- Aug 9, 2021
- 2 min read

COVID-19 Serology Simplified

If you've been vaccinated or previously infected with COVID-19, chances are your blood serology results will be different from someone who hasn't been.

Now and probably for some time in the future, many of us may need this test to be done to prove our immunity to the virus. MOH announced earlier that Singapore citizens, permanent residents and long-term pass holders who received their COVID-19 vaccination overseas can get their immunization records updated in the national registry here when they return.

Here’s a quick breakdown of what you need to know.

What is COVID-19 serology?

COVID-19 serology involves blood tests that look at antibodies - proteins your body produces to attack viruses or bacteria in the blood. These antibodies are produced as a response to an actual infection, or to vaccination.

SARS-CoV-2, like other viruses and bacteria, has specific structures which the antibodies are built to target - antigens. Two key antibodies that are tested currently are the ones that target the antigen Spike protein (S protein) and Nucleocapsid proteins (N protein)

Diagram: https://www.lubio.ch/applications/coronavirus-research/viral-proteins#group_2839

What does a positive or negative result mean?

A positive result means that you have either had a previous COVID-19 infection or that you’ve been vaccinated. In general, vaccinated individuals develop the antibodies to the S protein, which is what mRNA viruses have been designed to develop. An individual who has a natural infection would develop antibodies for both and hence the N protein is more specific for past infections.

Negative results can be tricky. Though testing negative for antibodies may mean you have not been previously infected or vaccinated against COVID-19, it may also be that your body has not developed sufficient detectable antibodies after an actual infection. In some cases, it may even be a false negative.

The body takes time to develop antibodies after an infection, and these antibody levels may also decline over time. Hence, the timing of when the test is done is also important in determining the results.

Which serology test is the right one for me?

The answer is not as straightforward as it seems! It would really depend on the reasons for doing the test, requirements from the country you are intending to travel to, your vaccination or previous infection status.

Apart from looking at the S and N protein antigens, the tests may also look at IgM and IgG. IgM are antibodies that are formed early on after the body responds to a natural infection, and this is later replaced by IgG which persists in the body for a longer period.

If you do require a serology test to be performed, our team will be happy to help and assist you with the appropriate test!

We currently provide Serological testing for Verification of Overseas COVID-19 Vaccinations at $60 nett (GST incl.)