Coronavirus antibodies: how long do Covid antibodies last?

 

What are antibody tests and why are they important? How do they help us know how long Covid-19 immunity lasts? Within the context of the pandemic, antibody tests can determine if people have already had Covid-19 or if they have been vaccinated. Importantly, they can tell us which people are immune – thereby helping us return to life without restrictions and social distancing. 

Antibodies are microscopic proteins that help your body fight dangerous infections like Covid-19. They are the tool the immune system uses to identify pathogens. They set our body’s defence cells onto the pathogens, which can then render them harmless. The presence of antibodies in your blood can indicate if you have already been infected with a specific pathogen – in this case, with SARS-CoV-2 (coronavirus).

Now that more than 60 per cent of people in the United Kingdom have been fully vaccinated against Covid-19, one of the next important questions of the pandemic looms over us: How long will the effect of the vaccines last? Some vaccine manufacturers are already recommending booster vaccinations to maintain protection for particularly vulnerable groups. In the United Kingdom, these booster vaccinations are also already being given to at-risk groups.

In this article, we answer the important questions about coronavirus antibodies and the bigger picture. How long do Covid antibodies last? What are antibody tests, and how can they help us develop herd immunity? We’ll also reveal the current findings of our Covid-19 Vaccine Effectiveness Test.

Antibodies: what are they?

Antibodies are proteins that the immune system uses to defend the body from pathogens. In medical terms, these are called immunoglobulins.^[6]

Did you know that an antigen is a substance on the surface of a pathogen? Antibodies react with these substances, or more exactly, they bind to them. When an antibody is bound to a pathogen, defence cells can recognise it as an invader and try to get rid of it.

What different kinds of antibodies are there?

There are different classes of antibodies that are responsible for fighting different types of pathogens. The most important types of antibodies are:^[6]

• IgA antibodies protect us from different types of pathogens. They are present in different mucous membranes, such as our gut, airways and eyes.
• IgE antibodies fight parasitic worms. They also are responsible for allergies.
• IgM antibodies are the first line of defence for our immune system. They are active in the early acute phase of an infection.
• IgG antibodies are the rearguard of our body’s immune system. They are first produced two to three weeks after an infection has passed. They remain in the body for a long time and establish immunity. These kinds of antibodies are often used in testing for food intolerances.

Curious about this topic? You can discover more about IgE and IgG antibodies in our article on the differences between food allergies and intolerances.

Coronavirus antibodies: which antibodies are active against Covid-19?

The antibody types IgA, IgM and IgG are usually active against viruses. Studies show this is also true for SARS-CoV-2.

When your body is infected with Covid-19, your body begins little by little to produce coronavirus antibodies. In the early stages of infection, there are few to none; then your body starts to produce IgA and IgM antibodies. At later stages – sometimes even during the infection itself – your body produces IgG antibodies. IgG antibodies are more specific; they target the virus specifically. They also stay in your blood much longer, which is why it is better to test for these in a Covid-19 antibody test.^[7]

Covid natural immunity vs Covid vaccine immunity: is there a difference?

When we talk about natural immunity within the context of Covid-19 this when your body has developed coronavirus antibodies naturally, following a Covid-19 infection. As you may have guessed, vaccine immunity, or vaccine-induced immunity, occurs when your body has been able to develop antibodies to Covid-19 following vaccination.

Experts have explained the differences in natural immunity and vaccine immunity when it comes to coronavirus antibodies. Findings from various studies have suggested that a key difference between Covid vaccine immunity and Covid natural immunity is your body’s ability to recognise new virus variants.^[13] Vaccine-generated immunity may mean that your body will be able to effectively recognise and fight off new variants when they enter our bodies. 

As you can imagine, there is also hybrid immunity, which is when you have antibodies from both infection and immunisation. 

How long does Covid immunity last?

If we look at other coronaviruses, IgG antibodies can sometimes be detected up to three years later. IgG antibodies for other virus families – such as measles – remain for a lifetime. At this point, it cannot be said exactly how long coronavirus antibodies last, as the long-term studies are still ongoing.

The SARS-CoV-2 virus is the first of its kind. There are several members of the coronavirus family, like the SARS-CoV-1, which causes SARS, MERS and the common cold. SARS-CoV-2 is very different from the others in the group, which is why our immune systems are not as equipped to fight it.^[8]

As they remain a long time, IgG antibodies are a reliable way of finding out whether you have had a certain disease or have developed immunity to a pathogen.^[7]

What are antibody tests?

There are various types of antibody test that test for coronavirus antibodies, including IgG tests carried out with the ELISA method or neutralisation tests. Some of these tests are available to take at your doctor’s – some, you can even take yourself within the comfort of your home.

Are antibody tests worth it?

What are antibody tests? Antibody tests are designed to track and research the progression of Covid-19 in our population. They are intended to estimate the percentage of a population that has either been infected with the virus or received a vaccine. This information is crucial in order to make decisions on how to react to the pandemic and protect the public.

Why are some researchers pinning their hopes on antibody tests? Many people are unaware that they have had the virus. Often, people infected with Covid-19 experience mild symptoms that appear to be cold symptoms, or they experience no symptoms whatsoever.^[1]

Antibody tests cannot be used to reliably establish if you are currently infected with Covid-19. This is because the immune system only produced antibodies towards the end stages of an infection, and such a test is not useful for detecting infection in its early stages. To diagnose an acute infection, you can use a PCR test.

Which coronavirus antibodies should we test for?

IgM and IgA antibodies remain in the blood for a few weeks after an illness. If the infection occurred a while ago, they may already have disappeared. These antibodies are also not designed specifically for the virus. The probability that a test confuses these with antibodies for a different virus is fairly high.

By contrast, IgG antibodies remain in the blood for far longer – perhaps even for years. IgG tests therefore provide us with more accurate results because they can distinguish better between different coronaviruses. Experts therefore consider IgG measurements the most diagnostically relevant – when they are taken no earlier than two weeks after the beginning of the illness.

In a Chinese study, IgG and IgM tests could not return positive more than ten days after the start of an illness, as antibodies cannot be accurately detected before then. After 35 days, IgM antibodies could often no longer be detected.^[9]

How accurate are antibody tests?

IgG tests can provide very accurate results. This, however, is only the case when they are performed long enough after the infection started. Normally the antibodies can be detected around two weeks after the infection.

There are two factors that describe the accuracy of such tests: specificity and sensitivity. Both are measured as percentages and indicate how high the probability is that a result is correct. 

Specificity tells us how accurate a negative result is, so if a person was healthy. A high specificity means there is a low risk of a false positive. Sensitivity indicates how accurate the test measures if a person is sick, so how reliable a positive result is. A high sensitivity means there is a low risk of a false negative.^[10]

What is the Covid-19 antibody test sensitivity?

The standard for IgG Covid-19 antibody tests is the well-established ELISA analysis. Many labs report a specificity for their ELISA Covid-19 tests of 98 to 99 per cent.

In other words, the risk of getting a positive result when you actually don’t have antibodies is only one to two per cent. The accuracy of the result depends on when the sample was taken. Some labs even report a specificity of 100 per cent if the sample was collected at least 20 days after infection.^[2]

How does ELISA work? The blood sample is combined with the virus on a special lab plate. Later, an antibody-binding enzyme is added. If the right antibodies are present in the blood sample, then an entity consisting of the virus, antibody and enzyme is created. A substance is then mixed in, with which the enzyme reacts by changing colour. The degree of colour change indicates the concentration of antibodies.

Scientists have another tool to analyse antibodies in order to check for test errors. If a blood sample tests positive for antibodies, the sample can be tested again in another lab. This is called a neutralisation test and is meant to ensure no mistake was made and it is an accurate result.^[7]

How long do Covid antibodies last with the vaccine?

The vaccine manufacturer BioNTech released a study that attests to the high safety and efficacy of its vaccine – even six months after the second dose. According to BioNTech, the effect peaks seven days after the second vaccination, but then decreases by about six percent every two months.^[14]

Meanwhile, the US pharmaceutical company Johnson & Johnson reported that a booster six months after the first dose of their vaccine results in a twelve times higher number of antibodies.^[15] Moderna also reported that there are fewer vaccine breakthroughs in people who have not been vaccinated for that long – the company compared data from vaccinated people who received their second Moderna dose eight and 13 months ago, respectively.^[16]

However, all manufacturers state that their vaccines significantly reduce the number of illnesses and severe infections, even months after vaccination.

Coronavirus antibodies after the vaccine: what have we seen?

Other studies confirm that antibody concentrations decrease over time after vaccination. In one study in a nursing home, for example, antibody levels dropped by 84 per cent six months after the patients were fully vaccinated.^[17] We don’t yet know in detail how this affects Covid vaccine immunity, but some researchers see a link between falling antibody levels and diminishing protection against the virus.^[18]

We have analysed the results of our Covid-19 Vaccine Effectiveness Test – and our data confirms what previous studies have found.

Covid antibody tests: what does our data tell us?

cerascreen looked at the results so far of 613 antibody tests carried out in Germany, Austria and Switzerland between March and September 2021. A total of 1,567 customers took the test during this period – 613 of whom also provided all the necessary information for our analysis (for example, gender, age, etc.). This way, we ensured that only robust data was included in the analysis.

For the tests, the blood of various patients was examined for coronavirus antibodies. For this analysis, our laboratory experts primarily looked at anti-S1 IgG antibodies that the body produces after a vaccination.

In addition, these test participants completed a questionnaire about when they received which vaccine against Covid-19. We then looked at how many days had gone between vaccination and the time the sample was taken. Participants were also asked about their age and gender.

The analysis from these blood tests confirms some of the more recent findings published by vaccine manufacturers and scientists – that the concentration of antibodies in our bodies decreases significantly over time and is generally lower in older people.

How does antibody concentration change over time?

For the main vaccines, cerascreen’s results show very clearly that the antibody concentration is usually highest around three weeks after the second vaccine dose. After that, the concentration seems to decrease – the more time that went by, the fewer antibodies the test persons had in their blood.

The highest antibody levels were found in clients who received the Moderna vaccine, followed by those who received the BioNTech vaccine. The fact that Moderna vaccines elicit the strongest antibody response has also been shown in recent scientific studies – for example, after observing around 2,500 health workers in Belgium and a comparative study from the United States.^{[19, 20]}

How does age affect antibody count?

The age of the people tested was also an important factor in cerascreen’s data. The older the customers were, the lower their antibody levels were. This was seen with all vaccines, especially AstraZeneca. Again, our data confirms the results of previous research – and provide further evidence that older people could benefit from booster vaccines.

The results for 18- to 34-year-olds fluctuate strongly because the number of participants in this age group was relatively small. The straight line for the Moderna vaccine is because the 14 clients in this age group all had values above 100 U/ml (above the maximum reading) and we set such results all to 100 for the purposes of this analysis.

Please note: Gender had no significant influence on the antibody concentration in our analysis. 

How can we determine whether a vaccination is still effective?

To put it simply, there are two approaches:

• Experts can look at the effectiveness of the vaccine in practice – that is, how many vaccinated people still contract Covid-19.
• Experts can check laboratory values of the vaccinated population, mostly at certain IgG antibodies that the immune system produces after vaccination in order to recognise and fight the coronavirus.

What is the future of Covid-19 vaccinations?

What happens when there are hardly any antibodies left in the body? Are other memory cells in our immune system enough to establish basic immunisation and prevent severe infections in the future? How often will we need booster vaccinations? Answers to these questions will come with further long-term studies.

Until then, you can check your own antibody levels to get an idea of your vaccination status, for example with a Covid-19 antibody test. Such antibody tests are also useful if you have not just been vaccinated but have recovered from a Covid-19 illness recently. 

In order to achieve herd immunity, around 60 to 70 per cent of the population needs to carry coronavirus antibodies, according to experts. How far along we are in this process needs to be checked with antibody tests.^[2]

Coronavirus antibodies & antibody tests – at a glance

Which antibodies are active against Covid-19?

When your body is infected with Covid-19, your body begins to produce coronavirus antibodies. In the early stages of infection, there are few to none; then your body starts to produce IgA and IgM antibodies. At later stages, your body produces IgG antibodies. IgG antibodies are more specific; they target the virus specifically.

What are antibody tests?

There are various types of antibody test that test for coronavirus antibodies, including IgG tests carried out with the ELISA method or neutralisation tests. Some of these tests are available to take at your doctor’s – some, you can even take yourself within the comfort of your home.

How long do Covid antibodies last with the vaccine?

The vaccine manufacturer BioNTech/Pfizer released a study that attests to the high safety and efficacy of its vaccine – even six months after the second dose. 

Meanwhile, the US pharmaceutical company Johnson & Johnson reported that a booster six months after the first dose of their vaccine results in a twelve times higher number of antibodies.

More and more studies are being published, in which we can see the efficacy of various vaccines over longer periods of time.

What is the future of Covid-19 vaccinations?

As the results of more and more studies are published, it remains to be seen how often we will need booster vaccines to protect us from Covid-19. What scientists have stated, is that in order to achieve herd immunity, around 60 to 70 per cent of the population needs to carry coronavirus antibodies, according to experts. How far along we are in this process needs to be checked with antibody tests.^[2]

Sources

^[1]      Robert-Koch-Institut, ‘Coronavirus SARS-CoV-2 - SARS-CoV-2 Steckbrief zur Coronavirus-Krankheit-2019 (COVID-19)’, available at https://www.rki.de/DE/Content/InfAZ/N/Neuartiges_Coronavirus/Steckbrief.html, accessed on 31 March 2020.

^[2]      N. W. SPIEGEL Katherine Rydlink, DER, ‘Corona-Antikörpertests: Zu früh, um wahr zu sein’, available at https://www.spiegel.de/wissenschaft/medizin/coronavirus-wie-antikoerpertests-dabei-helfen-die-pandemie-zu-verstehen-a-2258edcd-a304-4ee0-83cc-76a24f340c45, accessed on 17 April 2020.

^[3]      Robert-Koch-Institut, ‘Wie viele Menschen sind immun gegen das neue Coronavirus? Robert Koch-Institut startet bundesweite Antikörper-Studien’, 2020, available at https://www.rki.de/DE/Content/Service/Presse/Pressemitteilungen/2020/05_2020.html, accessed on 14 April, 2020.

^[4]      NDR, ‘Das Coronavirus-Update mit Christian Drosten, Folge 33: Herdenimmunität noch lange nicht in Sicht’, available at /nachrichten/info/33-Herdenimmunitaet-noch-lange-nicht-in-Sicht,podcastcoronavirus192.html, accessed on 23 April 2020.

^[5]      DER SPIEGEL,‘WHO bremst Hoffnung auf Herdenimmunität’, available at https://www.spiegel.de/wissenschaft/medizin/who-bremst-hoffnung-auf-herdenimmunitaet-a-1a330878-ad55-4b59-a8c0-8ff736bff0ca, accessed on 23 April 2020.

^[6]      Kaufmann S. H. E. ‘Antikörper und ihre Antigene’, in Medizinische Mikrobiologie und Infektiologie, Suerbaum S., Burchard G.-D., Kaufmann S. H. E., Schulz, T. F. Hrsg. Berlin, Heidelberg: Springer, 2016, pp. 49–61.

^[7]      NDR, ‘Das Coronavirus-Update mit Christian Drosten, Folge 31: Eine Wiederinfektion bleibt unwahrscheinlich’ available at /nachrichten/info/31-Eine-Wiederinfektion-bleibt-unwahrscheinlich,podcastcoronavirus186.html, accessed on 16 April 2020.

^[8]      Li X. et al. ‘Evolutionary history, potential intermediate animal host, and cross-species analyses of SARS-CoV-2’, Journal of Medical Virology, vol. 92, no. 6, pp. 602–611, 2020, doi: 10.1002/jmv.25731.

^[9]      Liu, W. et al., ‘Evaluation of Nucleocapsid and Spike Protein-based ELISAs for detecting antibodies against SARS-CoV-2’, medRxiv, p. 2020.03.16.20035014, March 2020, doi: 10.1101/2020.03.16.20035014.

^[10]      Bautsch, W. ‘Requirements and Assessment of Laboratory Tests’, Deutsches Aerzteblatt Online, June 2009, doi: 10.3238/arztebl.2009.0403.

^[11]      NDR, ‘Das Coronavirus-Update mit Christian Drosten, Folge 36: Die Rolle von Kindern ist nicht geklärt’, available at /nachrichten/info/36-Die-Rolle-von-Kindern-ist-nicht-geklaert,podcastcoronavirus200.html, accessed on 4 May 2020.

^[12]      NIH Director’s Blog How Immunity Generated from COVID-19 Vaccines Differs from an Infection’, available at https://directorsblog.nih.gov/2021/06/22/how-immunity-generated-from-covid-19-vaccines-differs-from-an-infection/, accessed on 27 September 2021.

^[13]      British Society for Immunology, COVID-19 immunity: Natural infection compared to vaccination’, available at https://www.immunology.org/coronavirus/connect-coronavirus-public-engagement-resources/covid-immunity-natural-infection-vaccine, accessed on 28 September 2021.

^[14]      Thomas S. J. et al. ‘Six Month Safety and Efficacy of the BNT162b2 mRNA COVID-19 Vaccine’, July 2021, doi: 10.1101/2021.07.28.21261159.

^[15]     ‘Johnson & Johnson Announces Real-World Evidence and Phase 3 Data Confirming Strong and Long-Lasting Protection of Single-Shot COVID-19 Vaccine in the U.S. | Johnson & Johnson’, Content Lab U.S., available at https://www.jnj.com/johnson-johnson-announces-real-world-evidence-and-phase-3-data-confirming-strong-and-long-lasting-protection-of-single-shot-covid-19-vaccine-in-the-u-s, accessed on 23 September 2021.

^[16]     ‘Moderna Highlights New Clinical Data on its COVID-19 Vaccine | Moderna, Inc.’, available at https://investors.modernatx.com/news-releases/news-release-details/moderna-highlights-new-clinical-data-its-covid-19-vaccine/, accessed on 23 September 2021.

^[17]      Canaday D. H. et al., ‘Significant reduction in humoral immunity among healthcare workers and nursing home residents 6 months after COVID-19 BNT162b2 mRNA vaccination’, August 2021, doi: 10.1101/2021.08.15.21262067.

^[18]      Khoury D. S. et al., ‘Neutralizing antibody levels are highly predictive of immune protection from symptomatic SARS-CoV-2 infection’, Nat. Med., vol. 27, no. 7, pp. 1205–1211, July 2021, doi: 10.1038/s41591-021-01377-8.

^[19]      Steensels, D., Pierlet, N., Penders, J., Mesotten, D., Heylen, L. ‘Comparison of SARS-CoV-2 Antibody Response Following Vaccination With BNT162b2 and mRNA-1273’, JAMA, August 2021, doi: 10.1001/jama.2021.15125.

^[20]      Self, W. H. ‘Comparative Effectiveness of Moderna, Pfizer-BioNTech, and Janssen (Johnson & Johnson) Vaccines in Preventing COVID-19 Hospitalizations Among Adults Without Immunocompromising Conditions — United States, March–August 2021’, MMWR Morb. Mortal. Wkly. Rep., vol. 70, 2021, doi: 10.15585/mmwr.mm7038e1.