Like the sound of a Covid-19 ‘immunity passport’? Here’s why it’s pie in the sky

Muiris Houston: So far, there’s no evidence surviving coronavirus guarantees immunity

Many human infections with other viral pathogens, such as influenza virus, do not produce a durable immune response.

Many human infections with other viral pathogens, such as influenza virus, do not produce a durable immune response.

 

As the Covid-19 pandemic rolls inexorably onwards, many of us are trying to get some handle on the future shape of our lives. When can we experience a normal wedding ceremony again? A full wake is part of the funeral process for many in rural Ireland; can anyone say with certainty when we can return to the time-honoured traditions of mourning? And with such a widespread diaspora, when can families safely plan for those regular reunion trips which bring such joy and connection?

There has been some discussion, especially on social media, of the merits of so-called “immunity passports” as a way to control the risk of Covid-19 infection. Also referred to as “immunity certificates” or “immunity cards”, the idea is that such documents would be issued to those who have survived Covid-19 and tested positive for antibodies to SARS-CoV-2 (the new coronavirus that causes Covid-19). Survivors with a presumed acquired immunity would be allowed to resume social interactions, on the basis that they were neither at risk of infection nor of spreading the disease.

Sounds promising?

No, actually, it’s a disingenuous and unhelpful proposal with no scientific basis.

To explain, join me in a superficial journey through the human immune system.

There are two elements to how our bodies react to viral infection. One is called innate immunity; it occurs rapidly after infection enters cells and involves the invader being tackled by natural killer cells. The other is called adaptive immunity and is generally a slower response. Antibodies now take over, which prevent infection by stopping the virus binding to a receptor. However, once the virus gets into the cell, the immune response involves cytotoxic T cells killing the infected cell.

Incomplete picture

Even with this cursory examination of our immune system, we can see the response to a viral infection is complex, multilayered and time dependent. Measuring just one element – the level of antibodies – will, at best, give us an incomplete picture of immunity.

Dr Mary Keogan, consultant immunologist at Beaumont hospital and national clinical lead in pathology, gave a remote video update on Sars -CoV-2 testing to members of the faculty of pathology of the Royal College of Physicians in Ireland recently.

Far from endorsing immunity passports, her talk made it clear there is no evidence to correlate Sars-CoV2 antibodies with future protection from infection.

“The jury is still out on whether there is any protective immunity following [Covid-19] infection,” she told doctors. So in advance of extensive research, giving guarantees about reinfection with Covid-19 based on antibody levels is false medicine.

What about after a vaccine against Sars-CoV2 becomes available – will it be possible to measure antibodies to the virus after a person completes a course of vaccination in order to assess the safety of air travel for example?

Again uncertainty prevails: extensive testing after the vaccine has been administered to thousands of people will be needed to answer this question.

In a report last week, the Health Information and Quality Authority (Hiqa) noted: “Evidence for other types of serious coronavirus infections, such as SARS-CoV-1, shows that the antibody response is maintained for one-to-two years after initial infection and decreases thereafter”.

However, whether this limited immunity will occur among individuals after they have recovered from Covid-19 is uncertain. Many human infections with other viral pathogens, such as influenza virus, do not produce a durable immune response.

An opinion piece in the Journal of the American Medical Association (JAMA) concluded that amidst the uncertainty of this public health crisis, “thoughtful and rigorous science will be essential to inform public health policy, planning, and practice”.

Faced with the expected plethora of commercial testing products flooding the market, caveat emptor will be the order of the day.

And for those of us straining at the leash to visit family abroad, festina lente (make haste slowly) is our only option.

mhouston@irishtimes.com

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