How did Covid-19 first spread?

It is the dominant view amongst scientists that the SARS-CoV-2 virus, commonly known as Covid-19, emerged naturally in China and made a “zoonotic” jump from animals (most likely bats) to humans. However, since the start of the pandemic, alternative theories have emerged arguing that the virus escaped from a Wuhan laboratory in some sort of accident. These theories, often called “lab leak” theories, have largely been dismissed as lacking in evidence. In May 2021 however, President Biden ordered the US intelligence community to reassess the lab leak possibility. The director-general of the World Health Organization (WHO), Tedros Adhanom Ghebreyesus, has urged China to increase its transparency about the early days of the pandemic and allow greater access to its labs. Writing in the journal Science, Jon Cohen assesses the evidence for lab leak theories in this article, entitled ‘Call of the wild’.

Many lab leak theories rest on the proximity of the Wuhan Institute of Virology (WIV) to the initial outbreak. WIV, Cohen states, has long specialised in studying bat coronaviruses. Lab leak theorists argue that one or more lab workers could have become infected by an accident at WIV, then passed the virus to others. The lead bat coronavirus scientist at WIV, Shi Zhengli, denies this, and has stated that all staff and students in the lab were tested for SARS-CoV-2 and related coronaviruses, and all tested negative.

WHO reports from early 2020 also argued that early Covid-19 cases had links to multiple Wuhan animal markets. This evidence, some have argued, supports the idea of infected animals or animal traders bringing the virus to the city rather than laboratory scientists.

Others have argued that data from the start of the pandemic is “hopelessly impoverished”, and doesn’t support any firm conclusion on either side.

Cohen also covers the lab leak theories that argue SARS-CoV-2 is not naturally occurring at all, and was manufactured at WIV. Some argue that gain-of-function studies, where more virulent or more transmissible pathogens are created for scientific study, could have led to the creation of SARS-CoV-2. However, Cohen notes that the majority of scientists argue that SARS-CoV-2 can’t be a lab concoction, because no known virus is close enough to have served as its starting material.

Cohen concludes by acknowledging the large amount of unknown information around the origin of Covid, but also by quoting the evolutionary biologist at Harvard University, William Hanage, who says:

The space of possible stories in which there was a natural origin in or around the markets is much larger than the space of possible origins in which the Wuhan Institute of Virology is involved.

Read the full article: Jon Cohen, ‘Call of the wild’, Science, 2 September 2021

Variant variation

Katherine A Twohig, ‘Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study’, The Lancet Infectious Diseases, 27 August 2021

There are thousands of different variants of Covid-19 circulating across the world. The alpha (B.1.1.7) variant was first identified in England in November 2020 and spread quickly. The delta (B.1.617.2) variant was first identified in India in December 2020.

The delta variant now accounts for nearly all UK Covid-19 cases. In this major study for Lancet Infectious Diseases, researchers studied the severity of the delta variant compared with the alpha variant, and assessed whether associations with hospital attendance for each variant differed.

For the study entitled ‘Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study’, patients with laboratory-confirmed Covid-19 between 29 March and 23 May 2021 were categorised depending on whether they had the alpha or the delta variant. The patients were then linked with data on vaccination, hospital care and mortality, using their NHS number and other data sources. Hospital admission data was also sampled for 7 June 2021 and was divided into two outcomes: hospital admission only, and attendance to emergency care followed by hospital admission.

Overall, the study analysed 43,338 alpha and delta cases. Of these, 34,656 patients were infected with the alpha variant, and 8682 patients with the delta variant. A significant decrease of patients with the alpha variant occurred in the period studied.

The study found that patients with the delta variant had more than two times the risk of hospital admission compared with patients with the alpha variant. The authors state that these findings suggest “that outbreaks of the delta variant in unvaccinated populations might lead to a greater burden on health-care services than the alpha variant”.

Read the full article: Katherine A Twohig, ‘Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study’, The Lancet Infectious Diseases, 27 August 2021