COVID-19 Scan for Oct 18, 2021

SARS-CoV-2 dose and outcomes
Asymptomatic COVID-19 and viral shedding
COVID vaccine cash lotteries

SARS-CoV-2 dose not linked with COVID-19 severity, review says

SARS-CoV-2 dose may affect infection rates, but current data do not show an association between viral dose and COVID-19 severity, according to a review of more than 100 SARS-CoV-2 studies that looks at COVID-19 infectious dose, viral load, severity, and variants.

The aggregated findings were included in Clinical Infectious Diseases late last week and written by US researchers, led by scientists with the University of Minnesota's Center for Infectious Disease Research and Policy, publisher of CIDRAP News.

An infectious dose, the researchers summarized, is often expressed as either the smallest quantity of virus that leads to infection or the median infectious dose. As the review noted, infectious virus is usually not shed beyond 8 to 10 days after symptom onset. Also, in animal studies involving SARS-CoV-2, most infections needed high doses affecting the upper mucosa to result in clinical disease, and infected hamsters and ferrets have been able to transmit the disease to naive animals by contact, contaminating surfaces, and through aerosols.

Other highlighted research includes a 2021 study looking at hospitalizations and severe disease outcomes in healthcare workers that showed a "paucity of evidence" linking dose with severity. Another 2020 study suggested that age was a much greater factor in healthcare workers, The researchers also outline frequently associated health and demographic factors as well as observed differences from variants of concern.

"We found that there is some evidence of a relationship between dose and infection based on animal studies and human epidemiology but minimal data supporting a relationship between dose and disease severity. Instead, host responses and potentially viral genotype primarily determine disease outcomes," the researchers write.

"Non-pharmaceutical interventions may limit the inoculum dose from an exposure, thereby reducing the risk of infection, but they are unlikely to individually have an impact on COVID-19 severity."
Oct 15 Clin Infect Dis paper


Asymptomatic COVID-19 may significantly contribute to transmission

Seventy-five percent of asymptomatic COVID-19 outpatients had mean to high RNA viral loads, and 50.6% of those whose samples were tested with culture assays had live cultures, according to a study today in Scientific Reports.

The researchers say this indicates that COVID-19 asymptomatic adult outpatients could play a large role in perpetuating COVID outbreaks. The study was conducted before the much more transmissible Delta (B1617.2) variant was circulating.

The study involved 17,911 French adults who were tested for COVID-19 in the Champagne-Ardenne area from Jun 4 to Sep 20, 2020. About 2.8% were positive based on samples from the upper respiratory tract, and 36.3% (180) of those people had asymptomatic cases. While asymptomatic patients had more low viral loads than symptomatic patients (25% vs 11.7% had cycle threshold [Ct] values 30 or higher), 75% of asymptomatic patients still had high viral loads, with a median value slightly higher than those in symptomatic patients (21.60 vs 22.57 Ct among all values below 30, P = 0.029).

In addition, 83 asymptomatic patients had their samples tested by the culture assay protocol: 50.6% were positive.

"Only the viral loads of patients who were sampled between 8 and 28 days after symptom onset were significantly lower than those of asymptomatic patients (P=0.041)," the researchers write, noting that as expected, viral RNA loads appeared to be highest during or before symptom onset. Still, they conclude, "Our findings indicate that COVID-19 asymptomatic adult outpatients are significant viable SARS-CoV-2 shedders in their upper respiratory tract, playing a major potential role as SARS-CoV-2 transmitters in various epidemiological transmission chains, promoting COVID-19 resurgence in populations."

Of the COVID-19 positive study participants, 66.0% were women, and the mean age was 41.8 years. In the asymptomatic group, 60.1% were women, and the mean age was 32.3 years. The overall median Ct value was 23.57 cycles.
Oct 18 Sci Rep study


COVID-19 vaccine lotteries did not increase uptake, study finds

COVID-19 vaccine-related cash drawings in 19 states did not increase uptake, according to a research letter published late last week in JAMA Health Forum.

The researchers looked at daily state-level COVID-19 vaccination data before and after cash drawings announcements, as well as the data from the rest of the US states that didn't have those incentives, from Apr 28 to Jul 1. Vaccination appointments were widely available, and during the study period, 37.2 million first doses of a COVID vaccine were administered in the country, with 19.2 million of those in the states with cash drawings.

Adjusted regression estimated that the cash drawings were associated with –0.06 daily vaccination per 1,000 people (95% confidence interval [CI], –0.43 to 0.30). This finding was supported by the researchers' event-time estimates, which showed no statistical significance using both a conventional and novel model that better accounted for staggered announcements.

"With the upper bound of the 95% CI for the first-dose estimate of 0.30 daily vaccinations per 1000 population, we can rule out fairly small associations between lottery announcements and vaccinations," the researchers write. "If the cash-drawing announcements had been associated with 70% of US adults receiving a first vaccine dose by July 4 (President Biden's stated goal), we would have expected an estimate of approximately 1.22 daily vaccinations per 1000 population."

The researchers speculate that the null impact could be because lottery-style cash drawings weren't assured-enough incentives or because the campaigns didn't have enough vaccination-related information in addition to the prize announcement.
Oct 15 JAMA Health Forum study

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