Coronavirus Research Tracking - 28 August
Reports of re-infection, convalescent plasma therapy, mask wearing and distancing, infections in children, and risks for more severe Covid-19 outcomes.
In this week’s Research Tracker we look at re-infection, convalescent plasma therapy, face masks and prosocial behaviours, infection levels in children, and factors influencing more severe outcomes.
The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre.
Re-infection
A paper on a Hong Kong man who became infected with a second lineage of SARS-CoV-2 has been published in Clinical Infectious Diseases. It reports that the man became re-infected while overseas 142 days (7 months) after a mild infection in March.
Comparison of the genome sequences of the viruses from the two infections demonstrated that they were different, indicating separate infections. The man was asymptomatic the second time and produced relatively low levels of antibodies. Antibodies were not found when he was tested during his first infection.
Some scientists have criticised some of the media coverage and interpretation of the significance of this result. Re-infections of human coronaviruses are known, and it does not undermine a vaccination strategy.
The Science Media Centre has Expert Reaction to the initial media reports of re-infection.
Two other cases of possible re-infection have since been reported in the Netherlands and Belgium, but details are limited.
Convalescent Plasma
Another report that received significant media attention this week was on the effects of using plasma from recovering Covid-19 patients on others with Covid-19. The, as yet not peer reviewed, paper compared mortality in over 35,000 patients who received plasma. Relative mortality at seven and 30 days was lower in patients who received plasma earlier (within 3 days of showing symptoms), and with higher levels of IgG antibodies.
However, this was not a randomised controlled trial so does not provide clear evidence of safety and effectiveness. Scientific American discusses the limitations of current research on convalescent plasma.
Some of the data in the paper prompted the FDA to issue an emergency use authorisation for convalescent plasma. The New York Times covers scientists' critiques to the FDA’s decision.
Coughs and masks
A study published in Physic of Fluids analysed aerosol droplet spread from voluntary coughs with and without face or mouth coverings. Without masks droplets may travel up to 3 metres horizontally. A surgical mask can reduce that down to 0.5-1.5 metres, while N95 masks limited spread to 0.25 metres. The researchers noted, though, that tests involving more people are needed to better understand the effectiveness of different types of face coverings.
A paper in the Journal of General Internal Medicine reviewing theory and evidence concludes that mask wearing reduces the viral dose the wearer inhales. This, they propose, is likely to reduce the likelihood of infection and severity of disease. Covid-19 data isn’t available to confirm, or refute, this.
Clear communications necessary if mandatory mask wearing required
A German study, published in the Proceedings of the National Academy of Sciences, surveyed people’s behaviour and attitudes toward mask wearing. It found that those who report that they wear, or support, masks exhibited more “prosocial behaviours” than those who didn’t. Prosocial behaviours include hand washing and physical distancing.
That’s probably not a surprising discovery. But the authors note that widespread mask wearing is required to have an impact on viral spread. If mask wearing is to be mandatory they recommend that communications need to highlight both the benefits to individuals as well as the benefits of a mandatory policy (such as fairness).
A more nuanced approach to physical distancing is suggested
A paper in the British Medical Journal notes that the evidence for 2 metre physical separation to reduce infection risks is based on outdated science. It suggests taking more account of environmental and behavioural factors that influence infection risks. The authors propose a matrix of separation distances that considers crowding, mask wearing, ventilation and exposure time.
However, they don’t discuss the challenges of communicating, remembering and enforcing a more complex set of rules.
Teachers may be more at risk of infection than students in schools
A study of 30 school outbreaks in England found that teachers rather than students were more likely to become infected. Most of the infected children were asymptomatic. The report, published by Public Health England, recommends that greater precautions need to be taken by teachers. One limitation of the study was that many secondary schools were closed at the time.
Children can have high levels of the virus, but not show symptoms
Research published in JAMA Pediatrics found that children under five can have higher levels of the virus in their nose and throat than adults. Older children can harbour similar levels as adults. The study didn’t test the infectivity of younger and older children.
A separate study in JAMA Pediatrics found that infected children (with a mean age of 10 years old) often had high levels of the virus, but only about half had a fever, and many had non-specific or no symptoms. This study, though, didn’t find a difference between age and the amount of virus present.
Risk factors associated with more serious Covid-19
An article in Scientific American summarises the main factors that influence severity of outcomes. These are:
Age. Immune responsiveness decreases with age.
Sex. Males tend to have more severe outcomes. There are three hypotheses that may help explain gender differences.
Genetic variation. Individual variation may influence, for example, cytokine expression.
Pre-existing health conditions may weaken immune responses or worsen Covid-19 conditions.
Inequality & racism, which influence exposure risks, along with access to, affordability and quality of healthcare.
A study just published in Nature found that immune responses to moderate Covid-19 differed between men and women. Male patients had higher levels of some pro-inflammatory interleukins, while women had better T cell activation, suggesting a more balanced immune response. The causes for the differences are uncertain. The researchers suggest that clinicians should more carefully consider the sex of Covid-19 patients before deciding on treatments.
In research published in Annals of Internal Medicine patients with extreme obesity had more than two times the risk of death from Covid-19 than those with lower body mass indices. The association between mortality and high BMI was strongest in younger adults and male patients. Obesity-related co-morbidities had little influence.