SARS-CoV-2 July update – part 2

Mutations allow virus to elude antibodies

Mutations in SARS-CoV-2 might help the virus to thwart potent immune molecules. The blood of many people who recover from COVID-19 contains immune-system molecules called neutralizing antibodies that disable particles of the new coronavirus. Most such antibodies recognize the new coronavirus’s spike protein, which the virus uses to infect cells. Researchers hope that these molecules can be used as therapies, and can be elicited by vaccines. Theodora Hatziioannou and Paul Bieniasz at the Rockefeller University in New York City and their colleagues engineered a version of the vesicular stomatitis virus, which infects livestock, to make the spike protein. They then grew the virus in the presence of neutralizing antibodies (Y. Weisblum et al. Preprint at bioRxiv; 2020). The spike protein in the engineered viruses acquired mutations that allowed the viruses to escape recognition by a range of neutralizing antibodies.

The team also found these mutations in SARS-CoV-2 samples from infected people around the world, although at very low frequencies. Treatment ‘cocktails’ of multiple neutralizing antibodies, each recognizing a different part of the spike protein, could stop the virus from evolving resistance to these molecules, the authors suggest. The findings have not yet been peer reviewed.

The power of China’s virus-control campaign is seen in pattern of symptoms

In China, a key metric of epidemics called the serial interval shrank drastically soon after the new coronavirus’s arrival — a finding that underscores the success of China’s testing and isolation efforts. The serial interval is the average time between the onset of symptoms in a chain of people infected by a pathogen. Benjamin Cowling at the University of Hong Kong and his colleagues modelled the spread of SARS-CoV-2 in China and found that the serial interval plummeted from 7.8 days to 2.6 days over a 5-week period starting on 9 January (S. T. Ali et al. Science; 2020).

The researchers say that early isolation of cases prevented transmission that would otherwise have occurred later in an infectious period, leading to fewer cases and slowing the spread of the virus. As a result, most of the remaining transmissions occurred either before infected people showed symptoms or early in the symptomatic phase, and the serial interval shrank. The authors suggest the serial interval distribution be used in real time to track the changing
transmissibility of the virus.

Severely ill people yield diverse trove of powerful antibodies

Scientists have identified a diverse group of antibodies that block the new coronavirus’s ability to infect cells, even when applied in low doses.The immune-system proteins called neutralizing antibodies interfere with hostile microbes trying to enter target cells. David Ho at Columbia University Vagelos College of Physicians and Surgeons in New York City and his colleagues studied neutralizing antibodies from the plasma of five people with severe cases of COVID-19 (L. Liu et al. Nature; 2020).

Nineteen antibodies proved highly effective at preventing SARS-CoV-2 infection of cell samples. A small dose of one of the antibodies protected golden Syrian hamsters (Mesocricetus auratus) from SARS-CoV-2 infection.

The 19 antibodies attach to a variety of locations on the coronavirus spike protein. A therapy made from antibodies
that fasten onto the spike protein at multiple sites could be difficult for the virus to evade through mutation.

Antiviral antibodies peter out within weeks after infection

Key antibodies that neutralize the effects of the new coronavirus fall to low levels within months of SARS-CoV-2 infection, according to the most comprehensive study yet. Neutralizing antibodies can block a pathogen from infecting cells. But such antibody responses against coronaviruses often wane after just a few weeks.

Katie Doores at King’s College London and her colleagues monitored the concentration of Coronavirus research updates: neutralizing antibodies against SARS-CoV-2 in 65 infected people for up to 94 days ( J. Seow et al. Preprint at medRxiv; 2020). In a preprint that has not yet been peer reviewed, the team reports that at the peak of antibody production, people with severe COVID-19 symptoms had higher levels of antibodies than had people with mild disease.

However, in most people, antibody levels began to fall about a month after symptoms appeared, sometimes to
nearly undetectable levels — raising questions about the durability of vaccines designed to promote the production of neutralizing antibodies.