I believe in the effectiveness and safety of COVID-19 vaccines; as supported by plenty of scientific and clinical evidence. On 28 January, I received the third booster and I felt good.

During the fifth outbreak of COVID-19 in Hong Kong, I am intrigued to go through some data, for example, according to the COVID-19 vaccine weekly surveillance reports prepared by the UK Health Security Agency, the latest report released on 27 January 22 described some interesting points related to 1) vaccine effectiveness against infection, 2) effectiveness against symptomatic disease, 3) effectiveness against hospitalization, and 4) effectiveness against mortality.

According to the table above, there was still insufficient data to conclude the effectiveness against infection; in other words, a person might or might not be infected after up to three injections of the vaccine. As far as symptomatic disease was concerned, it was quite confident that the third injection was effective against symptomatic disease caused by either the omicron (medium confidence) or delta (medium to high confidence) variant. In terms of the effectiveness against hospitalization, the protection against delta was more apparent with medium to high confidence. It is worth noting that for the omicron variant, the data could suggest that the vaccine was not effective against hospitalization, or, the infection caused by omicron variant did not require hospitalization as hinted by a report from the BBC. We should be patient to analyze the data available in the next couple of months.

The table above also demonstrated the effectiveness against mortality or death, which was a major medical concern. Although the effectiveness against mortality related to delta infection was identified; the effectiveness against omicron variant was not yet conclusive because of insufficient data.

The table above presented the rates of COVID-19 infection, hospitalization, and death in the vaccinated and unvaccinated. Let us focus on the rates of cases presenting to emergency care and death within 28 and 60 days; indeed, if we look at the forth and fifth columns (from the left), unvaccinated people were more likely to be hospitalized. Furthermore, when we look at the sixth to ninth columns, we could notice that the rates of death were higher in the unvaccinated, with some more prominent figures among the elderly.

Then, let us refer to another paper studying the rate of death from The Lancet published in 2020. The proportions of deaths in people at the age of <65 years out of all deaths were 0.6-2.8%, 95%, and 80% for COVID-19, influenza pandemic 1918, and influenza pandemic 2009, respectively; the smaller the proportion, the greater the impact on those older than 65. The findings showed that people above the age of 65 were more affected by COVID-19. Moreover, the fatality or death rates showed a steep increase among people over 80 years old, no matter they were in Asia or Europe.

To get a rough idea, the figure above revealed some previous data of seasonal flu in the United States. Overall, the death rates were smaller than 1%. With reference to the experience in South Africa (as shown in the table below), Abdullah et al (2021) reported the death rates of hospitalized patients infected by the omicron variant and the previous variants to be 4.5% and 21.3%, respectively; though other news report from the United Kingdom and the United States tended to be optimistic: some might describe omicron infection as a cold; while some even suggested that omicron variant might offer natural immunity! Referring to the recent outbreak in Hong Kong, the death rate of omicron variant infection was zero (until 28 January 2022). Nevertheless, I have to point out that the fragmentary findings described above are not directly comparable; and so far there is no concrete evidence confirming the omicron variant to be a cold. Scientists ought to analyze the overall death rates of omicron infection among the vaccinated and unvaccinated to make the conclusion (it is indeed challenging; as the infections by the omicron variant might be asymptomatic or they might not require hospitalization). Is the overall death rate comparable to that of seasonal flu, or is it not?

Based on the information above, with some unknown bit related to the omicron variant, I am still quite convinced to encourage my friends and family members to get vaccinated. We should build up the ‘herd immunity‘ by vaccination to protect our society, especially the elderly.