The rebound in coronavirus cases confirmed by PCR has slowed the return to normal after the return of the holidays. And every day the fear of a new confinement grows stronger. In these circumstances, the commercialization of the COVID-19 antigen test is good news to stop the second wave. In fact, this is how it is collected by some of the most prestigious medical journals, Nature among them.
The news comes now, when more than 10,000 cases are reported daily in Spain. Although until recently many cases were young and asymptomatic, hospitals are already beginning to saturate again and deaths are increasing. Outbreaks occur in many different places: in families who have held events, in schools and universities, in workplaces, etc. In addition, many more diagnostic tests can now be done , which was not possible during the first wave of the pandemic, back in March and April.
How is a COVID-19 antigen test done?
PCR tests are annoying for the patient, expensive (€ 100), take at least 24 hours to give results, require specialized laboratories and overestimate who is contagious. In recent weeks, all these disadvantages can be solved with the new SARS-CoV-2 antigen tests.
Like the rapid antibody tests, these are 5 cm rectangular plastic sheets. The antigen test, however, does not use a capillary blood sample, obtained after pricking the finger. In this case, a swab is used to collect the patient’s nasopharyngeal exudate – as in PCR – and the result is available in less than 30 minutes. Each antigen test costs less than € 5 and is done together with the patient, without requiring any laboratory instruments. All advantages.
More importantly, the apparent lower sensitivity with respect to PCR is actually an advantage, because it better diagnoses the period of contagiousness, which today we know does not go beyond 7-10 days after the onset of symptoms. CRP, on the other hand, can be confusing, since it can be positive for several weeks after symptoms resolve, when the patient is no longer contagious. The result reflects, by then, a “genetic garbage” or residual.
A characteristic of the infection by the new coronavirus is that the contagiousness of the infected begins 2 days before the symptoms begin, which makes it very difficult to isolate cases and prevent infections. It is estimated that almost half of all infections could occur in the incubation phase. Hence how difficult it is to stop the transmission of the virus, since the symptoms have not yet appeared in those infected.
To make it more difficult, it is estimated that up to 80% of those infected will be asymptomatic , so that their period of contagion will go unnoticed, which is good for them but does not alert them that they can transmit it to others.
Indications of the COVID-19 antigen test
It is foreseeable that the first generation of COVID-19 antigen tests will improve rapidly, so that in the coming months they will become similar to pregnancy tests. We can predict that they will be sold in pharmacies in packages of 25-100. That can be done at home and as many times as you want. That will be used before traveling, going back to school or university, attending family, professional or leisure meetings, etc. And, of course, as long as there has been a risk exposure or compatible symptoms. The easy identification of those infected will allow them to be quickly isolated and prevent them from transmitting the coronavirus to others.
The availability of the new antigen tests will not prevent continuing with social distancing, the use of masks and the performance of activities in open spaces. But it will help to select who should and who should not do isolation and quarantine.
On the other hand, antigen tests are the best tool to identify and isolate supercontagators, those that produce the largest coronavirus inocula. If antigen tests are generalized, they may allow the recovery of a more normal rhythm of activity and avoid social and labor paralysis due to uncertainty and confinement.
In any case, only the protection derived from an effective vaccine will put an end to the pandemic. Even in the best scenario and without unexpected shocks, the benefit of vaccines against COVID-19 will not be seen before next summer. Therefore, we are forced to live with the COVID-19 pandemic for several more months. Advances such as the one represented by the new antigen test are very welcome.
Vicente Soriano, Faculty of Health Sciences & Medical Center, UNIR – International University of La Rioja
This article was originally published on The Conversation. Read the original.
