious Diseases and may offer new evidence of the necessity of yellow fever booster doses.

One dose of the yellow fever vaccine is supposed to offer lifelong immunity to adults and children over the age of 2. In countries where the disease is endemic, vaccination is often recommend to infants.

In the study, researchers included two cohorts of children from Ghana (436 children) and Mali (587 children) who were vaccinated against yellow fever before they turned 1, with a mean age at vaccination of 9 months. Antibodies were measured 4 weeks after the vaccine administration and then through several years of follow-up. Tests showed that antibody levels fell sharply within a few years in both groups.

In the Ghanaian cohort, by 2.5 years after vaccination, only 27.8% of children continued to have a strong immune response, which the authors defined as having specific antibodies at the concentration 0.5 International Units per milliliter or more. In the cohort from Mali, only 50.4% of the children had that level of antibodies 4.5 years after vaccination.

"Our study shows that the long-term outcome of the vaccination of 9-month-old infants against yellow fever is unsatisfactory and argues for the one-dose-for-life recommendation to be reconsidered for this population in endemic countries," the authors concluded. They add, "The long-term decline of humoral immunity suggests that a single dose of the vaccine, administered at 9 months of age, might not achieve a population immunity protective against yellow fever epidemics."

In an accompanying commentary in the same journal, a Brazilian and US expert write, "Equivalent studies will also be needed in some of the other 40 countries where yellow fever is endemic, assessing all four [World Health Organization] prequalified vaccines, to provide more information on whether booster doses are needed for children and, consequently, whether modifications to the current immunisation regimen are necessary."
Sep 19 Lancet Infect Dis
Sep 18 Lancet Infect Dis commentary

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