One of the measures that is discussed these days is the convenience of using the so-called “immunity passports” or “risk-free certificates” that prove that a person has already passed COVID-19 and, therefore, could go to work and circulate without danger of contagion or being infected.
It is a very controversial proposal because, in addition to the ethical implications of the use of this tool, current knowledge about SARS-CoV-2 is very limited, and it will take months until all the details about how it infects are known. the virus, how it spreads and, in this case, how is the immunity generated after passing the disease.
Currently, it is not known if the antibodies generated by the body to overcome the virus infection are sufficient to guarantee that that person is immune to a new infection and, in case of having this supposed immunity, we also do not know for how long they are protected: some weeks? Months? Lifetime?
The World Health Organization (WHO) has recalled all this in a statement and, in addition, has specified that current antibody tests are not accurate enough. ” All this can create confusion among people, leading them to ignore public health advice and causing transmission to continue ,” says the institution.
The famous ‘quick tests’
The diagnostic test that is commonly used to find out if a person is infected with SARS-CoV-2 is PCR, which allows detecting the genetic material of the virus in the sample. It is a very reliable test, but it requires time and having adequate equipment and qualified personnel to perform the test.
In recent weeks we have heard about the famous ‘serological tests’, which are based, not on isolating the genetic material of the virus, but on locating the antibodies generated by the patient in response to infection from a blood sample. They are faster than PCR but less reliable, and also the information they offer is different, since the antibodies begin to be produced from the sixth day from the onset of symptoms, so no recent infections are detected.
Due to the emergency situation, these rapid tests are being used around the world to help manage the crisis, but health authorities stress that the results of these tests should be taken with caution. The urgency of the situation has caused protocols and tests that generally take months or even years to be developed in a few weeks and, as an article published in the journal Nature indicates , “most of the kits have not been subjected to rigorous tests to guarantee they are reliable, and no country seems to currently have a validated antibody test that can accurately determine whether an individual has had COVID-19 . “
For this reason, rapid detection kits are being used in the health field to detect possible outbreaks early and to act quickly, but their use is not recommended on a personal level , nor that pharmacies or companies begin to carry them out en masse, as they can lead to erroneous interpretations.
How long does immunity last?
In addition to how difficult it is right now to know who has had the disease, the question of determining how long one is immune to a new contagion remains in the air.
” Most of the studies carried out show that people who have recovered from the infection have antibodies against the virus, ” explains the WHO. “However, some of these people have very low levels of neutralizing antibodies in the blood, suggesting that, in addition to antibodies, cellular immunity (a form of immune response mediated by cells called T lymphocytes) may also be critical for the recuperation. Until April 24, 2020, no study has evaluated whether the presence of antibodies against SARS-CoV-2 confers immunity to subsequent infection by this virus in humans ”, he concludes.
In addition, it is also necessary that the tests carried out have the ability to distinguish between the immunity conferred by the other six coronaviruses that affect humans, four of them cause the common cold, and SARS-CoV-2. “People infected with any of these viruses can produce antibodies that cross-react with antibodies produced in response to infection with SARS-CoV-2,” says the WHO.
In summary, the studies and tests carried out by rapid tests are necessary, as they help detect outbreaks early and get an idea of the percentage of people with detectable COVID-19 antibodies, but most are not designed to determine if these people they are immune to secondary infections.
It is very dangerous to assume that, if you have passed the disease, you are already immune to a second infection, because this can lead these people to ignore public health advice. “Therefore, the use of such certificates may increase the risks of continued transmission of COVID-19,” concludes the WHO.
