Why didn’t I get covid despite living with someone who tested positive? | Society

“My partner had covid and, even if I slept with her, I didn’t catch it”. This sentence is pronounced by Ana, 37, but it is repeated over and over again with multiple variations: children who do not infect their parents, grandparents to their grandchildren or very close contacts with no apparent transmission. Despite being a highly infectious pathogen, SARS-CoV-2 it is not infallible. Many reasons, some certainly to be discovered, explain why it is common for someone in the same house without too strict measures to get sick and someone who does not test positive.

It’s not new. Already from the first months of living with the covid it occurred that there were much more transmitting people than others, as well as individuals who seemed naturally immune: no matter how close they were to the virus, they didn’t catch it. Each person’s immune system works differently and, after seven waves (in Spain) and millions of injected vaccines, each person’s can be in a very different moment which makes their body’s reaction to contact with the virus different.

It is not uncommon that when the pathogen enters the body, the immune system rejects it and does not lead to the accumulation of a sufficient charge to give a positive antigen test, which are the ones you can buy at the pharmacy. This can also happen with the symptoms involved, which would be the reaction caused by the immunity to defend itself against the virus.

Another case: Enrique, 76 years old and with the fourth dose of vaccine just administeredHe has had cold symptoms for a few days and leads a completely normal life with Clara, his wife, even with the second memory of the recent injection. After a few nights with a cough, he takes the test and it comes back positive. Clara does not develop even a slight sign of the disease. Have you passed the infection without realizing it? It’s possible. Maybe she was the one who infected Enrique too. Or that she never had it.

“When the vaccine is very recent, it is possible that the specific neutralizing antibodies have been able to prevent the increase in this viral load,” explains Marcos López Hoyos, president of the Spanish Society of Immunology.

Vaccines don’t prevent infection, but they do reduce the chance, especially in the weeks and months following infection. Statistically it is not uncommon that, with the same doses and exposures, some people become infected, with or without signs, and others not. And this happens with vaccines, but also with the natural immune response, which is more effective if the disease has passed, and even more so the closer that event is.

José Antonio López Guerrero, professor of microbiology at the Autonomous University of Madrid, explains that there are many factors involved in the contagion: “If you are vaccinated (or previously infected), when you get infected again through the oropharyngeal or nasopharyngeal routes, your The immune system can be armed very efficiently, trigger an effective response and cause symptoms before you even have enough viral load to test positive for an antigen test – or even never test positive at all.

There may also be genetic variability that makes some people even immune to covid. No mutation has been discovered that makes it possible, but scientists don’t rule out that it may come to light over time, as has happened for other diseases, such as HIV or malaria. This might explain the cases of some individuals who, despite having been close to the virus wave after wave, have never tested positive.

To all these factors, Juan Carlos Galán, head of virology at the Ramón y Cajal hospital in Madrid, adds another: the real ability of the tests to detect the virus. To check if it has reached the body, a home antigen test would not be worth it; a PCR would be necessary, capable of identifying even minimal viral loads. Those of pharmacies, while being a good predictor of the disease in people with symptoms, have a margin of error, which increases in those without symptoms. And, in many of those sold, their reliability may decrease with new variants, as they may lose effectiveness as the virus evolves. “They’re not that well researched [como las PCR] and sample taking can have a lot of variability,” says Galán.

What to do before a contact?

A frequent situation, which occurred in the examples mentioned, is discovering that someone in the family or very close contacts has tested positive after several days of symptoms, when there has already been a lot of coexistence. At that point does it make sense to start isolation or measures to prevent transmission or is it die cast? Here too there are no univocal answers and everything moves in the realm of probability and precaution.

López Hoyos believes that at least some precautions, such as wearing a mask, should be taken to avoid spreading the virus into the environment. “It’s positive at the moment, it could have a higher viral load and I would try to have some protection,” he says. His colleague López Guerrero agrees and this is what he did in the two cases in which he experienced a similar situation: “That person can still be infectious-contagious and it is better [hacer algo] later than never My wife tested positive while we were together and isolated herself that day. And six months later I tested positive and she, who was at her daughter’s house when I took the test, stayed there for a week. Neither she infected me, nor I her.

Galán is more decisive: “Transmission is a probabilistic event and, until proven otherwise, the uninfected individual should avoid further increasing the chances of exposure. Therefore, after close contact, the exposed individual should be monitored, tested and further exposure at the source avoided.”