By Siddharth Sridhar, clinical assistant professor from the Department of Microbiology, University of Hong Kong
Even in these difficult times, there is reason for hope.
I last posted on vaccines in early May and a lot has happened since then. The pace of vaccine design and trial evaluation has been rapid with nearly all frontline contenders posting preliminary results in humans. So, do they work?
• Most vaccine candidates appear to induce good antibody responses against SARS-CoV-2 in humans during the study periods.
• For some candidates, we also saw a good T-cell response, which is an important but under-studied arm of the immune system.
• Most vaccine candidates appeared to be safe during the study periods.
• Phase III trials are already ongoing in countries like Brazil and UAE to confirm that these vaccines really work.
• Multiple vaccine designs are being trialled (mRNA, DNA, inactivated virus, adenovirus vector vaccines) increasing the chance that one or more of them will eventually become a good vaccine.
• Big names like AstraZeneca and Pfizer are associated with these vaccines, guaranteeing production and distribution networks.
What are the challenges?
• The all-important phase III trials, which directly test whether these vaccines can protect humans against COVID-19. I expect to see initial reports of phase III by the end of this year. Many many vaccines against other infections have died in phase III, so this is a key litmus test.
• We need to map out the long-term efficacy and safety of each of these vaccines. The published studies only follow-up people for a few weeks. What happens a few months after vaccination? We don't know, but we will find out by 2021.
• Sorting out production/ distribution logistics, which is a daunting challenge. For example, we not only need billions of vaccine doses, but also millions of glass vials to contain these doses.
• How will wealth disparity between countries affect vaccine distribution? This is going to be one of the key issues once we actually have a good candidate. The key is to have more than one successful candidate, produce in low/middle income countries, and ensure reserved quotas for these vulnerable regions.
In the middle of a difficult pandemic where antivirals have largely proven disappointing, it is refreshing and inspiring to see the ingenuity and hard work going into these vaccine studies.
Stay hopeful. Have a good physically-distanced weekend.