8 October : Dense cities should brace for long coronavirus outbreaks
The new coronavirus tears through areas where residents generally keep to their own small, close-knit communities. But the virus takes its time spreading in crowded cities where residents of different neighbourhoods tend to intermingle, ultimately infecting more people than in the relatively isolated areas.
Moritz Kraemer at the University of Oxford, UK, and his colleagues modelled the spread of SARS-CoV-2 through communities of various sizes and population densities(B. Rader et al. Nature Med. https://doi.org/fcjk; 2020). The researchers validated their model by comparing its output with known data on individual movements and infection rates in crowded Chinese cities such as Wuhan and less densely packed provinces in Italy.
The team's model predicts relatively short, intense spikes in COVID-19 cases in relatively uncrowded cities where residents stick to their own neighbourhoods rather than mingling freely. In crowded cities, however, people are more likely to have to cope with outbreaks that last longer than do those in the countryside.
The researchers applied their model to 310 cities worldwide, and predict that those with relatively even population distributions, such as Ulaanbaatar in Mongolia, could expect a short-term explosion in cases. But more densely settled urban centres, such as Madrid, can expect more protracted outbreaks.
6 October : Teenager spreads coronavirus on family holiday
A 13-year-old girl gave the new coronavirus to her grandparents and 9 other relatives who occupied the same holiday house for up to 3 and a half weeks, confirming that adolescents can seed clusters of COVID-19 cases.
According to an investigation by Noah Schwartz at the Centers for Disease Control and Prevention in Atlanta, Georgia, and his colleagues, the girl was exposed to SARS-CoV-2 in June. After a rapid test suggested that she was not infected, she joined 13 family members for an extended stay in a 5-bedroom house (N. G. Schwartz et al. Morb. Mortal. Wkly Rep. https://doi.org/10.15585/mmwr.mm6940e2; 2020). Family members neither wore masks nor maintained distance from each other.
Twelve people in the house, including the teenage girl, developed COVID-19 symptoms and either tested positive for the coronavirus or were classified as probable cases. Six other relatives visited those staying in the house but remained outdoors and kept their distance. Of those six, all four who took a coronavirus test tested negative, and none fell ill.
5 October : Massive contact-tracing effort in India reveals striking trends
The patterns of infections and deaths caused by the new coronavirus differ starkly between resource-poor settings and wealthier places, according to the largest contact-tracing study conducted so far, carried out using data from India.
Joseph Lewnard at the University of California, Berkeley, and his colleagues analysed data from almost 85,000 people with COVID-19, as well as their close contacts who numbered nearly 600,000 in the states of Tamil Nadu and Andhra Pradesh (R. Laxminarayan et al. Science https://doi.org/10.1126/science.abd7672; 2020).
The incidence of COVID-19 in the two states declines steadily with age for people aged 40 and older in contrast to the United States, where incidence climbs with age from age 65. Mortality rates for those aged 75 and above were markedly lower in India than in the United States perhaps, the researchers say, because people in India who live to old age tend to be relatively wealthy compared with those who die younger.
The study also found that people were most likely to infect others within their own age group. This is especially true of children, suggesting that socialising among kids could contribute to viral spread.
2 October : The immune trait that could allow viral reinfection
Waning antibody levels or a poorly developed immune response to SARS-CoV-2 could put people at risk of reinfection, one case suggests.
In March, a care-home resident in their sixties developed severe pneumonia and tested positive for the new coronavirus. The individual spent more than one month in hospital before testing negative. In July, the individual tested positive again, with milder symptoms of coughing and shortness of breath.
The team also measured the individual's neutralizing antibodies, which protect cells against infection. The person had lower levels of these potent antibodies against the version of SARS-CoV-2 that caused the first infection than against the version that caused the second infection.
The researchers say that these measurements provide a useful benchmark for antibody levels that do not protect against reinfection. The research has not yet been peer reviewed.
1 October : A fast-spreading viral variety shows higher infectiousness
Variants of SARS-CoV-2 with a widespread mutation are more infectious in human cells and hamsters, compared with viral variants lacking the change.
In February 2020, researchers examining samples from people with COVID-19 detected a SARS-CoV-2 mutation that alters the amino acid sequence of the virus's spike protein, which the virus uses to infect cells. The amino-acid alteration, known as D614G, became common in Europe, North America and elsewhere in spring 2020, and now nearly all viruses isolated worldwide carry the alteration.
Both teams found that, compared with forms of the virus that lack the mutation, D614G variants replicated more efficiently in cells from human airway tissues. Baric's team also found that D614G variants spread faster between hamsters, which are used to study SARS-CoV-2 transmission. Neither finding has been peer reviewed yet.