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Further information about antibody test results

  • A positive antibody test means that you have been exposed to the COVID-19 virus at some point in the past or have been vaccinated against COVID-19. It does not necessarily mean you are infected with the virus now, although if you have had a positive swab test recently, the positive antibody test probably relates to this infection.
  • Not everyone who has had COVID-19 or who has been vaccinated becomes positive on the antibody test. Being positive means having levels of antibodies above a certain amount, seen in people who were so seriously unwell with COVID-19 that they got admitted to hospital. This means your result could be negative on the antibody test but you may still have developed some antibodies. Levels of antibodies can change over time and can fall after having had the infection or being vaccinated, so you can have a positive test result and then a negative test result.
  • So being negative for antibodies does not mean someone has not had COVID-19 and it does not mean someone has not been vaccinated. This also means you may not test positive for antibodies after being vaccinated. Some people test negative for antibodies after vaccination because it takes time for the body to develop them. Alternatively, it could be that their body has not developed enough antibodies to meet the threshold at which the tests register a positive antibody response, but that their antibody levels have still risen. As individuals we all respond differently, and it is the impact of these differences that our survey is trying to understand.
  • Finally, antibodies are only part of the way that our bodies fight infection. There are other parts of the immune system, for example, cells called T-cells, that also fight infection but we are not measuring these because they require a lot more blood and very fast processing that isn’t possible in the survey. So those without a detectable antibody response may still be protected against getting COVID-19. This is also the case if you have previously tested positive for antibodies and now test negative – even if your antibody levels have dropped these other parts of the immune system may still be protecting you. One of the reasons we are doing the survey is to work this out.