Researchers identify two novel SARS-CoV-2 strains most closely related to variants circulating in humans more than 2 years earlier on two mink farms in Poland, the possible result of long-term, undetected circulation in the animals.

For the study, published yesterday in Eurosurveillance, a team led by researchers at the National Veterinary Research Institute in Pulawy, Poland, conducted follow-up SARS-CoV-2 testing from November 2022 to January 2023.

SARS-CoV-2 monitoring on Polish mink farms began in May 2020. Starting in December 2021, all Polish mink farms were monitored when mink showed signs of disease or died in higher-than-expected numbers.

In January 2021, the first farm tested positive, with another 13 farms following suit by July 2022. Four different SARS-CoV-2 variants belonging to eight lineages were identified: B.1.1, B.1.617.2 (Delta), B.1.1.7 (Alpha), and BA.2 (Omicron). Three more mink farms tested positive from September 2022 to January 2023 in the same area.

Routine surveillance needed

On two farms, the researchers uncovered two novel SARS-CoV-2 variants most closely related to the B.1.1.307 strain that circulated in humans in late 2020 and early 2021. The new variants, however, had at least 40 polymorphisms, which the authors said suggests that they originated in an unknown or undetected animal reservoir. The mink did not show symptoms.

It seems that relying only on passive surveillance in response to symptomatic outbreaks could result in many cases being overlooked.

All farm workers and the owners' family members tested negative for COVID-19, meaning that it is unlikely that a chronic viral shedder spread the virus to the mink, but antibody testing wasn't performed, so they may have been previously infected. All farms were surrounded by a concrete barrier, but the introduction of wildlife via tall trees surrounding the barrier or by wild martens or birds could not be ruled out. Feral cat droppings tested negative for SARS-CoV-2.

The researchers noted that the circulation of SARS-CoV-2 in humans and susceptible wildlife at farms carries the risk of viral spillover and the establishment of novel wildlife reservoirs. "It seems that relying only on passive surveillance in response to symptomatic outbreaks could result in many cases being overlooked," they wrote.

Today in Pediatrics researchers published the safety data of the Pfizer-BioNTech (BNT-162b2) COVID-19 vaccine in adolescents ages 12 to 17 years. After 1 year, very few serious adverse events were reported, and instances of myocarditis (inflammation of heart muscle) were lower than initially reported.

The study was conducted using data from two US vaccine safety monitoring systems: v-safe, a voluntary smartphone-based system that monitors reactions and health impacts, and the Vaccine Adverse Event Reporting System (VAERS), the national spontaneous reporting system, the authors said.

The Pfizer two-dose regimen was approved for use in teens in May 2021. From May 2021 to May 2022, 15,493,807 adolescents ages 12 to 17 years received at least one primary dose of BNT-162b2, and 172,032 (1.1%) enrolled in v-safe. The median age of participants in v-safe was 16 years, 54.6% were girls, 62.7% were White, and 73.4% were non-Hispanic or non-Latino.

Most adverse events were mild; among events reported to VAERS, 91.5% were nonserious. Among adverse events of interest, the authors verified 40 cases of multisystem inflammation syndrome in children (1.2 cases per million vaccinations), of which 34 (85%) had evidence of prior COVID-19 infection. They also confirmed 570 cases of myocarditis (17.7 cases per million vaccinations), 77% of which involved symptom resolution at the time of report.

The risk of cardiac disease after COVID-19 infection may be two- to sixfold higher than after vaccination.

"The myocarditis reporting rate was lower for boys ages 12 to 15 years (48.3 cases per million second doses administered) than boys ages 16 to 17 years (84.0 cases per million second doses). These observations are consistent with previous findings that the peak risk group is [in] boys ages 16 to 17 years, although our myocarditis reporting rates are lower than those in early reports," the authors said.

The authors conclude that the vaccine is safe for this age-group, noting that the risk of cardiac disease after COVID-19 infection may be two- to sixfold higher than after vaccination.

One country—Mozambique—reported more polio cases this week, according to the latest weekly update from the Global Polio Eradication Initiative (GPEI).

Mozambique reported three circulating vaccine-derived poliovirus type 1 (cVDPV1) cases this week, all in Zambezia province. The cases were added to its 2022 total, which is now 22.

WHO details cVDPV2 situations in Burundi, Indonesia

In other developments, the World Health Organization (WHO) this week posted updates on circulating vaccine-derived poliovirus type 2 (cVDPV2) situations in Burundi and Indonesia.

The case in Burundi was first reported in the middle of March, and it marked the first instances of cVDPV2 linked to the novel oral poliovirus type 2 since the vaccine was introduced in March 2021. The WHO said the unvaccinated 4-year-old boy's paralysis symptoms began on Nov 24.

Genetic analysis suggests the virus is linked to a new cVDPV2 emergence from the Democratic Republic of the Congo (DRC). An investigation found that polio vaccine coverage was lower in the region where the boy lived compared to the rest of Burundi. Supplemental vaccination campaigns are planned for both Burundi and the DRC in May.

In Indonesia, an outbreak has been under way since 2022. Another paralysis case was detected in March in an unvaccinated 2-year-old girl from West Java province, bringing the country's cVDPV2 total to four, with the earlier three from Aceh province.

The WHO said genetic analysis from the West Java case shows the virus is related to the Aceh virus, but has enough changes to suggest the possibility of missed transmission.