Antigen tests, exit strategy and communication

Wednesday, 28 October 2020 00:00 -     - {{hitsCtrl.values.hits}}

 It has always been ironic that PCR tests have been called the ‘gold standard’ when they are of vastly varying quality and prone to false positives – Pic by Shehan Gunasekara

  • Antigen tests for COVID-19 to be used in Lanka

So, we’ve just heard the announcement that we have pretty much exhausted our supply of PCR tests and the Ministry of Health has just announced ‘a new system’. The new system is called ‘Rapid Antigen Tests’ and this can provide results in as fast as 15 minutes.

The Ministry mentions WHO endorses this method, though there may be some lag in importing the equipment and providing requisite training. So, some background, lest this perplex and confound the thinking and reading public further.

These tests detect specific proteins, called ‘antigens,’ on the surface of the virus and identify people at the peak of the infection, when virus levels and contagiousness are likely at their highest. Proponents have argued this is a game changer on the basis that roll-out can be in vast numbers, and Pareto-like, we can identify those at greatest risk. India and Italy have already begun applying these as part of their national strategies.

It has always been ironic that PCR tests have been called the ‘gold standard’ when they are of vastly varying quality and as I have covered in earlier articles, prone to false positives (last Sunday Sri Lanka provided an estimate of 70% accuracy of the PCR test in our laboratories here which given how that can skew the sense of the magnitude of a ‘second wave’ is far from reassuring) and due to amplification settings (viral load). Also, as we have no other diagnostic, outside the lab (which is expensive and takes considerable time), we cannot verify those test findings very readily or affordably.

Antigen tests are faster and cheaper but aren’t as sensitive, which is largely a boon, as PCR tests can pick up even miniscule amounts of the virus.

Specialists have differing concerns, therefore. Some worry the antigen tests will miss infectious people. However, advocates say that’s a strength, as we focus on those infectious enough to be of real concern.

While currently antigen tests are conducted by professionals, companies are working on versions that may become akin to home pregnancy tests.


Different types of tests

So, we have ‘diagnostic’ tests such as PCR and ‘antigen assays’ which detect parts of the SARS-CoV-2 virus, and then ‘antibody tests’ that detect molecules that come from people who have been infected. Antibodies can take days after an infection and can linger for weeks, so aren’t as helpful in early diagnosis, but very helpful in getting a sense of overall community immunity or actual IFR (infection fatality rate).

So other than outright false positives which are there and which I’ve shown the danger of when there is relatively low population prevalence mathematically, PCR tests at higher amplification can detect small amounts of viral genetic material therefore showing a ‘positive’ also long after a person is infectious, again skewing assessments and having disastrous ripple effects on lives and other aspects of social, economic and personal wellbeing.

Scaling up PCR tests has also just been difficult and unsuccessful even in the US and UK. Antigen tests are less invasive, easier to administer, and can deliver results in less than 30 minutes. They also don’t have to be processed in a lab.

Antigen tests have been successful in 95-100% of cases within a week of the onset of symptoms, but that drops to 75% more than a week after symptoms. That however, isn’t worrying, as the person is in that instance, actively symptomatic and being treated. 

Virologist Marion Koopmans at Erasmus University Medical Centre in Rotterdam, Netherlands, says, “The question is, what is the safe limit? We need to agree globally the viral load where we are aligned the person is no longer infectious.” That will help validate rapid tests.

Strong evidence suggests people are no longer infectious eight to ten days after showing symptoms. Michael Mina, infectious disease immunologist at Harvard T.H. Chan School of Public Health in Boston, Massachusetts is a vocal advocate of antigen tests.

Asked about the challenges of people having low levels of the virus at the start of the infection, he replies the answer is frequent testing, multiple times a week (easy to do with these), because if symptoms are building, the amount of virus in throats and noses rises within hours, he says.

Having used statistical models to assess this strategy, in a preprint that came out in September, he and his colleagues suggest that testing people twice a week with antigen tests would be more effective in curbing the spread of C-19 than more ‘complex’ tests every two weeks, with lag time in results, and potential distortions. These findings have been replicated in another parallel study looking at safely reopening university campuses.

The key is to identify those most at risk of getting sick and infecting others not just ‘spotting’ people who have been ‘infected’ in some way, to some degree, at some time. The rapidity, allows for rapid response, without persecuting scores of people who for two weeks have their lives and livelihoods seriously compromised.

If symptoms seem to develop despite a negative antigen test, then a PCR test could be used as a follow up, which is the approach India is taking, also recommended by the CDC in the US and WHO. When the August surges hit India, the antigen tests helped in picking up and targeting the increased number of cases. The US FDA antigen tests have a greater sensitivity than the Indian tests and come from Abbott Laboratories.


GMOA exit strategy

This too was just presented. I will not analyse this in detail as you can readily read it, clearly well intentioned, well thought through. However, we should stop using ‘hammer and dance’ references as multiple months of 24/7 outright curfew unfortunately clung to in the spring when fatalities were nominal and so were cases, has exhausted our ‘hammer’ options if we want to keep the economy afloat and not visit far greater personal, medical, educational and economic hardship than a viral interloper that has not come close to being a real health variable when we have 12,000 deaths from normal causes of mortality each month in Sri Lanka.

Saying the cases have grown ‘exponentially’ or ‘diabolically’ (another characterisation used later) is hyperbole. Exponential means continually growing as per some percentage. When we have daily tallies ranging from 500 to 167 to 198 to 353, to one vertiginous spike (to date) of 866, we cannot call this ‘exponential’ growth. 

We can say that unlike past surges, mainly from the Navy and rehab centre cluster, here, because people went out from one superspreader environment and then through the fish markets and local networks, there are multiple clusters, larger aggregates therefore, and contact tracing is certainly more complicated.

Happily the GMOA document acknowledges the lack of long-term viability of ‘lockdown,’ though still ‘lockdown’ is not the same as ‘curfew’ (something we still can’t seem to fully distinguish on these shores), and the document does take aim at protecting life and liberty overall along with health. We can all salute that, as they are symbiotic, inextricably linked!

I do think we may have to, with the introduction of the antigen tests, be able to relieve much of the stress on the quarantine network, whereby those with mild symptoms (but actual symptoms) can go to patient monitoring centres (current quarantine centres) if necessary, and only those with serious symptoms or at high risk or those who cannot be housed can go to a quarantine centre or specialised COVID Management Hospital.

Overall, a step in the right direction, though we need the antigen tests to make sure ‘positive test results’ that aren’t ‘cases’ are not clogging up capacity and capability and unnecessarily impinging on people’s lives.



Breaking news: A 17th fatality in Lanka has been stated related to COVID. I put this under ‘communication’ as to me it is ‘miscommunication’. This was a 41-year-old person suffering from ‘cirrhosis’ (late stage of liver scarring from hepatitis or chronic alcoholism almost always, not COVID). 

So that this person ‘also’ tested positive for COVID does not mean they died from COVID. Surely some protocol needs to be in place to underwrite these potentially distorting classifications? For information, the chance of a 40-year-old being hospitalised, without pre-existing conditions, from COVID, is below 4%. 

By definition cirrhosis goes with ‘immunity compromise’ and the fourth most common infection that results we are told as a byproduct is pneumonia. The original name for C-19 was NCIP (novel coronavirus-infected pneumonia). Surely, we also need to clean up how are we cataloguing deaths and communicating them?

People’s lives are on the line, and not from the contagion primarily. One test and they can be sent off, away from family, from earning a living, utterly helpless, feeling like prisoners, for weeks. There is a psychic and emotional toll here.

We’ve managed the current outbreak quite astutely, zonally, with data, but our communication seems all over the place. We keep saying we aren’t going to add to the state of affairs as of Friday evening, and then numerous places are shut down all over the week-end, almost open and then not open, often on the basis of one solitary person or for other reasons not shared, and so the perception, psychologically, is complete inability to plan, to staff businesses, to conduct life or educate children (who are at virtually no statistical risk so the decision basis gets more curious), or even to get needed necessary public services. 

The hotel industry, a bulwark of the national economy, barely hanging on thanks to local tourism has again been paralysed. We cannot be so scared of ‘test results’ as to keep doing this to ourselves, when so few people get infected or actually perish if they do, even in the more vulnerable demographic, something we can clearly state on global data.

And even where not ‘shut down’ the panic communication, without balance, or without reassuring a populace terrified by global media panic, that this is far from being the world’s greatest mortality threat, much less Lanka’s, leads people to cower at home. Some are being good citizens, limiting travel and movement and interaction, but this kills businesses too, when it starts to verge on hypochondria and gets perpetuated for weeks. 

In Europe despite clamour of cases, there is virtually no excess mortality (cases keep mushrooming, but these are again not even ‘cases’ just ‘positive tests’) in the last two weeks there has been only a very nominal increase led by two to three countries. 

EUROMOMO will confirm that for anyone interested. US COVID illness trend despite surging cases where testing has been significantly ramped up (as in Lanka, when you massively test more, you will get more ‘results’ sprouting even if most are asymptomatic and most people’s immune systems are handling the situation just fine), still has persistently and consistently low incidence of C-19 illness using ER visits from most recently available data. Less than 6% of US hospitalisations are COVID related as of this writing.

Could we please give some game plan for restoring shut down districts and zones to normalcy, agree thresholds for further circuit breakers, and as the Cabinet said, reported 26 October, “It was discussed that the best solution was for people to live maintaining guidelines by the health sector.” Amen!

But please understand we must tell people, “follow guidelines AND rebuild Lanka, trust your medical professionals, leaders AND your God-given immune system, then let’s rally that and restore the recovery momentum”. The alternative is we shiver and cower and while nominally ‘open,’ we are destroyed when our vitality is usurped by a barely functioning ‘routine’.

Let’s build on the wisdom of the current response, and now that we see, thousands of cases aren’t popping up disconnected to the clusters (or even hundreds or even multiples of 10), let’s get the antigen tests, relieve the pressure on the current system as outlined, and rekindle again Sri Lanka’s so often demonstrated, never far away, national resolve.

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