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Testing for antibodies after a COVID-19 vaccine

Testing for antibodies after a COVID-19 vaccine

COVID-19 antibody testing has provided important information to those who have not been able to test for COVID-19 while unwell or tested with PCR too late or early. It has helped people confirm that the illness they experienced was indeed COVID-19. It also has limitations as some people do not develop IgG antibodies after having COVID-19.

Now, COVID-19 antibody testing is being used as a tool to check whether a COVID-19 vaccine has worked to trigger a sufficient immune response. A new test has become available that not only gives a positive or negative result but also provides a quantitative result, ie. it tells you how many antibodies you have. This test has been referred to as the COVID-19 “vaccine antibody test” in some circles.

Below we have created a patient advisory to answer the most common questions, bring together the most recent research and give you all of the information you need to make an informed choice about COVID-19 antibody testing. We hope it is of help.

Testing after contracting COVID-19

When should I test?

IgG antibodies are detectable from around 24 – 28 days post-infection.

I definitely had COVID-19 but I tested negative – how is this possible?

Not everyone who is infected with COVID-19 develops IgG antibodies. This depends on viral load (how much of the virus you were exposed to), the strength of your primary immune response and other physiological factors.

How long do antibodies stay in the system?

A study conducted in Spain of 70,000 people, found that around 14 – 15% of people shed all of their antibodies within 2 months and for others, antibody levels declined over 3 – 9 months. These findings were echoed by King’s College. Some research suggests that T cells (one of the important white blood cells of the immune system) also play an important part and T cell memory can continue after IgG antibodies are shed.

Testing after your COVID-19 vaccination

When should I test after vaccination?

To the best of our knowledge, the best time to test is 28 – 35 days after your second dose. Although you can test for antibodies after your first dose, we don’t know the degree to which a single dose provides a sufficient immune response. The UK government roll-out of the vaccine has delayed the second dose to 3 months after the first, so we understand that you might be keen to be tested between the two. Although we are happy to conduct the test for you, you should be aware that there is no clear evidence available about whether antibodies are detectable after the first dose and when.

According to reports published by AstraZeneca in the Lancet, a single dose of the vaccination resulted in a four-fold increase in antibodies to the SARS-CoV-2 virus spike protein in 95% of participants one month after injection. In all participants, a T-cell response was induced, peaking by day 14, and maintained two months after injection. Neutralising activity against SARS-CoV-2 was seen in 91% of participants one month after vaccination and in 100% of participants who received a second dose. The levels of neutralising antibodies seen in participants receiving either one or two doses were in a similar range to those seen in convalescent COVID-19 patients.

Therefore if you do decide to test after your first dose of the AstraZeneca vaccine, you should aim to test around one month after your vaccination.

We have very limited information on testing after the first dose of the Pfizer or Moderna vaccine.

What test do you use and what does the result mean?

We use the Roche quantitative antibody test for those seeking to check their post-vaccination immunity response. Neither Abbott nor the rapid cassette is advisable for this purpose.

The Roche quantitative antibody test is helpful because it not only provides a positive or negative result but also provides the number of antibodies present. This is helpful to those who also want to monitor their antibody levels over time.

The Roche test has shown 100% specificity and sensitivity after 28 days.

The limitation of testing is that the immune response to the vaccine is multifaceted and not only dependent on levels of IgG antibodies so testing for antibodies will give you a partial picture only.

Can you tell me what level of antibodies is considered a successful immunisation for each vaccine?

Both neutralizing antibodies and T memory cells play a significant role in immune response and protection post-vaccination.  Measuring immunity is a complex process especially when it comes to a new infection such as SARS-COV-2. Scientists are still working to learn what constitutes an effective natural immune response therefore at present it is difficult for scientists to state definitively what a good vaccine-induced immune response would look like and it is not yet known what level, or titre, is needed for protection.

Another significant challenge is the fact that there is no standardised or pre-aligned measurement process across the globe. Each laboratory uses several types of immunoassay to measure the single aspect of the immune response. As a result of this diversity in testing methodologies being carried out in various laboratories around the world, there is currently no definitive set values for a protective immune response. In time, standardisation of assays will occur, allowing the scientific community to build a greater understanding of the immune response to the SARS-CoV-2 virus and further development of vaccines and therapeutics for COVID-19.

In summary, our test will let you know if you have COVID-19 antibodies and also tell you how many, but we do not have data yet to inform you whether your level is considered a successful immune response to the vaccine dose.

Will you know whether the present antibodies are because of a previous infection or because of my vaccination?

No, we cannot differentiate between the antibodies caused by a past COVID-19 infection and those developed as a response to your vaccination. If you have had a previous COVID-19 infection, you should let your nurse know.

I’ve had my second dose over 28 days ago but I tested negative – how is this possible?

No vaccine is 100% effective and it is possible that you did not have an immunity response to the vaccine.

AstraZeneca Vaccine

The AstraZeneca vaccine is an adenoviral vector-based vaccination. Researchers have taken the genes for the covid spike proteins and modified them into a harmless virus to make the vaccination.

Once the vaccination is given, an immune response is created by the B cells locking onto the spike proteins, which then with the help of T cells will start to proliferate and pour out neutralising antibodies that target the spike protein.

Clinical trials have shown that this vaccination has an efficacy rate of an average of 70%, ranging from 62-90%. The Oxford-AstraZeneca vaccine requires two doses, given four weeks apart, to prime the immune system to fight off the coronavirus.

Pfizer and Moderna Vaccine

Pfizer-BioNTech and Moderna vaccine uses the genetic material of messenger RNA to deliver information to our cells to make spike proteins. The genetic mRNA is destroyed by the cells once the cell’s molecules have read its sequence and built a spike protein.

The T cells recognise the spike protein as a foreign agent and raise the alarm to other immune response cells such as the B cells. The B cells are then activated by helper T cells that will then produce antibodies that target the spike protein.

The Pfizer-BioNTech vaccine requires two injections, given 21 days apart.  Trials of the two mRNA vaccines report efficacies above 90%.

The Moderna mRNA-1273 vaccine is given at a schedule of two doses (100 µg, 0.5 ml each) 28 days apart. If necessary, the interval between the doses may be extended to 42 days. It has overall efficacy of 90-95%.

The current government strategy is to delay the second dose of the vaccine. What do we know about antibody behaviour after only one dose of the vaccination?

The decision by the UK to extend the second dose vaccination is controversial as there is very limited data supporting this decision. This decision is taken by the UK government to protect the greatest number of at-risk people overall in the shortest possible time.

In both Pfizer-BioNTech and AstraZeneca vaccine, the trials did not compare different dose spacing or compare one with two doses.

AstraZeneca has conducted a trial in the UK and Brazil that include participants receiving different spacing between doses. The finding showed that a longer gap (two to three months) led to a greater immune response, but the overall participant numbers were small.

According to Public Health England, the Oxford-AstraZeneca vaccine provides significant protection against hospitalisation at 21 days after the dose one until 2 weeks after the second dose. This evidence suggests that the first dose might provide protection against severe COVID-19 disease. MHRA has also stated that, although optimal efficacy was achieved through two doses, both vaccines “offer considerable protection after a single dose, at least in the short term.”

A paper published in the New England Journal of Medicine stated that the efficacy of the Pfizer-BioNTech vaccine was 52.4% between the first and second dose (spaced 21 days apart).

The PHE Green Book indicates that short term protection for this vaccination starts after 10 days from the first dose. Looking at the data from day 15 to 21 on the Phase III trial, they have calculated that the efficacy against Covid-19 symptoms to be at around 89%. However, Pfizer has that there is no evidence how much the protection lasts beyond 21 days.

How long will my immunity last?

Due to the newness of the vaccination, researchers do not yet know how long protection will last. There is a possibility that the number of antibodies might decline with time but the immune system also contains special cells called memory B cells and memory T cells that might retain information about the coronavirus for years or even decades. Recent research suggests immunity may last 3 – 6 months but this is yet to be confirmed and it is too early to say for certain.


AstraZeneca PLC. COVID-19 vaccine AZD1222 showed robust immune responses in all participants in Phase I/II trial. (https://www.astrazeneca.com/media-centre/press-releases/2020/covid-19-vaccine-azd1222-showed-robust-immune-responses-in-all-participants-in-phase-i-ii-trial.html). Accessed January 2021

AstraZeneca PLC. What does immunogenicity mean in the context of COVID-19 vaccines? (https://www.astrazeneca.com/what-science-can-do/topics/disease-understanding/what-does-immunogenicity-mean-in-the-context-of-covid-19-vaccines.html). Accessed January 2021

Mahase, E. and Lacobucci, C. 2021. Covid-19 vaccination: What’s the evidence for extending the dosing interval?. Article 372:n18

Corum, J. and Zimmer, C. 2021. How the Pfizer-BioNTech Vaccine Works. (https://www.nytimes.com/interactive/2020/health/pfizer-biontech-covid-19-vaccine.html ) Accessed January 2020.

Cohn, A. and Mbaeyi, S.2020. What Clinicians Need to Know About the Pfizer-BioNTech COVID-19 Vaccine. (https://www.cdc.gov/vaccines/covid-19/downloads/pfizer-biontech-vaccine-what-Clinicians-need-to-know.pdf ). Accessed Jan 2021

Covid 19 prevention network. The Science of COVID-19 Vaccines and Monoclonal Antibodies. (https://www.coronaviruspreventionnetwork.org/coronavirus-vaccine-and-antibody-science/ ). Accessed January 2021

Centers for disease control and prevention. 2021. Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States.  (https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html)

Macdonald, A. 2020. COVID-19 Antibody Testing: S vs. N Protein. (https://www.technologynetworks.com/diagnostics/blog/covid-19-antibody-testing-s-vs-n-protein-340327). Accessed on Jan 2021

Leave a Comment

  • Barry Hudson says:

    I had the astra veneca vacation on 26th January, and no antibodies on 3rd March, what does this mean and what if any thing do i do regards Barry

    • Alya Shakir says:

      hi Barry – what test did you have? Not all antibody testing is appropriate post-vaccine. If you have taken the correct test (quantitative antibody test) that we provide, then this may be that you fall within the 10 – 15% of people for whom the vaccine was not effective. Before we draw that conclusion however, we recommend making sure you’ve had the right test.

    • Pete says:

      Those posting about negative test results (maybe relating to the type of test used) can you include info if you had post vaccine side effects too? i.e. if you suffer the unpleasant inflammatory response – headaches, chills, joint aches etc for up to 48hrs, that is indicative of the T-cell production being kicked into action. With the quantitive antibody tests discussed in the article there should definitely be degrees of positive result with it’s reputed sensitivity. If negative post strong side effects, that leaves unanswered reasoning. I’m sure no side effects can still result positive but can any more posts please include so an overview can be formed please?

    • Carol Fitzmaurice says:

      I’ve had a antibody test 4 weeks after a Covid jab. Results are that I’ve not contracted Covid 19 but what conserns me is I’ve tested negative for Covid antibodies. Does this mean I’ve to be extra careful? X

    • Naseem Muhammad says:

      I had my second dose of the AstraZeneca vaccine a couple of weeks ago. I did my rapid test for covid-19 antibody and found both IgG or IgM negative. Does the routine rapid antibody test is the best tool to look for antibodies or there is a special rapid test for covid-19 vaccine antibodies ??

    • Gordon Cain says:

      My husband had his first phizor vaccination on 23rd January. He had a antibody test on 9th April and he has negative antibodies now.. Does this mean that he has no protection against the virus?

      • Alya Shakir says:

        Dear Mr Cain, it depends what antibody test he had. If he has the Roche quantitative antibody test and tests negative, then it is possible he is in the percentage for people for whom the vaccine has not been effective. However, we strongly recommend having the Roche test before making that conclusion as most other antibody tests will test negative for post-vaccination antibodies. Immunity is made up of multiple aspects, one of which is antibodies.

  • Gayle Michelon says:

    I have read your article. Because I have Myeloma and in light of recent, if inadequate, research I would like to have an antibody test after my second dose of the Pfizer vaccine in April. Could you give an idea of when would be the best time ( ie how long after?) and where I could get this done. I live in Chesterfield, Derbyshire. Perhaps also there is a trial I could participate in to aid knowledge about this issue?

    • Alya Shakir says:

      hi Gayle! Based on the research provided by Pfizer and AstraZeneca, 28 days after your dose would be ideal. We aren’t running a trial here due to relatively small patient numbers and only have a branch in Central London. if you test elsewhere, please make sure they provide an antibody test suitable post-vaccine as some antibody tests are not suitable for this purpose.

      • Ali C says:

        Hi Alya
        I’m a kidney transplant patient in central London – how far in advance would I need to book to get an antibody test after my second dose of the vaccine? I’m keen to see if there’s any sign of the antibodies, the preliminary results for Pfizer in tx patients in the US don’t look positive!

        • Alya Shakir says:

          Hi Ali, thanks for your comment. You can book with us for a same-day or next-day appointment. Ideally, you should book from 28 days after your vaccine dose. Hopefully, the results will be positive for you!

  • Alan Keeley says:

    How do I get a test to ensure that my 1st vaccine injection was indeed given sucessfully

    • Alya Shakir says:

      hi Alan! You can book in for a quantitative antibody test with us. You’ll have the result in 24 hours.

  • Jane Helm says:

    I have had 1 astra zeneca covid vaccine , I tested negative for antibodies 1 month after what does that mean?

    • James hill says:

      Seems like this is a common theme. I had vaccine same time as a relitivr who had Pfizer, both tested week 3 – they had lots of antibodies, I have none .

      • Alya Shakir says:

        hi James – what test did you have? The instant tests and Abbott test aren’t suitable for detection post-vaccine.

    • Alya Shakir says:

      Hi Jane – what antibody test did you have? There is only one test that would detect these (the quantitative test we offer). The antibody tests used for post-infection such as Abbott or instant / rapid tests aren’t suitable. Please retest with the quantitative antibody test in the first instance.

  • Lisa Barnes says:

    If you have had both vaccines and the antibody results are negative, what are you expected to do? Thank You

    • Alya Shakir says:

      hi Lisa! What antibody test did you have? If you had an antibody test that only gives a positive or negative result, these aren’t appropriate for testing post-vaccination. This is why we recommend the quantitative antibody test we provide. We have had patients who tested negative on tests more suitable post-infection then show antibodies on our test. Please do book in if you’d like to check for antibodies. If that test is then negative, it is possible you are in the 10-15% of people for whom the vaccine is not effective. Hopefully that is not the case. We hope this is helpful.

  • Paula Matson says:

    I had my 2nd Pfizer vaccine 26th Feb and would like an antibody check. Where can I have this done please? I live in Bucks so can travel into London

    • Alya Shakir says:

      Hi Paula, you can have this test with us. Go to our online booking and choose A4: COVID-19 quantitative antibody test. We look forward to welcoming you.

  • Ali C says:

    Good article – if I’m trying to use the online booking tool to get the Roche test for antibodies after my second dose of the Pfizer vaccine, which test should I be booking from your list? It’s not clear from the list. Thanks!

    • Alya Shakir says:

      Hi Ali, please choose “A4 – COVID-19 quantitative antibody test”. Thank you for your feedback.

  • Linda Wright says:

    I had Covid antibodies prior to having vaccine. After 7 days I’m having long covid again. My joints hurt, I feel generally unwell. Should I have second dose of vaccine

  • Linda W says:

    I’m part of a Covid study at Oxford University and have had a blood and swab test every month since October. I had my first Pfizer vaccine on 2nd February but no booster yet. My blood and swab test on 02/03/21 showed I was negative for Covid but positive for antibodies. I had another blood and swab test on 27/03/21 but haven’t received the results yet. However today I had some NHS text messages and emails saying I was positive for Covid and I should start isolating immediately. I don’t understand what is happening since I have no symptoms, also shouldn’t I have had my Pfizer second jab by now? Thank you for any advice, from Linda

  • Jackie Smith says:

    I’m on the Uk Biobank programme. I had my first Pfizer vaccination on the 25th January 21 which caused a massive bruise.I had my second vaccination on the 31st March. I also carried out an antibodies test for Uk Biobank on the 31st March which proved negative I’m now concerned.

  • Lara Hobbs says:

    I had my first Pfeizer jab in Dec 2020 followed up with the 2nd one Jan5th 2021. I had a sore arm with the second jab, but nothing more. I tested negative for antibodies at the beginning of March. My GP told me it may be because the government antibody test is testing for C19 antibodies, NOT vaccine antibodies. Can you please enlighten me and direct me to a test, if necessary, relevant to the vaccine?

  • Tracey Stroud says:

    I am Autoimmune Rheumatoid Arthritis patient and Immunesurpressed I have had one Pfizer jab and had to wait 12 weeks in England for second there are rumours the vacvine has not worked for us would a antibody test after the second jab be helpfull as I have shielded for over a year so I definately have not had it

  • Tracey Tracey Stroud says:

    I live in Cheshire so I can not get to London can I please ask you if an antibody test called VirTus Quantative is the same as yours

  • Al says:

    What number of antibodies/mL should I be looking for in the lab result?

    • Alya Shakir says:

      There is no research defining the number of antibodies that would be considered a successful immune response. The quantitative test registers antibody levels in a range of 0.8 – <2000.

  • Martyn Barker says:

    I have had 2 blood tests since my Pfizer vaccine, but the results both said negative for antibodies. I am due my second vaccination about 23/24 April. I am keen to get another blood test after this. Can you do this please?

    • Alya Shakir says:

      Hi Martyn, do you know what test you had? We recommend the Roche quantitative antibody test. Patients have tested negative with other antibody tests and they do not use the same detection method needed for antibodies generated post-vaccine. You can call us on 020 7323 1023 to book.

  • Sameh Tawfik says:

    Post Astra COVID19 vaccine ,
    When to test ?
    Is it IgG ? / total ?
    Why second dose 3 months & not 1 month as previously ?

    • Alya Shakir says:

      Dear Sameh, you can test 28 days after your first and second dose. The test we provide is a Roche quantitative antibody test. It does look for total IgG and gives a quantitative result. You can book this on 020 7323 1023. We are afraid we do not know why the next dose timing has been changed by the government – recent evidence suggests this approach could still provide protection.

  • Eman Al Anani says:

    My husband had the Sinopharm vaccine (2nd dose on January 31st). He got tested a few days ago and his igG was 17.3. Is that an adequate number of antibodies?

    • Alya Shakir says:

      Dear Eman, unfortunately there has been no guidance from the vaccine manufacturers or government regarding expected antibody levels post-vaccine, therefore we cannot in good faith give an answer based in evidence.

Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine
Testing for antibodies after a COVID-19 vaccine

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