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Vaccines for COVID-19


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?

Good news:

• 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.


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