Why test for antibodies after receiving a Covid-19 vaccination?
The aim of vaccination is that your body develops competent immune cells and produces antibodies, with which it can quickly recognise and fight a specific pathogen, such as the coronavirus, in the future – ideally, before the disease even breaks out.
According to current knowledge, IgG antibodies play an important role in Covid-19 vaccinations. These antibodies remain in our bodies for a long time. They also include neutralising antibodies , which prevent the virus from entering the human cell. Overall, the antibodies support the immune system in fighting and destroying the virus.
The immune system produces different IgG antibodies, each of which acts against very specific protein building blocks of the virus. The exact type of antibodies detected in the blood therefore gives an indication of whether the person has been successfully vaccinated with the vaccines approved so far (anti-S1 antibodies), or whether they have been infected with Covid-19 (anti-NP antibodies) – or both.
Furthermore, study results that a higher number of anti-S1 antibodies after vaccination is associated with a lower risk of a severe infection in the future.
Please note: The antibody test cannot provide a 100 per cent accurate statement on whether a vaccination was successful. Besides the antibodies, other cells of the immune system, such as memory cells, also play a role in immunity. Even a vaccination that is not completely effective seems to reduce the risk of severe Covid-19 infections.
Who should take the test?
The antibody test is useful for all people who are either fully vaccinated– that is, they have already received two vaccination doses against Covid-19 – or who suspect that they have already had Covid-19 in the past. In both cases, the test can tell you if there are corresponding antibodies in your blood.
If you currently have the symptoms of flu or a cold and want to be tested for acute infection, an antibody test is not suitable. Antibodies cannot always be detected at an early stage of the illness. If you want to find out whether you are infected, a PCR test is more useful. This test will provide more certainty as to whether you have been infected with the SARS-CoV-2 virus.
Please note: The IgG antibodies examined in the test are only formed gradually, both after vaccination and after infection. In order for the results to be accurate, you should therefore not carry out the test too early. As a rule of thumb, you should wait at least three weeks after receiving the second vaccination dosebefore carrying out the COVID-19 Vaccine Effectiveness Test.
How does the test work?
The cerascreen® COVID-19 Vaccine Effectiveness Test is a collection self-test kit for home use. You take a small blood sample from your fingertip – when and where you want. To do this, prick yourself with a lancet and collect a few drops of blood on a dry blood card. You then send the card with the sample back to us, at which point your blood is analysed in a specialised medical laboratory.
The laboratory uses the established ELISA measurement method to detect the S1 and NP antibodies in your blood that the body produces against the coronavirus.
Once the analysis is complete, you will receive a notification by email or via the My cerascreen® app. You can then download your personal results report with your test results.
How conclusive is the test?
The cerascreen® COVID-19 Vaccine Effectiveness Test uses scientifically established measurement processes to analyse Covid-19 antibody blood samples. Such analyses are used, for example, in scientific studies investigating the effectiveness of vaccines or population coverage.
What do the results tell me?
The results report tells you which concentrations of anti-S1 antibodies and anti-NP antibodies against SARS-CoV-2 were measured in your blood sample. You will also receive reference ranges, above which the concentrations are considered relevant.
Anti-S1 antibodies are formed against S1 spike proteins on the surface of the coronavirus. They can usually be detected after successful vaccination with mRNA or vector vaccines – but also after Covid-19 infection.
Anti-NP antibodies are formed against the nucleocapsid protein of SARS-CoV-2, the main structural protein from inside the virus. Considering the currently approved vaccines, these antibodies are measurable after a Covid-19 infection. The nucleocapsid protein is not part of the proteins that are produced in the body by the vaccines and against which antibodies are then formed.
Conclusions you can draw from your results report depend on whether the anti-S1 and anti-NP antibodies were detectable in your blood:
- Detection of S1 and NP: You have most likely already been infected with Covid-19.
- Only S1 antibodies are increased: You have probably successfully formed antibodies after vaccination.
- Only NP antibodies are increased: You have probably already had Covid-19; vaccination is recommended for full protection.
- Neither S1 nor NP antibodies are elevated: No antibodies were detected indicating vaccination or past infection. If you have received a vaccination, we recommend that you seek medical advice. It may be possible to achieve better protection against severe diseases by using a different vaccine.
What is the ELISA method?
ELISA stands for ‘Enzyme-Linked Immunosorbent Assay’. It is the standard scientific procedure that laboratories use to detect antibodies in blood. ELISA is used, for example, in allergy tests or in the diagnosis of infectious diseases, and is also the established laboratory method used for antibody tests against SARS-CoV-2.
The ELISA method works as follows: A special laboratory plate is coated with the virus (the antigen); then your sample is added. If there are antibodies in the sample, complexes of antibody and antigen form on the plate after some time.
The laboratory then adds a special enzyme that is also bound to an antibody. If there are antibody–antigen complexes on the plate, the new enzyme antibody structures attach themselves to these complexes. The larger complex that is created is called an ELISA sandwich.
When these so-called sandwiches are formed, a chemical substance added to the enzyme is transformed into a dye that can be seen on the plate. The intensity of this colour later indicates whether there are antibodies in the sample and, if so, at which concentration.
What are antibodies?
If pathogens, such as viruses, get into your body, your immune system works at full speed to fight them. Among other things, antibodies are produced in the process.
These antibodies are targeted to fight off very specific pathogens. Specific antibodies recognise a particular virus or bacterium, bind to the pathogen and allow the defence cells to attack it.
Once your immune system has produced the antibodies, they stay in your body for a long time. How long depends on the class of antibodies. IgG antibodies, for example, are active in fighting viruses for years in some cases. As long as they are in the body, they can render the same virus harmless when they encounter it again. If this is the case, you are practically immune to the pathogen – this is called immunisation.
What is an antibody titre?
When it comes to how long vaccinations or immunity last, people often talk about the antibody titre or vaccination titre. Nowadays, the term is often used synonymously with the concentration of certain antibodies in our blood. For example, if you have a lot of IgG antibodies against SARS-CoV-2 in your blood, you would call this a high antibody titre.
Strictly speaking, a titre is a specialised procedure used to determine how many antibodies there are against a certain pathogen in your blood. In the process, blood is diluted further and further. The virus is then added to the various dilution levels (1:2, 1:4, 1:8 and so on). The highest dilution level at which the blood can still fight the virus is the titre. Thus, 1:1024 is a high titre, indicating there are many antibodies in the blood; 1:80 would be a low titre.
However, such titre measurements are used more for longer-known, well-studied infections. They are used, for example, to check the status of tetanus vaccinations.
Antibodies against SARS-CoV-2 are currently detected mainly via the ELISA method. This method allows the concentration of the specific antibodies in the blood to be measured. Above a certain threshold value, a blood sample is considered proof of immunity against the coronavirus. The cerascreen® COVID-19 Vaccination Effectiveness Test also uses the ELISA method.
How long does immunity last?
Studies from Canada and the United States, for example, have been able to detect neutralising antibodies for up to eight months after a Covid-19 infection. But it is not yet clear how long the antibodies usually remain in the body after vaccination or illness. Researchers are investigating this further – along with the question of how long people are immune to SARS-CoV-2 after vaccination or illness.
People in Ireland are now being asked to have their booster dose, which is normally with the Pfizer/BioNTech vaccine or Moderna vaccine. Research needs to be carried out regarding the effectiveness of a booster jab, as this is still considered a recent development.
Scientists also suspect that even after immunity has expired, there is still a certain degree of protection – what we call basic immunisation. In such instances, the coronavirus would presumably only trigger mild symptoms, such as a cough, cold and sore throat after a certain time.
What does vaccine effectiveness mean?
The effectiveness of the vaccines is currently a hot topic in the media. According to the vaccination studies, for example, the BioNTech/Pfizer vaccine is said to be up to 95 per cent effective, while the AstraZeneca vaccine is only between 60 and 82 per cent effective, depending on the study.
But what does effectiveness (efficacy) actually mean in this case? Effectiveness describes how much lower the risk of getting sick was for vaccinated people in the vaccination studies. With an effectiveness of 60 per cent, 60 per cent fewer people among the vaccinated fell ill with Covid-19 than among the unvaccinated.
However, effectiveness says nothing about how vaccination affects the severity of disease progression.
Data from the vaccination studies and also, for example, from Israel, where many people have already been vaccinated, show that even with lower effectiveness, the vaccines reduce the risk of severe infections, hospitalisations and deaths enormously. Even if vaccinated people fall ill, the disease is usually much milder than without vaccination. In Israel, for example, of more than 500,000 people examined who have received the BioNTech vaccine, no one has died at a later stage from Covid-19.
What do SARS-CoV-2 and Covid-19 mean?
SARS-CoV-2 is the scientific name for the novel coronavirus. The abbreviation stands for ‘Severe Acute Respiratory Syndrome Coronavirus 2’.
Covid-19 stands for the disease that the virus causes. It is the abbreviation of Coronavirus Disease-2019, which refers to the first outbreak of the disease in China in December 2019.
People of all ages can get be infected with Covid-19. It is less common in children under 15 years of age, but the infection has also been present in infants.
Severe and potentially dangerous infections mainly affect older people and people with pre-existing conditions (e.g. cancer, cardiovascular disease, diabetes, lung disease, asthma) and may also affect smokers.
What are the symptoms of Covid-19?
Mild or moderate infections occur in about 80 per cent of those infected. Symptoms include a (mostly dry) cough, fever and sometimes a cold – and even mild pneumonia.
Some infected people also feel no symptoms at all, but they are still contagious; they have so-called silent infection.
Meanwhile, studies also indicate that the loss of sense of smell and taste can be a sign of the coronavirus.
In severe cases, people infected with Covid-19 can suffer from severe pneumonia with breathing difficulties and shortness of breath and even life-threatening lung and organ failure.
According to the World Health Organization, other symptoms that are less common but have also been reported are:
- Sore throat as well as headache and aching limbs
- Loss of appetite and weight
- Nausea, abdominal pain, vomiting and diarrhoea
- Skin rashes
Where can I get the latest information?
There are many ways you can stay informed about the progression of the pandemic online. To keep up to date with developments regarding Covid-19, visit www.gov.ie – a government site that provides information on coronavirus as well as support, the latest announcements, guidelines and restrictions in place – and more.
You can also find out more about testing and quarantine, financial support and details on vaccination for England, Scotland, Wales and Northern Ireland.
How can I reduce the risk of infection?
The World Health Organization (WHO) has issued some recommendations on what you can do on a daily basis to reduce the risk of contracting Covid-19 for yourself and others.
The recommended actions include:
- washing your hands thoroughly with soap or disinfecting them,
- always staying at least one metre away from others and avoiding crowds and
- always coughing and sneezing into the crook of your arm and throwing away used tissues immediately.
Further information and recommendations are provided by WHO in this collection of questions and answers on Covid-19. Collection of questions and answers about COVID-19.
For whom is the test not suitable?
The COVID-19 Vaccine Effectiveness Test is not suitable for or is only suitable to a limited extent for certain groups of people:
- People with infectious diseases such as hepatitis and HIV, are not allowed to take the COVID-19 Vaccine Effectiveness Test.
- People with haemophilia should not take the blood test.
- Pregnant and breastfeeding women should only take the COVID-19 Vaccine Effectiveness Test under medical supervision. The reference values and recommendations do not apply to them, so they should seek recommendations on the test result from their doctor.
- The COVID-19 Vaccine Effectiveness Test is not suitable for children under 18 years of age.
The test is not intended for diagnosing acute Covid-19 infection. If you experience flu symptoms, contact your doctor or the public health department by telephone. You can also clarify acute symptoms with a PCR test.