Normally when giving vaccinations we assume the vaccine to be effective. There are some situations in which we test the presence of immunity. For example, we test people who are considering pregnancy or who are newly pregnant to ensure they are immune to rubella or chickenpox and we test healthcare workers and at-risk individuals to make sure they are immune to Hepatitis B post-vaccination. We do not routinely test individuals after Covid vaccinations as we do not yet have a specific threshold above which we know that protection occurs. We do know from studies both in Hong Kong and internationally that antibody levels wane after vaccination. We also know the BioNTech is a more effective vaccination than Sinovac.
Antibody Testing post-vaccination
There are a number of blood tests which measure antibodies against the SARS-Cov-2 virus. An IGG test becomes positive within the first few weeks of the illness or vaccination. We have an increasingly large dataset around the effectiveness of vaccination and the results are very impressive. At OT&P we consistently see high antibody levels after vaccination. This is especially so for BioNTech vaccination. Over 90% of OT&P patients were vaccinated by May 2021 with 96% of our patients choosing BioNTech. We reviewed the first cohort of antibody results which showed a mean antibody level of 8675 AU/mL and a median of 7580 AU/mL with a value of >50 indicating immunity. These results are compatible with the data reported out of HKU.
Example of post-vaccine immunity. Over 50 is considered immune. Most cases we see are measured in the thousands and it is not uncommon to see cases, as above, beyond the upper measurable limit.
How long will protection last for?
It is generally considered that the first series of vaccinations gives protection for six months. We now have very good evidence for the effectiveness of booster doses which not only boost the initial response but also increase levels beyond the first two doses. We also have increasing evidence of strong secondary immunity provided by T-cells and memory cells.