News Scan for Nov 15, 2019

Latest polio cases
Vaccinia virus in Colombia
Flu vaccine and childhood imprinting

Pakistan, several African countries report vaccine-derived polio cases

Pakistan, Nigeria, the Democratic Republic of the Congo (DRC), and Angola each reported new cases of vaccine-derived polio, according to the latest weekly update today from the Global Polio Eradication Initiative (GPEI), and Pakistan also confirmed cases involving the wild-type virus.

In Pakistan, two wild poliovirus type 1 (WPV1) cases raise the country's total this year to 82, a significant increase over last year's total of 12. The new case-patients are both from Lakki Marwat in Khyber Pakhtunkhwa province and experienced paralysis onset on Oct 21. Pakistan officials also noted seven cases of circulating vaccine-derived poliovirus type 2 (cVPDV2) polio, its first involving vaccine-derived viruses. Four of the cVPDV2 cases are in Gilgit Batistan province, with two in Khyber Pakhtunkhwa province and one in Islamabad.

In today's Morbidity and Mortality Weekly Reports (MMWR), researchers said the sharp rise of polio activity in Pakistan this year is due to a combination of factors, including vaccine refusal and chronically missed children. They also note WPV1 has been widely detected in sewage across the country.

"The number of cases in 2019 to date has increased approximately fifteen-fold from the same period in 2018, and the geographic distribution of WPV1-positive environmental surveillance specimens has expanded beyond the core reservoirs," the authors write.

In Nigeria, officials recorded one case of circulating vaccine-derived poliovirus type 2 (cVPDV2) in Kogi province. This is the 17th cVPDV2 case recorded in Nigeria this year.

Eight cases of cVDPV2 were recorded in the DRC this past week, raising the year's total to 42 cVDPV2 cases in 2019, compared with 20 in all of 2018. In Angola, 3 new cVDPV2 lift the country’s 2019 total to 41 cVDPV2 cases from seven outbreaks.

In a separate MMWR report on vaccine-derived cases, authors say between January 2018 and January 2019, 25 cVDPV2 outbreaks were reported in 13 countries, 12 of which were in Africa. In general, the number of cVDPV outbreaks detected worldwide increased from nine in six countries in 2017-2018, to 29 in 15 countries in 2018-2019.
Nov 15 GPEI update
Nov 15 MMWR vaccine-derived polio report
Nov 15 MMWR Pakistan


Seroprevalence study builds case for zoonotic vaccinia in Colombia

Vaccina virus (VACV) appears to be an emerging zoonotic disease in Colombia, according to results from a seroprevalence study in farmworkers and household members in two of the country's departments. A team from the US Centers for Disease Control and Prevention (CDC) and their colleagues in Colombia reported its findings yesterday in Emerging Infectious Diseases.

VACV infections were identified in farm workers in Caqueta and Cundinamarca departments in 2014 and 2015. The orthopox virus (OPXV) is used in smallpox vaccine and has triggered sporadic bovine and human outbreaks in Brazil and India. Experts have debated whether VACV escaped into animals as the result of human vaccination efforts, with recent studies suggesting endemic spread in Brazil. No reservoir has been confirmed, but data suggest that rodents might harbor the virus.

To help better understand the scope of the disease in Colombia, researchers obtained blood samples from 134 farm workers and household members from 56 farms in Cundinamarca department in August and September of 2016.

Lab tests revealed that 52% of farm workers has OPXV antibodies, but when the investigators excluded those who would have been eligible for smallpox vaccination, the number decreased to 31%. Risk factors linked to testing seropositive included city of residence, age, smallpox vaccination scar, time working on a farm, and working with animals that had vaccina-like lesions. The authors wrote that they were surprised that household transmission didn't seem to be a mechanism for virus spread. They also said consuming unpasteurized dairy products didn't seem to be linked to virus spread.

Seropositivity was linked to a history of clinical symptoms in 13% of the study participants, suggesting a substantial disease burden, the team wrote. "This outbreak investigation reveals that VACV is likely to become an increasingly important zoonosis in this part of the world, either through independent emergence events or expanding reservoir habitats against a backdrop of waning immunity," they added.
Nov 14 Emerg Infect Dis study


Study hints at imprinting interference against H3N2 flu in some vaccinated adults

Vaccination against flu in Canada's 2018-19 season appears to have made adults ages 35 to 54 more vulnerable to the disease because of a negative impact of a drifted H3N2 virus on people who were first exposed to H3N2 flu as children in the decades following 1968. Researchers with the Canadian Sentinel Practitioner Surveillance Network described their findings yesterday in Eurosurveillance.

For the study, the scientists assessed flu vaccine effectiveness (VE) against H3N2 by a test-negative design, looking for any differences between clades 3C.2a1b, the one included in the vaccine, and 3C.3a, which was the drifted circulating strain.

Overall, VE against H3N2 was 17% (95% confidence interval [CI], −13% to 39%). Against the virus similar to the vaccine strain, VE was higher, at 27% (95% CI, −7% to 50%), and against the drifted strain, VE was much lower, at -32% (95% CI, −119% to 21%). In people ages 20 to 65, VE was -7% overall (95% CI, −56% to 26%), 6% (95% CI, −49% to 41%) against the matched strain, and -96% (95% CI, −277% to −2%) against the drifted strain. The CI for all these factors, however, reflect no significant protection.

The authors reported a pronounced negative dip in VE in people ages 35 to 54, who had a more than four times greater odds of getting sick with medically attended flu compared to their unvaccinated peers.

Vaccine mismatch may have negatively interacted with imprinted immunity, and the mechanisms behind the immunological interference require further study, the researchers wrote. They note that surveillance system in Europe and the United States picked up similar signals, and their study included a hypothesis box to spur further discussion by the scientific community.
Nov 14 Eurosurveill report

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