Study results

Why was this study done? 

• COVID-19 can still infect some people even if they have been previously vaccinated or infected. Researchers wanted to better understand why some people become infected while others do not, and which parts of the immune system help protect against infection.   

• To answer this question, researchers used a controlled human infection model (CHIM). This type of study can uniquely address scientific questions around infection and immunity. The results from this study can help the development of new vaccines and treatments that will better protect against future variants and reduce spread. 

What happened in the study? 

• Healthy young adults aged 18-30 were given the Delta variant of the COVID-19 virus under close medical supervision and in controlled conditions. The virus was given as nasal drops.  

• The study started with a low dose of the virus. After review by an independent safety committee, the dose was gradually increased to improve the infection rate (the number of participants becoming infected with the virus) so the study questions could be answered. At the highest dose, participants were then selected for low COVID-19 antibodies because people with higher antibodies were still resisting infection.  

• Participants stayed in a quarantine room for up to two weeks after being given the virus where they were closely monitored and lots of samples and data were collected. They were followed up for a year.  

What did the study find? 

• Among the participants selected for lower starting levels of protective antibodies, one third (33%) developed mild to moderate Delta COVID-19 infection. 

• No participants developed serious side effects or serious illness (known as serious adverse events).  

• Participants with stronger antibody protection in their blood and in their nose before exposure were more likely to avoid infection completely. 

• Antibodies and T cells (another part of the immune system) were also linked to infections that were shorter and had fewer symptoms.  

What do the findings mean? 

• This controlled human infection study can safely answer key questions about how the immune system protects against COVID-19 infection.  

• The findings will help researchers develop and test next-generation vaccines and treatments that aim to block transmission or work across variants.  

Thank you to all the COVHIC002 participants who took part and to all the researchers who worked on this study.