On Thursday, 25 March, GLG, in partnership with the American Club, held an informal breakfast discussion with Professor Ivan Hung, co-convenor of the Expert Committee on Clinical Events Assessment Following Covid-19 Immunisation. During the breakfast, Professor Hung shared his candid perspective on the variety of vaccines supplied to Hong Kong.

Topics included:

• Overview of the vaccines supplied to Hong Kong
• Results of clinical trials and recommendations
• Distribution timeline, priorities, and logistical challenges

This article summarizes the Q&A session that followed Dr. Hung’s presentation. Click on this link to read the presentation summary.

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Can you give us some insights into how the Hong Kong government made its vaccine purchasing decisions?

From the start, the government tried to purchase vaccines from various platforms, based on the idea that if one platform failed, another would protect the public. Pfizer-BioNTech and Sinovac were the first to approach the government and were able to secure contracts because of their safety profiles and the efficacy data published in their phase one, phase two, and phase three trials. In Sinovac’s case, that phase three data came in slowly.

Now we’re looking at a third and possibly a fourth platform. The third, of course, is AstraZeneca, but we’re still waiting for results on its efficacy against variants. If that proves satisfactory, AstraZeneca will come on sometime in June or July.

Can you explain the differences among the vaccines?

The Moderna and Pfizer vaccines are basically from the same mRNA platform, while the Sinovac and BioNTech versions are inactivated vaccines. The Johnson & Johnson and AstraZeneca vaccines are Sputnik Vs.

In layman’s terms, what does it mean when you say that Moderna and Pfizer, for example, are from the same platform?

It means that they are based on the same RNA technology and that the way they are formulated is very similar. The reason we chose Pfizer instead of Moderna is probably because of Pfizer’s better supply chain.

Some of the data from the U.S. show that the Pfizer vaccine provides better immunity against variants than Moderna. Why is that the case if they are basically the same?

It’s probably due to some differences in the spike protein parts and RNA segments used by each. That may cause a difference in terms of immunogenicity against variants. Nevertheless, I think it’s still too early to say whether Pfizer actually outperformed Moderna on variants because we have little data.

Recently, there was an article that said vaccines may affect sperm count. What are the risks of the vaccines?

There’s no evidence that the vaccines cause reproductive problems, and there’s no need to worry about that because the vaccine can’t escape a cell once it enters it. The fact is, RNA molecules are very unstable and need a lipid nanoparticle wrapped around them until they reach their target. But once the molecule gains entrance into a cell, the nanoparticle quickly disintegrates. So there’s no reason to worry that it will affect other systems.

Given your work with your international colleagues, how do you think various governments will approach mutual recognition of vaccines?

Eventually, it probably will come down to a vaccine being recognized for efficacy by the World Health Organization. Countries would agree on which vaccines they accept, and there would be a form of vaccine visa that would permit international travel.

What would be your preferred vaccine for someone who is allergic or who has a chronic health issue?

The worry over allergies involves polyethylene glycol, which many people are allergic to and which is one of the contents in the BioNTech vaccine. We screen for polyethylene sensitivity before administering a vaccine. For those whose condition is very stable and who are already on medication, there’s no problem with getting vaccinated. But those with a symptomatic chronic illness and, for example, still have chest pain or shortness of breath when exercising,  we recommend getting your illness treated first.

What is your outlook on herd immunity in Hong Kong? What percentage of the population will need to get vaccinated before you feel we’re headed there?

Hong Kong is very different from the rest of the world. We have relatively few cases in the whole population. That actually causes a problem because it means we have to vaccinate about 70% of the adult and pediatric population in order to achieve herd immunity. I think children ultimately will get vaccinated because they can be carriers even if asymptomatic. Hopefully, we’ll be able to achieve that before the end of the year. But once you get to above 50%, you will see that cases drop dramatically. With multiple platforms being rolled out in China, half the population should be vaccinated before August.

The question that probably everyone wants the answer to is which vaccine is the most effective?

Each vaccine has its pros and cons.

BioNTech has robust efficacy against the variants and very good cell-mediated immunity. The downsides are that is has slightly high side effects and it contains polyethylene glycol, which is an allergen for some.

Sinovac, which is the inactivated vaccine, has very few side effects. It is very good at neutralizing antibody stimulation, but the cell-mediated immunity is slightly weak, which means it is probably less robust against the variants. Some may need a third dose by using a variant as the antigen. But I think the pharmacy group is doing research on that.

Novavax provides very, very good immunity and very good efficacy. It has a very safe profile.

AstraZeneca has very good immunogenicity, and you can have your second dose much later. And the question about thrombosis has been cleared up; the drug is not associated with a high risk of blot clots.

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About Professor Ivan Fan Ngai Hung

Professor Ivan Fan Ngai Hung is currently Ru Chien and Helen Lieh Endowed Professor in Health Sciences Pedagogy, Professor of Medicine and Assistant Dean (Admissions), Chief of the Division of Infectious Diseases, Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, and Honorary Consultant in Queen Mary Hospital, Hong Kong. He is also Clinical Professor and Chief-of-Service of the Department of Infectious Diseases and Clinical Microbiology at the HKU-Shenzhen Hospital.