Coronavirus Research Tracking - 14 August
Virus lineages in NZ, the types of diagnostics tests, when and where transmission is greatest, and how good are masks
In this week’s Research Tracker we look at papers on the genome sequences of the virus from New Zealand, testing methods & strategies, infections of close contacts, and the effectiveness of face masks.
The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre.
Transmission lineages in New Zealand
Analysis of 649 SARS-CoV-2 genome sequences from New Zealand (not yet peer reviewed) identified 277 separate introductions of the virus. Just over half of these did not lead to infections of other people. 19% of the introductions infected more than one other person, creating a transmission lineage. Larger social gatherings (weddings, conferences, and hospitality-related events) produced the larger transmission lineages.
What types of diagnostic tests are there, and how good are they?
A paper published in iScience reviews the different genetic and antibody tests being used for SARS-CoV-2 infection. It describes how each test works and the evidence for their accuracy and specificity. Some of the newer RNA tests still require further validation, and there can be inconsistent results from different antibody tests.
Areas for test and testing improvements that the authors identify include development of fast & cheap antigen tests and novel biosensor methods, serial tracking of individuals to understand the dynamics of infection, and the development of global testing standards.
Frequent testing and quicker reporting may be more useful than slower more accurate testing
A modelling study (not yet peer reviewed) compared the effectiveness of identifying infections using a very accurate genetic test conducted less frequently with more frequent use of a rapid but less accurate test. It found that rapid detection of outbreaks depends more on frequent testing and rapid reporting of results, with high accuracy having only a marginal effect. The paper concludes that infection surveillance should prioritize accessibility, frequency, and quick reporting. The different strategies haven’t yet been compared in the field.
Asymptomatic and symptomatic people may have similar levels of the virus
Research in South Korea, published in JAMA Internal Medicine, found that the levels of virus in asymptomatic people were similar to those with symptoms. Whether asymptomatic people spread the virus as much as those with symptoms was not evaluated. A caveat of the study is that most of the people tested were young and relatively healthy.
More transmission may occur before symptoms appear
A large study of infection records in China estimated that infectiousness was at its highest one to two days before symptoms appeared. Most transmission events occurred between one week before and one week after symptoms appeared, with 62.5% of transmission events occurring in the pre-symptomatic stage. At least 3.5% of cases appeared to be from asymptomatic individuals. This study hasn’t yet been peer reviewed.
Risk of infection more likely for household contacts
Another study in China of transmission to close contacts found that overall transmission was low (3.7%). Transmission was greatest for household contacts of an infected person (10% became infected). The risk of spreading the virus was greater if the infected person had more severe symptoms. Asymptomatic people had the lowest frequency of spreading the virus. The research has just been published in the Annals of Internal Medicine.
Masks help control infections
A paper published in Nature Communications modelled various mask wearing strategies. It found that mask wearing reduces infections and deaths. Not surprisingly more effective masks and greater mask wearing had the largest impacts. The study also considered if mask supplies were limited. In this case it found that the best strategy is to prioritise distribution of masks to those already infected, along with the elderly and other groups most at risk of serious infection outcomes.
The effectiveness of different masks
More reports are appearing that test how effective different types of masks are.
A study published in Science describes a quick method to test the effectiveness of masks. It tested 15 commonly available face masks or mask-like coverings to determine how effective they were at blocking droplets when speaking. The study was designed to illustrate the technique rather than provide a detailed assessment of the effectiveness of different masks. However, the initial data indicates that mask-like coverings (such as bandanas) do little to prevent droplet spread.
Another study in the USA, published in JAMA Internal Medicine, tested the filtering capacity of a variety of approved and non-approved respirators and face masks used in healthcare facilities. It found that masks not approved (by the CDC or National Institute for Occupational Safety & Health) for healthcare use performed less well compared to approved N95 masks. However, expired N95 masks (nine years old) were still effective at reducing bioaerosol dispersal if they are properly fitted.
The study also found that treating masks with ethanol or vapourised hydrogen peroxide were effective means for cleaning and reusing masks, although care needs to be taken by the wearer to avoid contact with ethanol after treatment. Steam sterilization was not a good method for cleaning masks.
An item on Newsroom summarises some of the science on the use of face masks.