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Health and Fitness

Testing For Antibodies After Getting A COVID-19 Vaccine

The introduction of the Covid-19 antibody testing allows people who could not get a COVID 19 PCR test while unwell and those who had a negative test PCR test result because they tested early or late for the virus an opportunity to know whether they contracted the coronavirus or not.

Presently, the COVID-19 antibody testing also used to check if people who have recovered the COVID-19 vaccine have had an immune repose to produce antibodies. The new COVID-19 antibody gives both qualitative and quantitative result, which means it tells whether you have an antibody or not and the quantity of antibody produced if present.

This test is known as the COVID-19 vaccine antibody test. The answers to the frequently asked questions by patients below about the COVID-19 antibody test will inform you all you should know about this test.

When should I get a COVID-19 antibody test?

It takes about 24 – 28 days after contracting the coronavirus for the body to produce detectable levels of antibodies, so you have to wait for about 3 – 4 weeks from the onset of symptoms to get a COVID-19 antibody test.

How is it possible that I had COVID-19 and tested negative of COVID-19 antibody test?

Some people do not develop IgG antibodies following a COVID-19 infection. Producing antibodies depends on your viral load, that is, how much of the virus you had in your system, some psychological factors and the strength of your immune response.

How long do COVID-19 antibodies remain in the body?

A study in Spain found that about 14 – 15% of people with antibodies shed them within two months, while the antibody level in others reduced over 3 – 9 months. The King’s college also backed up this study.

Some studies also suggest that the T cell, which are important white blood cells involved in immune response, has a memory of the virus even after the body sheds IgG antibodies.

When should I get tested after vaccination?

Different studies have shown that the best time to get an antibodies test is 28 – 35 days after receiving the vaccine’s second dose. Antibody testing after the first dose is available, but the immune response rate is higher after the second vaccine. No evidence is available to show that antibodies are detectable after receiving the first dose of the vaccine.

Reports from AstraZeneca show that a single dose of the vaccine gives a four-fold increase in COVID-19 antibodies produced in response to the virus spike proteins in 95% of participants within a month.

There was a T cell response for all participants, with the cells getting to a peak by the 14th day and remaining the same for two months following injection. In 91% of the participants, a SARS-CoV-2 neutralising effect was present after the first dose and a 100% neutralising effect after the second dose.  The level of the neutralising effect was similar to those in COVID-19 patients.

What tests are available, and what does the result mean?

The Roche quantitative antibody test is available for COVID-19 antibody testing. The Roche antibody test tells whether you are positive or negative for the antibodies and tells the number of antibodies in your body if your result is positive. This information is useful if you want to check your antibody levels over time.

However, its limitation rests on the test’s multifaceted nature, as it depends on other factors aside from the level of IgG antibodies in the body.

What level of COVID-19 antibodies indicates a successful immunisation?

The T memory cells and neutralising antibody play a vital role in an immune response and protection after vaccination. It is difficult to measure immunity, especially for a new infection. Studies are ongoing to know what constitutes an effective natural immune response, so it is difficult to say what a good vaccine-induced immune response is.

Another challenge to know a successful immunisation is the lack of pre-aligned or standardised measurement. Every laboratory uses different immunoassays to measure every aspect of the immune response.

The diversity in the testing methods in different laboratories makes a definitive measurement unavailable to measure a protective immune response. Standardisation will become available over time to allow scientists to understand the SARS-COV-2 virus, develop more vaccines and medications for the virus.

The available test will only tell whether the COVID-19 antibody is present and the quantity present in the body.

Will the result tell if the antibodies are from a previous infection or vaccination?

No, it will not. The test does not differentiate between the antibodies from a past COVID-19 infection and an immune response to vaccination.

How is it possible that my result is negative over 28 days after my second dose of the vaccine?

Vaccines are not 100% effective, and it is possible not to have an immune response after taking the vaccine.

  • AstraZeneca vaccine

This vaccine is adenoviral vector-based, gotten from COVID spike proteins and modified into a harmless vaccine.

After vaccination, an immune response occurs where the B cells lock the spike protein, producing a reaction alongside the T cells that creates neutralising antibodies. The clinical trials showed that this vaccine has an average of 70% efficacy. It requires two doses, administered four weeks apart to first prime the immune system to enable it to fight off the virus.

  • Pfizer and Moderna vaccine

This vaccine uses the genetic component of mRNA to send information to the cells to make spike proteins. The cells destroy the genetic mRNA when it reads the protein sequence and builds a spike protein.

The T cells will recognise the spike protein as a foreign substance and alert other immune cells like the B cells. The helper T cells activate the B cells to produce antibodies for the spike protein.

The Pfizer-BioNTech vaccine requires two doses, administered 21 days apart. A trial of this vaccine shows over 90% efficacy.

The Moderna mRNA-1273 vaccine also requires two doses of 100µg 0.5ml each, administered 21 days apart. The interval between the two vaccine doses can be 41 days, depending on some factors. This vaccine is 90 – 95% effective.

What is the antibody behaviour after the first dose of each vaccine?

The UK government has decided to extend the second dose of the vaccination. Although this decision is controversial and there is no data to support this decision, it arose from the UK government trying to protect more at-risk persons within a short time.

The AstraZeneca and Pfizer vaccine trials did not compare the efficacy of one dose and different dose spacing.

AstraZeneca conducted a trial in Brazil and the UK which involved the participants receiving the doses that different spacing periods. This trial showed that the longer spacing between the two doses (2 – 3 months) gave a greater immune response but a small number of participants.

Findings from Public Health England showed that the AstraZeneca vaccine offers significant protection against hospitalisation from COVID-19 infection from 21 days after the first dose. This suggests that only the first dose may protect against severe COVID-19 infections.

MHRA also found that only the first dose offers considerable protection in the short term, but both doses offer higher protection.

A New England Journal of Medicine publication stated that the Pfizer-BioNTech vaccine’s efficacy between the first and second dose, administered 21 days apart, is 52.4%.

According to PHE Green Book, the short term protection from COVID-19 vaccination starts after ten days of receiving the first dose, and the data gathered between day 15 – 21 of the Phase three trial showed efficacy to be about 89%. However, Pfizer stated that no evidence to show how much protection remains after 21 days.

How long will immunity last?

No data is available to show how long the protection with last because the vaccines are still new. Although the number of antibodies may reduce over time, the immune system already contains memory B and T cells that may retain the coronavirus information for years and possibly decades.

A recent study suggested that the immunity may last for 3 – 6 months, but there is no evidence to support this.

You can contact us to get a COVID-19 test and vaccine.

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