Survey: How common are side effects of COVID-19 vaccines in Hong Kong?

Written by Dr David Owens

The most common concern expressed in populations with low vaccine uptake is safety. Sometimes this is voiced as a specific worry, such as the potential association of thrombosis post-vaccination. Often it is couched in general terms, for instance, the belief that the ‘vaccines have been rushed’.

Side effects of vaccination can be divided into those which happen shortly after the vaccination and resolve without any long term complications and those which either cause long term complications or occur later. Up to date, more than 2.75 billion doses of COVID-19 vaccines have been given worldwide. We now have a really good handle on the side effect data, especially for the BioNTech vaccine.

We recently surveyed 3,233 OT&P patients who had been vaccinated. Although the majority reported no or minimal side effects, a small but significant percentage of people reported more significant post-vaccine symptoms with 9.9% taking time off work.

Side effects were less common with Sinovac than the BioNTech vaccine. 79.5% of patients taking Sinovac reported no side effects compared to 50.4% taking BioNTech. 4.8% of patients who took Sinovac ranked their side effects as between 6-10 on a severity scale (moderate to severe) in comparison to 8.4% who took BioNTech.

From international studies, we have an increasing understanding of some very rare but serious potential side effects with some COVID-19 vaccines. The recent serious side effects potentially relating to the AstraZeneca and Johnson and Johnson vaccines is counterintuitively a good example of the safety data around vaccination. The rare condition in question typically affects around 5 people per million per year. It seems to affect around 10 per million after vaccination (mostly younger females). This compares to the risk of thrombosis with the contraceptive pill (200 per million) or COVID-19 (>1000 per million). It is of course appropriate that any side effects are fully evaluated and in this case it is likely that this class of vaccinations will be reserved for older patients.

Regardless, we are currently identifying complications which are occurring at a rate of 1/20th of that attributable to the oral contraceptive pill which is available as an over the counter medicine in Hong Kong. It is also important to realise that these vaccines are not given in Hong Kong and the AstraZeneca order was cancelled following the publication of this safety data.

In our vaccine survey, there were no serious complications and only 2 out of 3,233 people indicated that the side effects would stop them from taking a further dose. At least in our population, it does not seem that side effects are a significant barrier to vaccination. The side effects are consistent with data published internationally. There is no reason to believe that vaccines in Hong Kong are any less safe and effective than they have been shown to be in the rest of the world. One in every 10 people in the world has now been vaccinated against COVID-19. Whilst elimination has been a very good strategy for Hong Kong it can only ever be a temporary strategy. In another article we explain this in more detail. We have only two options, either we let the disease burn through, in which case it will cause significant harm to our population, or we get high vaccine coverage. We have increasing evidence of effectiveness and safety for Covid vaccines. In another article, we assess which is the best of the two vaccines available in Hong Kong.

The full survey results are available here.