The participants from this study were all from Wuhan, China, which is a limitation because geographic location can affect anti-ad5 immunity. For example, the proportions of neutralizing antibody titres for Ad5 of more than 1:200 appear to vary by country:

• India: 80%
• Kenya: 78%
• Thailand 67%
• South Africa: 60%
• Sierra Leone: 45%
• USA: < 30%

This is important because the researchers expect the vaccine to be more effective in those with lower anti-ad5-immunity and the vaccine to be less effective in individuals with higher anti-ad5 immunity.