A Guide to COVID Vaccination Immunity and Antibodies

We explore how the COVID vaccination program and exposure to the virus has affected immunity levels and how you can get a COVID antibody test.

Dr Claire Merrifield MBBS MRCGP PhD

March 2nd, 2022

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As we enter a stage of the coronavirus pandemic where a return to normal is coming closer and closer, the question of immunity is one many people are thinking about. Whether it’s in response to the COVID vaccine or infection, many of us are wondering how long we can expect to be protected from coronavirus. A COVID antibody test can provide insight into whether your body has developed antibodies against coronavirus and we’ll explore how you can get one in this article.

What are Coronavirus Antibodies?

Antibodies are molecules produced by the immune system to fight infections. When the body is infected with a new virus, the immune system produces antibodies against different parts of the virus. For coronavirus, there are several different types of antibodies.

One antibody detects a part of the virus called the “nucleocapsid” protein (N-antibody). If you’ve got this antibody present in your bloodstream it means that, at some point, you’ve been exposed to coronavirus (SARS-CoV-2) and your body has made defences against it.

Another type of antibody your body usually produces detects the coronavirus “spike” protien (S-antibody). Again, presence of this antibody in your blood can mean that you’ve been exposed to the virus. However, you can also have this antibody if you’ve just had a coronavirus vaccine as the vaccine tricks our body into producing an immune response against the spike protein. Often, these antibodies stay in the body for a long time and provide protection against future infection.

Antibody Response to Infection with Coronavirus

It takes around five to 14 days for your body to produce antibodies once exposed to coronavirus, and there’s ongoing research to see how long this antibody response lasts.

A study of 1,107 people in Iceland who recovered from coronavirus found that about 90% of people developed antibodies1. Four months later there was no decline in their antibody levels. Another study found that even people with mild cases of COVID-19 produced antibodies for around five to seven months2. Interestingly, they found that the N-antibodies tended to decline quicker than the S-antibodies.

This is important as it suggests that you’ve got some protection from coronavirus for several months after the initial infection. However, the answer to the question of ‘can you get COVID twice’ seems to be yes, in some cases. Re-infection with coronavirus does happen but current data suggests that a second infection tends to be less severe.

How Long do Coronavirus Antibodies Last Following COVID-19?

Antibodies stay in the bloodstream for different amounts of time. For some infections, such as chickenpox, those infected as a child will still have antibodies many years later. However, for infections like SARS-CoV-2 we think antibodies are likely to last for a much shorter time. For example, we know that antibodies against SARS, a closely related virus to SARS-CoV-2, generally last for around two to three years. Recent evidence suggest that antibodies against SARS-CoV-2 produced from infection could last up to 20 months3.

Doctor giving COVID vaccination in clinic

Antibody Response to Coronavirus Vaccination

Vaccines work by stimulating the body to create an immunological ‘memory’ of an infection without having the illness itself. Part of this defence is the production of antibodies to attach to the virus and alert the rest of the immune system to attack. All the major coronavirus vaccines (including AstraZeneca/Oxford and Pfizer/BioNTech used in the UK) work by creating a response against the virus spike protein. This means that after two doses of the vaccine, most people who are protected will have spike antibodies in their bloodstream.

How Long Will it Take to Build Immunity After Getting the COVID-19 Vaccine?

It’s estimated that it takes the body around one to two weeks to develop antibodies in response to the vaccine. This means that it’s possible to contract the virus still in that two week period, which is why proper hand hygiene and other precautionary measures are still recommended in that window.

Woman scheduling agenda

How is Immunity Against COVID-19 Achieved?

There are two main ways to achieve immunity against COVID-19 – either contract the virus or have a vaccination against it. Both of these scenarios give the same result – the body producing antibodies. The high numbers of COVID-19 cases in the UK throughout the pandemic meant that many people were developing antibodies through contact with the virus, resulting in a level of herd immunity. In addition to this, the government’s hugely successful vaccination program was also vital in protecting the millions of people who hadn’t contracted coronavirus.

Effectiveness of the COVID Vaccine

The vaccine has been proven to provide extensive protection against severe symptoms of COVID-19 in a number of different research projects.

Another way to see how effective a vaccine has been is by checking antibody levels in people who’ve been vaccinated. For example, with hepatitis B, we know that a blood level of over 100 IU/L is protective. In regards to COVID-19, it appears that the vaccine has indeed been extremely effective. The latest data from REACT-2 showed that nearly all of double-vaccinated adults developed antibodies after two weeks of having their second COVID vaccine4.

Data from the Office of National Statistics indicates that two doses of the Pfizer or AstraZeneca vaccine are estimated to provide 96% and 92% protection against hospitalisation with the Delta variant, which has played a huge role in helping the NHS stay afloat and save lives5.

Taking a COVID-19 Antibody Test

Antibody testing was widespread throughout the pandemic, but since the announcement by the government to move away from universal free testing, this includes antibody testing too. In order to qualify for a free COVID antibody test, you must be:

  • Taking part in a research study.
  • Taking part in a COVID-19 antibody test survey.
  • Offered an antibody test after a positive PCR test.

If you’re eligible to take a COVID antibody test, you’ll receive your coronavirus antibody test kit and can carry out the test at home. You’ll need to send off your finger prick blood sample and your results will tell you if you have detectable antibody levels against coronavirus.

What Does my coronavirus Antibody Test Result Mean?

N-antibody positive: You likely had infection with coronavirus at some point in the past.

S-antibody positive: You either had an infection with coronavirus at some point in the past or have had the vaccination.

N- and S-antibody positive: You were infected with coronavirus at some point in the past and you may also have been vaccinated.

S-antibody positive and N-antibody negative: Most likely you’ve been vaccinated against the virus but have not had previous infection.

References

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