With the roll out of the COVID-19 vaccinations now underway in Hong Kong , it ’ s likely you ’ ve got some questions around the vaccine . Dr David Owens helps answer the most common ones

It is easy to get lost in debates around the percentage efficacy of the different vaccines for Covid-19 . Ultimately all vaccinations have their impact in one of two ways :

• Direct immunity : This deals with the question : If I am immunised , how less likely am I to die or become seriously ill from a disease ? This is about benefit to the individual .

• Indirect ( Herd ) immunity : This deals with the question : If lots of people in the population are vaccinated will people who have not been vaccinated also be protected ? This is a measure of benefit to the population .

Fortunately , all of the vaccines seem to be very good at reducing the risk of serious illness and death in vaccinated individuals . Here is some data from Israel which now has a very large data set .

Preventing SARS-COV-2 infection 91.9 % 95.8 %

Preventing disease with fever or respiratory symptoms

Preventing COVID-19 hospital admission

Preventing serious disease from COVID-19

96.9 % 98 %

95.8 % 98.9 %

96.4 % 99.2 %

Preventing COVID-19 death 94.6 % 98.9 %

Table 1 : Effectiveness of the Pfizer / BioNTech vaccine compared to unvaccinated population . Israel Health Ministry data to 13 Feb 2021 , data corrected for age .

We also have increasing evidence that the vaccines reduce milder cases and transmission to some degree . The issue of herd immunity is a little more complex

Are the COVID-19 vaccines safe ? Answer : YES

We now have data from many millions of vaccine doses and the side effect profile seems to be comparable to many other vaccines which are given routinely . Some mild side effects are relatively common . The RNA vaccines ( Pfizer-BioNTech in Hong Kong ) generally have slightly more mild side effects and a higher incidence of severe allergic reaction then the more traditional vaccines ( Sinovac ). It is estimated that severe allergic reaction occurs in between 4 – 11 cases per

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