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A health care worker prepares a dose of Sinovac’s Covid-19 vaccine at the Salvador Sanfuentes public school in Santiago, Chile. While doubts have been raised about inactivated vaccines like CoronaVac, immunity should be measured in terms of cellular immunity, not antibody count. Photo: AP
Opinion
Adrian Wu
Adrian Wu

Omicron: why doubts over effectiveness of ‘traditional’ inactivated vaccines are overblown

  • Expert opinion based on in vitro studies of neutralising antibody levels should be properly debated in academic circles, but by itself is not helpful for policymakers
  • Hong Kong, with its quite high vaccination rate of about 80 per cent for the first dose, should aim at ‘flattening the curve’ of an Omicron wave, rather than preventing it
We are now entering the third year of the Covid-19 pandemic, and it looks like a fifth wave of predominantly Omicron infections can no longer be avoided. Instead of placing the blame for the inevitable on wayward Cathay employees, lawmakers and ministers, our energy is better spent charting the best course of action going forward.
The enemy has changed its strategy, and so must we. Omicron is far more contagious than previous variants, has a shorter incubation period, results in a higher proportion of asymptomatic carriers, and evidence so far suggests it causes less severe disease.

Based on these characteristics and given our finite resources, Hong Kong is unlikely to prevent the explosion in cases seen elsewhere. Therefore, we should be making contingency plans based on the predicted number of patients requiring hospitalisation and intensive care, and the capacity of our health care system to accommodate them.

Our policies should aim to “flatten the curve” to avoid overloading our hospitals, and no longer try to catch every single case to prevent community spread.

Hong Kong’s rate of vaccination for first dose is approaching 80 per cent. Even though very few people here have natural immunity from previous infections, our high (-ish) rate of vaccine uptake should still significantly reduce the disease burden on our community.
Some experts have recently publicised their opinion that inactivated vaccines, such as those produced by Sinopharm and Sinovac, might not protect against Omicron. But this opinion is based on in vitro – not in vivo – studies of neutralising antibody levels, and it flies in the face of conventional immunologic wisdom.

The “traditional” (and by inference inferior) vaccines that we received as children are still protecting us from hepatitis B, measles and mumps, long after the antibodies have dropped below detectable levels.

And to measure protective immunity against these viral infections, we need to test for cellular immunity, not antibody levels. The opinion on inactivated vaccines is worthless in helping the government make informed decisions, and sows public doubt and fear. I have lost count of the number of patients expressing despair over having chosen the “wrong” vaccine.

Such discussion should be kept within academic circles where the subject can be properly debated.

To see how well inactivated vaccines work, we should be studying the populations that have received these vaccines. Look at Chile, where 90 per cent of the population has been vaccinated, almost entirely with Sinovac’s CoronaVac. The seven-day moving average of the number of daily new cases during the peak of the first wave was 6,971 on June 16, 2020. The corresponding figure for deaths was 252 on June 13, 2020. For the second wave, the peak for cases was 7,294 on June 8, 2021, and for death, 133 on July 8, 2021.

People wait to get tested for the coronavirus disease at a mobile test truck, in Valparaiso, Chile, on January 3. About 90 per cent of Chile’s population has been vaccinated, almost entirely with Sinovac’s CoronaVac. Photo: Reuters

Deaths were lower the second time presumably because of better understanding of the disease, natural immunity after the first round of infections and a partially vaccinated population. The seven-day moving average for new daily cases as of January 25 stands at 15, 462, which is 212 per cent of the peak during the second wave. The corresponding figure for deaths is 17, which is only 12.8 per cent of the peak during the second wave.

Since deaths can lag behind cases by several weeks, that number might rise in the next few weeks, but there is certainly no evidence the country is suffering the same scale of calamity as during previous waves.

Granted, the demographics of the Chilean population are different than Hong Kong’s, and more people there might have natural immunity after previous infections. They seem to be leading pretty normal lives during the Omicron onslaught, after achieving a high rate of vaccination.

If Hong Kong continues with ‘zero Covid’, it will become a shell of a city

If the number of cases in Hong Kong explodes, we should apply severe restrictions to the not-fully-vaccinated population, for their own protection and that of our health care system. We should also restrict activities that might result in superspreader events, such as large gatherings.

However, we should relax other restrictions that would add little value in flattening the curve, but would further hurt our economy. By that time, the number of infected travellers that slip through our stringent pre- and post-arrival testing dragnet will be a drop in the bucket.

It would no longer make sense to continue the strict quarantine requirements and flight bans. Let’s hope this wave will mark the beginning of the end of our nightmare.

Dr Adrian Wu is a specialist in immunology and allergy. He is currently in private practice at the Centre for Allergy and Asthma Care in Hong Kong

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