The rise of the sixth wave has triggered the sale of self-diagnostic antigen tests against covid. In November, when the epidemic curve began to emerge again, more than 1.3 million tests were sold in pharmacies, 115% more than the previous month, according to data compiled by the health consultancy, Iqvia. And the buying trend continues to rise in recent weeks: the proximity of the Christmas holidays and the rise of the new wave – the incidence is 442 cases per 100,000 inhabitants at 14 days – keep the rage with these self-diagnostic tests that While they can detect positive cases, they are not foolproof. Epidemiologists warn that these tests can give false negatives and warn of the false sense of security that they generate: this test does not exempt from compliance with other measures, such as the use of a mask indoors and in crowds, social distance and ventilation.
Antigen tests have been dispensed in pharmacies without the need for a prescription since last summer. These tests identify the presence of virus proteins and, according to the Spanish Agency for Medicines and Health Products (AEMPS), there are about twenty devices on the market. The consulting firm Iqvia has recorded that, in 2021, 8.7 million tests have been dispensed in pharmacies, but sales fluctuate along with the epidemic curve. Thus, although in July and August, during the fifth wave, 1.5 and 1.9 million self-diagnosis tests were sold, respectively, in September and October —when the epidemic curve fell and the circulation of the virus subsided— sales fell to less than a million a month. Now, with the rise of the sixth wave, the approach of Christmas and the threat of the omicron variant, which experts fear is more transmissible, the collection of self-diagnostic antigen tests has returned.
In fact, along these lines, the president of the Community of Madrid, Isabel Díaz Ayuso, announced two weeks ago a free test for each inhabitant “so that in case of social gatherings, they are done safely,” he said. But the epidemiologists consulted are suspicious of this massive use of self-diagnostic tests because it can lead, they warn, “to a false sense of security.”
Daniel López-Acuña, former Director of Emergencies at the World Health Organization (WHO), recalls that “they do not have the same specificity [capacidad del producto para reconocer la ausencia del marcador vinculado a la enfermedad] and sensitivity [la competencia del test para detectar la presencia de ese marcador] than PCR ”. The expert asks for caution: “We cannot sell that it is a resounding yes or no. And it cannot be the excuse for not getting vaccinated, not having the covid certificate in order or exempting us from the use of a mask, distance and ventilation in groups of non-cohabitants ”.
Antigen tests are not foolproof. They can give false negatives and false positives. Not surprisingly, the Alerts Report of the Ministry of Health already pointed out last summer that a positive in the self-diagnosis tests will be considered a suspicious case and will have to confirm the infection with another diagnostic test. But there is no one to monitor or control the test result. Individual responsibility rules.
According to the Alerts Report, pharmacies will have to provide clear information on how to proceed if the result is positive, but the final decision is made by the user. Some communities, says the General Council of Pharmacists, have deployed a protocol to facilitate the possibility of registering the test result from pharmacies, whenever the citizen wants. What the Alert Report does indicate is that if a person tests positive in these self-diagnosis tests, they will have to initiate home isolation and contact the health services (through the channels established in their community) to confirm that it is, effectively, from a coronavirus infection.
The document of the consulting body of Health also warns, on the other hand, that “negative results do not exclude the possibility of infection.” This is what happened, in effect, in the massive outbreak of health workers in Malaga, where all those who attended the dinner had taken an antigen test and it turned out that there were false negatives: more than 80 people were infected. Also in the three music festivals held last June in Catalonia: antigen tests were carried out before entering, but more than 2,000 attendees were infected, according to a study by the Government.
So what is a self-diagnostic antigen test for? It is one more protective barrier, like the mask or social distance, insists Óscar Zurriaga, vice president of the Spanish Epidemiology Society. “The message has to be that all measurements are important: take the test, but keep all the others. Basing everything on a single measure is a bad idea, “says the epidemiologist.
In practice, the best performance of these tests is achieved in symptomatic people, in the first five or seven days after infection. But the predictive value of the test “depends a lot on the epidemic situation and the symptoms,” says Salvador Peiró, epidemiologist at the Foundation for the Promotion of Health and Biomedical Research of the Valencian Community (Fisabio). “If you have symptoms and you test positive, you are almost certainly positive. If you have symptoms and you test negative, it is preferable that you confirm it with a PCR because this test only detects high viral loads and if it catches you at the beginning of the infection, in the incubation period, it may not detect the viral load “, says the specialist . But things “get very complicated” with asymptomatic people, because there can be false positives and negatives. Peiró points out, however, that the greater the circulation of the virus, the less probability of failure.
Doesn’t avoid all risks
However, the Fisabio epidemiologist insists: “It is a mistake if you take this measure to replace the others. A test rules out some risks, but it does not avoid them all ”. And it warns that the mishandling of the tests allows the circulation of the virus. “For example, if you’ve been in close contact, the antigen test gives you negative and you don’t isolate yourself. If you’ve had close contact yesterday, it will take four days for you to test positive. In the first four or five days of incubation there is not enough viral load for the tests to be positive ”. In addition, there may be problems when doing the test: the effectiveness of the tests has been proven in laboratory settings, but people in your home can do the test wrong, contaminate the sample or make a mistake in the procedure and alter the result. of the test.
López-Acuña insists that “we must stop selling self-diagnostic tests like the silver bullet because it does not give the definitive and forceful answer.” And remember that, in addition to a skyrocketing incidence in Spain, “uncertainty with the omicron variant” continues, the new lineage of the virus that has put the world on alert and that, according to the first indications, it could be more transmissible than the variant currently dominant (the delta).
George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.