• Vaccine trials that deliberately infect healthy volunteers with COVID-19 to speed up development come a step closer.
  • A new study to understand the role of genetics in COVID-19 symptom severity begins.
  • The level of herd immunity gained so far will not be enough to help in preventing a second wave.

Human challenge trials poised to go ahead

The World Health Organization (WHO) has released new guidance on controversial challenge trials in which healthy volunteers would be deliberately infected with COVID-19.

So-called challenge trials could speed up vaccine development and have been used with other diseases such as malaria, typhoid and flu in the past. The main ethical concern with these trials for COVID-19 is that there is no known treatment if anything goes wrong.

After animal trials, vaccines are typically tested for safety and efficacy by comparing infection rates of a large group of people who have been given a vaccine against a large group of those who haven’t. As many people are practising self-isolation and social distancing during the current pandemic, it could take a very long time to find a large enough group of people who have been exposed to the virus to see whether a vaccine candidate would be effective or not. By deliberately infecting people with COVID-19, challenge trials allow this process to be sped up by relying on a smaller number of volunteers in order to see the results.

The WHO lists eight criteria that would need to be met for the approach to be ethically justified, including restricting participation to healthy people aged 18-30 and fully informed consent.

Coronavirus: A graphic showing how using a human challenge trial can accelerate the process of developing a COVID-19 vaccine
How challenge trials could speed up a COVID vaccine
Image: Eyal, N., Lipsitch, M., & Smith, P. G. (31 March 2020). Human Challenge Studies to Accelerate Coronavirus Vaccine Licensure. The Journal of Infectious Diseases.

Researchers unpick genetics of COVID-19

Scientists in the UK have kick-started a research project that aims to understand whether a person’s genetics may influence their susceptibility to COVID-19.

By comparing the full set of genes - or genomes - of 20,000 people currently or previously in hospital intensive care, with 15,000 people with mild symptoms, the researchers hope to understand the role of genes in symptom severity.

The results of the study - which will be shared globally - could help inform decisions about how to protect the most vulnerable members of society, and could reveal new approaches to treating the disease. The results of the first 2,000 genomes are expected in the next few weeks.

Estimates indicate no significant level of herd immunity reached so far

A study modelling the burden of SARS-CoV-2 in France has estimated that only 4.4% of the population, or 2.8 million people, have been infected so far. While this estimate is much higher than the number of cases confirmed through testing, it is too low for herd immunity to have an effect in controlling the pandemic. Preliminary results of Spain’s nationwide antibody survey (in Spanish), which collected samples from 36,000 households, appear to confirm these estimates with only 5% of the country’s population having developed antibodies.

Herd immunity is the effect where if a large proportion of a population is immune to infection, the disease is less or unable to spread because transmission to uninfected individuals is blocked by those with immunity.

A graphic showing how herd immunity functions to prevent a disease spreading through a population.
A graphic representation of how herd immunity can prevent or slow the spread of disease through a population
Image: Tkarcher / CC BY-SA

Vaccine opponents gaining ground in online battlefield

A research group at George Washington University has for the first time mapped the virtual battleground between pro- and anti-vaccine movements on Facebook - with alarming results.

Although anti-vaccine pages are less followed than pro-vaccine pages, there are more of them, they are growing more quickly and becoming better connected to undecided pages. The study found that if the current trends continue, 10 years from now online discussion will be dominated by anti-vaccine views.


While the study did not consider sentiment towards a COVID-19 vaccine, at a time when the only permanent exit strategy for the pandemic is a vaccine, it will be more important than ever for the benefits of vaccination to be clearly communicated.

A network map showing the connections of Facebook pages that are neutral, pro- and anti-vaccination
The study's network map showing how anti-vaccination Facebook pages are more central, numerous and connected than pro-vaccine pages.
Image: Johnson, N.F., Velásquez, N., Restrepo, N.J. et al. The online competition between pro- and anti-vaccination views. Nature (2020)

The role of normal conversation in spreading COVID-19

A new study suggests that talking might play a role in spreading infectious diseases such as COVID-19, just like coughing or sneezing. Published this week in The Proceedings of the National Academy of Sciences, the study shows that talking can propel thousands of droplets that can remain suspended in the air for between eight and 14 minutes. Although undertaken in a controlled environment that might not be reflective of everyday conditions where rooms are better ventilated, the results strengthen the case for precautions such as wearing masks and maintaining physical distance in confined spaces.