COVID-19: Top science stories of the week, from single shot vaccine results to asymptomatic spread

Vaccine candidate protects monkeys from infection in single shot

Monkeys that received an experimental vaccine for COVID-19 produced an immune response after a single shot, according to a study published in Nature. Researchers at Jannsen Vaccines and Prevention in Leiden, the Netherlands, and from Beth Israel Deaconess Medical Center in Boston, Massachusetts, gave 32 rhesus macaques a single dose of one of seven different versions of the vaccine candidate and 20 of them a placebo dose.

The vaccine uses a common cold virus, called adenovirus serotype 26 (Ad26), to deliver the SARS-CoV-2 spike protein into host cells, where it stimulates an immune response against SARS-CoV-2, the virus that causes COVID-19.

Six weeks after vaccination, all animals were exposed to SARS-CoV-2. All 20 animals that received the placebo dose became infected. The most optimal vaccine prevented lung infection all six animals that received it, and prevented nasal infection in five out of six.

“A single-shot immunization has practical and logistical advantages over a two-shot regimen for global deployment and pandemic control, but a two-shot vaccine will likely be more immunogenic, and thus both regimens are being evaluated in clinical trials. We look forward to the results of the clinical trials that will determine the safety and immunogenicity, and ultimately the efficacy, of the Ad26.COV2.S vaccine in humans,” said Dan Barouch who led the team.

The vaccine is on track to begin Phase III trials in September, which will involve around 30,000 participants and test for efficacy and safety. From over 135 vaccine candidates in the pipeline, latest will be the seventh to enter into Phase III trials.

Immune reaction to some common colds might provide protection against COVID-19

A study, published in Science, has found that some immune cells capable of recognizing coronaviruses that cause the common cold might also respond to SARS-CoV-2, the virus responsible for COVID-19.

The team, based at La Jolla Institute for Immunology, California, analysed immune cells called memory T cells and found that they recognize particular parts of several SARS-CoV-2 proteins. They then identified similar sequences in coronaviruses responsible for the common cold and showed that these sequences could activate the T cells that also respond to SARS-CoV-2.

Previous studies have found that some people who have never been exposed to SARS-CoV-2 indeed have immune cells that recognize the virus and this latest study adds to the theory that immunity to common cold coronaviruses could contribute to the difference in COVID-19 severity. Further studies are needed.

Confirmation that asymptomatic people transmit COVID-19

A new study published in JAMA Internal Medicine confirms that those not showing symptoms of COVID-19 can still transmit the virus. Until now evidence that asymptomatic people can pass on the disease has been anecdotal but a team in South Korea have shown that people without symptoms carry just as much virus in their nose, throat and lungs as those with symptoms, and for almost as long.

The study analysed samples taken between March 6 and March 26 from 193 symptomatic and 110 asymptomatic people isolated at a community treatment centre in Cheonan, South Korea. Of the initially asymptomatic patients, 89 — roughly 30% of them — appeared healthy throughout, while 21 developed symptoms.

The results of the South Korean study are in line with comments made by Anthony Fauci, who’s leading the response to COVID-19 in the United States. “The good news about COVID-19 is that about 40 percent of the population have no symptoms when they get infected,” Fauci said. “But even though you are likely not going to get symptoms, you are propagating the outbreak, which means that you’re going to infect someone, who will infect someone, who then will have a serious consequence.”

The fact that SARS-CoV-2 is now known to spread through those not showing symptoms, adds to the difficulty of identifying and isolating infected people. Expanding testing to populations not showing symptoms could be an effective way of combating this and help to contain the pandemic.