COVID-19 reinfections probably rare, according to Italian study

COVID-19 infection was 94% less likely in people previously infected than in those never infected, according to a research letter late last week in JAMA Internal Medicine. However, the researchers note, their study concluded before COVID-19 variants became dominant.

The researchers followed 1,579 COVID-positive patients and 13,496 COVID-negative patients who received reverse transcription-polymerase chain reaction (RT-PCR) diagnoses from February to July 2020 in Lombardy, Italy. After an average follow-up time of 280 days (end date, Feb 28, 2021), 5 previously COVID-infected patients tested positive again via RT-PCR (0.3%), and 528 people were infected for the first time (3.9%).

The hazard ratio for reinfection compared with initial infection was 0.06 (95% confidence interval, 0.05 to 0.08). Incidence density was 1.0 per 100,000 person days for those with a prior infection and 15.1 for those without.

Patients were a median age of 59, and most were older or from the industrial area of Legnano. Reinfection was defined as a second positive RT-PCR test at least 90 days from the first positive diagnosis and with at least two consecutive negative diagnoses in between.

"Because it is likely that immunization plus history of natural infection is better protection than natural infection alone, all persons should be encouraged to get vaccinated even if they have been previously infected with SARS-CoV-2," adds Mitchell H. Katz, MD, in an editor's note.
May 28 JAMA Intern Med study and editor's note

Previous COVID-19 linked to risk of adverse events post-vaccination

An increased risk of adverse events after the first Pfizer/BioNTech COVID-vaccine dose was associated with previous COVID-19 infection, according to a letter to the editor late last week in the Journal of Infection.

The researchers surveyed 974 UK healthcare workers (mean age, 48.9 years) who received their first dose of the Pfizer vaccine. One in four (27.2%) had a previous positive PCR or antibody test result, and 30 of them said they were experiencing long COVID (median duration, 9.3 months).

Female sex and younger age were associated with increased risk of COVID-19 vaccination adverse events, but data also showed that those with previous COVID infections were associated with more vaccine symptoms (1.61 vs 0.89) and vaccine symptom severity (2.7 vs 1.5 symptom-days) after adjustments were made for age and sex. The most common symptoms were fever, fatigue, muscle pain, joint pain, and lymph node pathology. Long COVID-19 was not linked with an increase in adverse events post-vaccination.

"Importantly, among those with prior COVID-19, there was no significant relationship between illness-vaccine time interval and other composite score [of symptom nature and severity]," write the researchers, "nor any difference in mean time interval based on presence of any of the symptoms."
May 29 J Infect study

First human H10N3 avian flu case detected in China

China's National Health Committee (NHC) today reported the first known human H10N3 avian influenza case, which involves a 41-year-old man who sought care on Apr 28 for symptoms, including fever, that began a few days earlier.

In a statement, the NHC said his condition is stable and he is ready to be discharged from the hospital. Sequencing by the Chinese Center for Disease Control detected H10N3. An analysis found that the virus has an avian origin and has low pathogenicity for poultry.

Contact monitoring found no other cases, and the report did not note the source of the man's infection. Officials said the epidemic risk is low and advised people to avoid contact with sick or dead poultry and to wear a mask when experiencing fever and respiratory symptoms.

Filip Claes, PhD, a lab coordinator with the United Nations Food and Agriculture Organization (FAO) told Reuters that H10N3 strain isn't very common and has previously been found in wild birds and waterfowl in Asia and a few parts of North America, but not in poultry.
Jun 1 NHC statement
Jun 1 Reuters story

Minnesota announces farmed deer movement ban due to CWD

The Minnesota Department of Natural Resources (DNR) today announced a temporary ban on the movement of farmed deer across the state, following the discovery of chronic wasting disease (CWD) last week at a farm in Beltrami County.

The ban takes effect today and will last through Jul 31, the DNR said. The temporary ban will allow state officials to detect any connections between CWD discovered in Beltrami County and other deer herds across the state.

"This is a serious disease that poses a growing threat to Minnesota's wild deer, and our actions must reflect that," said DNR Commissioner Sarah Strommen in a press release. "The CWD detections at the Beltrami County farm, its connections to other farms in the state and the additional contamination outside of the farm, pose a risk to wild deer that requires emergency action."

Last week the state announced 13 deer tested positive for the fatal prion disease in a herd of 55 deer in Beltrami County.

CWD was first detected in Minnesota in 2002, and since then the DNR has tested more than 90,000 wild deer in the state, with 115 confirmed positive.
Jun 1 Minnesota DNR press release