New point-of-care test for COVID-19 could assess need for booster

Experts have been warning for some time that lagging vaccination rates in low-to-middle income countries will likely result in the emergence of new variants, threatening efforts to contain and eventually overcome the COVID-19 pandemic.
 
The recent emergence of Delta, and now Omicron, have shown the dramatic impact these variants can have; in the space of a week, NSW has gone from recording 560 cases per day to 5715, stretching testing services and leading to concerns of an impending influx of hospitalisations and deaths.
 
The threat posed by Omicron has also increased the urgency around booster shots, leading the Australian Technical Advisory Group on Immunisation (ATAGI) to reduce the dosage interval to five months.
 
While this decision was based on emerging evidence, it does not consider an individual’s prior immunity or exposure. But a new point-of-care test, developed by scientists at the Burnet Institute and the Peter Doherty Institute for Infection and Immunity (Doherty Institute), could soon change that.
 
According to research published in EBioMedicine, the new COVID-19 NAb-test reportedly only requires a fingerprick of blood, which the lateral flow point-of-care assay can use to measure the level of neutralising antibodies (NAb) to COVID-19, with a specificity of 100% and sensitivity of 96%, within 20–30 minutes.
 
They also found that it has the sensitivity and dynamic range to distinguish between strong, weak and absent NAb levels ‘with good correlation to more labour-intensive laboratory tests’.
 
Burnet Institute Deputy Director and co-supervising author on the study, Associate Professor David Anderson said the fact that the test can work with fingerprick whole blood is ‘essential’ if it is really going to be used at the point of care.
 
‘We have [also] demonstrated that we can readily substitute different variants into the test,’ he said.
 
‘While we have not yet tested Omicron, this will be simple enough to incorporate in our test in place of the original strain or other variants that we have tested so far.’
 
The assay is also compatible with the Axxin AX-2XS reader, which is commercially available, providing the potential for fully quantitative results and linkage to laboratory information systems.
 
While there are a number of point-of-care tests available to measure the overall level of COVID-19 antibodies, this is the first test with the ability to measure NAb activity, which correlates with immune protection from serious disease in COVID-19.

With early studies suggesting that the Omicron variant may be up to 40-time less sensitive to NAb than Delta, the authors say that being able to measure NAb activity will be important to prioritise additional booster shots for people at risk of severe disease, such as the elderly and people with co-morbidities, and people at high risk of exposure, such as frontline healthcare workers.
 
Dr Kat McLean, a GP and clinical lead at a respiratory clinic/immunisation centre on the Gold Coast, said the research is a ‘positive development’.
 
But if it is to be used in general practice, she said there would need to be a clear benefit, as most GPs are currently working to capacity.
 
‘The challenges with any new test are how does that actually roll out on the ground?’ Dr McLean told newsGP.
 
‘Then it all comes back to how is that funded and supported within general practice? Or is it something that will be done within pathology companies that you would refer a patient to?
 
‘We would really have to wait and see clear guidelines as to how we would incorporate it into clinical practice.’
 
Sydney GP Dr Michael Tam, who is a member of the RACGP Expert Committee – Quality Care (REC–QC), agrees. He told newsGP that while the test is an ‘interesting innovation’, that keeping things simple in the short-term may be the best approach.
 
‘I can see the potential role it might have in prioritising vaccine delivery,’ Dr Tam said.
 
‘At the same time, vaccination is really much more of a population health intervention than individualised care.
 
‘At a superficial level, a strategic approach of “keeping it simple” of giving boosters based on simpler criteria [eg age cohorts and timing] may remain the most effective way of maximising utility.’
 
With the test currently in the prototype phase, it appears the creators are focused on the longer-term.
 
They note that the test could become a standardised option to assist in the safe reopening of borders in the context of different vaccines and the variable responses in different populations, particularly in time-critical and low- and middle-income settings where laboratory-based testing is difficult or impossible for many to access.
 
However, a limitation of conducting such tests is that even if antibody titres fall, it is possible that memory B and T cells will provide rapid and effective protection upon re-exposure.
 
‘Therefore, while antibody titres may decline, that does not necessarily mean that the individual is fully susceptible to disease,’ the authors said.
 
‘Indeed, repeat testing with an easy and rapid POC test has the potential to exaggerate fear of re-infection risk.’
 
Dr McLean says this adds to the challenge.
 
‘How do we really ascertain whether somebody has good immunity or not?’ she said.
 
‘I know that’s still being fiercely debated and there’s a lot of work going on into it. But there are more questions than answers.’
 
While Dr McLean can see a place for a point-of-care test in the longer term, she says GPs are currently trying to grapple with immunisation delivery and caring for COVID patients amid their other core work.
 
For now, she says the evidence and focus is on boosters and ensuring general practice is supported to deliver.
 
‘In Queensland at the moment we’re seeing a doubling of cases every 48 hours, so there’s the feeling that we should be getting boosters into people as soon as possible, especially our patients that have had AstraZeneca as their primary course,’ Dr McLean said.
 
‘We are absolutely at capacity … and that comes back to my comment on adding another test or another suggestion that takes time and potentially is not a straightforward test to interpret; it just adds to what we’re already doing and there has to be a real benefit for adding another step at the moment.
 
‘We don’t know what’s going to happen in another three- or six-months’ time, but I think that with this pandemic we’ve realised that it is about playing the short game rather than the long game, and we can’t drop the ball in the short-term.
 
‘So long as supply doesn’t become an issue … I think trying to get boosters into as many people as soon as possible is key.’
 
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