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COVID-19Immune System

COVID-19 - is anyone immune?

COVID-19 - is anyone immune?

December 4, 2020

COVID-19 - is anyone immune?

COVID-19 – is anyone immune?

We’re into our first ‘COVID winter’ and experts are still discovering what immunity to the virus means, and how long it could last. So, what do we know so far? We’ve spoken to Professor Adrian Hayday, Professor of Immunology at King’s College London, and our very own Dr. Kush Joshi to get the answers.

COVID-19 vaccinations are underway in the UK, with the first doses being administered to care home residents. The results of trials, from the likes of Pfizer and Moderna, were very encouraging, with some leading to 95% fewer cases of infection vs. the placebo group.

However, we’re still in the early stages of battling COVID. What we still can’t answer is how long vaccines will provide protection for and whether you’re protected if you’ve had COVID-19 already.

On top of that, even though vaccination programmes have started, they’re being offered to the most vulnerable people first. This means the rest of the country will have to continue observing recommended social distancing and COVID-safe hygiene practices to continue to protect ourselves from the virus.

What about natural immunity?

Historically, until a vaccine is developed the only way to have natural immunity to a virus is to have had it before. If someone has been infected, it is likely that they will develop antibodies – proteins made by the body to fight off the virus. The body then remembers how to make these if it encounters the same infection again.

“However”, says Dr Kush Joshi, UK medical lead for Melio Health, “because COVID-19 is a relatively new virus, researchers still do not know for sure if everyone who has had it will develop immunity, how long that immunity will last, or if it will protect against reinfection.”

What we do know is that studies[i] have detected antibody responses in most people who have had COVID-19 between 10-14 days after they became infected, with higher levels in those who had more severe disease.

But some research has also shown[ii] that these antibodies wane over time, with some reports[iii] finding they disappear faster in people who were infected asymptomatically.

The amount of antibodies you have, and how long they last in your blood, don’t tell the whole story though. As Professor Hayday explains:

“The biggest question is when you get 're-challenged', how quickly you can reactivate what we call ‘memory responses’. These are B cells that sit in your blood and bone marrow and if you can switch them on, like a light switch, then you don't have to worry about having a lot of antibodies because your body will make a lot of antibodies very quickly.”

This means, even if the antibodies in your blood fade over time, as long as your body’s B cells remain in a state to respond if you are reinfected, you will be able to fight the infection.

Reinfection risks

The chance that someone could get COVID-19 for a second time has been a concern for immunologists. These concerns have been fuelled by reports of a person in Hong Kong getting the virus for a second time, 142 days after catching it the first time. He was found to be virus positive after re-entry screening following travel abroad. Tests showed[ii] the first and second infections were different strains of the virus, with one possible explanation for the reinfection being that the person was not robustly immune following the first infection.

However, Professor Hayday believes these kinds of cases to be rare and widespread reinfection in a short time frame is unlikely.

T-cell protection

Antibodies aren’t the only line of immune defence we have to rely on. We also have T-cells.

Whereas antibodies help prevent cells from being infected, T-cells respond to infected cells[iv]. T-cells help tackle infections by coordinating other immune responses – such as boosting antibodies and enabling immunological memory – as well as killing cells that contain the virus[v].

Researchers at the University of Birmingham showed[vi] that a T-cell response to COVID-19 may last for at least six months after even after mild or asymptomatic infection, although they stressed that this does not mean that people cannot be re-infected.

Different levels of infection

Another unknown is how immunity will vary depending on how severe your infection was. COVID-19 can cause a range of symptoms – from the extreme where patients need to be hospitalised and can even die, to no symptoms at all (asymptomatic). The severity of your case could impact your ability to fight the virus off in the future. “If you have to get really ill to get really strong immunity that's not the situation we want to be in,” says Professor Hayday.

What can we learn from other diseases?

When trying to work out what will probably happen, Immunologists will look to related or similar diseases they’ve seen. But here there is “conflicting data”.

“It’s argued for seasonal coronaviruses, immunity is rather short lived and memory B cells are not very effective” Professors Hayday says, “By contrast, the data that exists for SARS infection back in 2002, I think looks moderately encouraging; 11 to 12 years after infection, researchers report seeing perfectly good T-cell responses and some evidence of B cell activity.”

What’s next?

Pfizer’s vaccine is already being administered to people in the UK, but there are still more vaccines to come. Vaccines from Moderna and AstraZeneca/Oxford University are currently in the approvals process by the Medical and Healthcare products Regulatory Agency (MHRA), with hopes that the Oxford vaccine could be approved by Christmas. Other companies, like GSK, are working on other types of vaccines which could give us more ways to fight the disease.

“When the 'heavy players' come in like the GSK protein vaccine, which is fundamentally a reworked flu vaccine, these should be very strong vaccines and give you very strong immunity”, says Professor Hayday.

One concern is that COVID-19 may mutate, and new strains may spread much like the flu virus – which is why new flu vaccines are needed each year. This is a possibility, but there is some good news according to Professor Hayday: “Coronaviruses don't 'strain vary' anything like to the extent flu viruses do.”

What about herd immunity?

Herd immunity is achieved when a high enough proportion of the population are immune to the disease so even the people who aren’t immune are unlikely to catch it. For example, if 75% of the population is immune to COVID-19, that means if someone does have it, 3 out of 4 people they encounter will be immune, meaning they are unlikely to pass it on to anyone else.

So we don’t need the whole population to have a vaccine before we start seeing transmission of the virus drop significantly and restrictions start to relax. However, the numbers you need to be immune are very high which is why only moderate drop-offs in measles vaccination programmes in places such as New York State led to epidemic outbreaks only a couple of years ago.

Testing for COVID-19 antibodies

While we wait for a vaccine to be released, many people are choosing to take an antibody test to find out if they have already had COVID-19.

Dr Joshi says: “Although there is no conclusive evidence to suggest that people who have had COVID-19 develop long-lasting immunity that will stop them getting the virus again, a positive result from an antibody test suggests it is likely that you have had the virus, even if you don’t remember having any symptoms or feeling unwell.”

However, it is important to remember that a positive test for COVID-19 antibodies cannot tell you[vii]:

  • if you’re immune to further infection from COVID-19

  • if you can or cannot spread the virus to other people

  • when you had the virus

Check your COVID-19 antibody status today

If you think you have had COVID-19 and would like to know if you have antibodies, you can book a fast and accurate antibody test at one of our growing number of convenient locations today.

Simply order and pay for your test online, book an appointment at a time and place that suits you, and you’ll receive the results directly to your mobile within 24-48 hours. One of our in-house doctors will check your test results and send them directly to you with a personal medical report which includes any further advice and signposting you may need.

You can book your COVID-19 antibody test by clicking here: https://www.meliohealth.co.uk/product/covid-19-siemens-total-antibody, or use the chat button if you’d like talk to one of our specially trained advisors for more information.

[i] https://www.gov.uk/government/publications/update-on-immunity-to-sars-cov-2-2-september-2020

[ii] https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1275/5897019

[iii] https://www.nature.com/articles/s41591-020-0965-6.pdf

[iv] https://www.bmj.com/content/370/bmj.m3563?=&utm_source=adestra&utm_medium=email&utm_campaign=usage&utm_content=daily&utm_term=text

[v] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/921213/S0735_Update_on_immunity_to_SARS_CoV2.pdf

[vi] https://www.bmj.com/content/371/bmj.m4257?=&utm_source=adestra&utm_medium=email&utm_campaign=usage&utm_content=daily&utm_term=text

[vii] https://www.gov.uk/government/publications/coronavirus-COVID-19-antibody-tests/coronavirus-COVID-19-antibody-tests#:~:text=Antibody%20tests%20are%20used%20to,response%20to%20the%20virus

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