Antibodies, the molecules that our immune system generates to deal with pathogens such as SARS-CoV-2, are a key piece in the defense against the contagion of Covid-19.

They also play a key role in creating the long-awaited group immunity that can end the pandemic, so lThe survival of these in the body is a very relevant piece of information to know the effectiveness of vaccines that are in the final stretch of their development.

Two new studies published this week defend that the antibodies generated by people who have been in contact with the virus disappear after a few months – between two and three – although they are more durable in patients who have suffered a more serious illness.

“The main conclusion is that, after the first wave, there was still no evidence that the vast majority of the country’s population had protective immunity”, explained in a statement Graham Cooke, one of the authors of a study on the prevalence of antibodies in the United Kingdom between June and September, carried out by Imperial College London and Posted this Tuesday.

In general, they found that the level of immunity dropped by 26.5% during that period, while the decrease in protection was 39% for those over 75 years of age.

Another study also carried out in the United Kingdom, in this case by scientists from King’s College and published Monday in the magazine Nature, reached a similar conclusion, although it added that “a higher viral load could lead to more serious disease and generate a stronger antibody response.”

This study suggests that “vaccines should be aimed at provoking the creation of antibodies similar to those generated in severe cases” and adds that additional doses may be required after those initially planned.

The question of the duration of antibodies against Covid is one of many aspects of the disease caused by SARS-CoV-2 that are still under investigation and on which there is no clear scientific consensus.

Two other recent studies – one published in mBioand another already accepted by Cell– They have concluded that antibodies take longer to disappear or do not disappear in the time that we have been in the pandemic and the results vary considerably depending on the techniques used to detect them.

The absence of antibodies does not equate to a lack of immunity

In any case, it should be borne in mind what microbiologists do not tire of repeating and also defend these two articles: the absence of detectable antibodies does not have to mean that people who have had the disease are not immunized and, as proof, they are points to the absence of a significant number of reinfections.

Till the date, there are only half a dozen proven cases worldwide that experts attribute to alterations in the patient’s immune system.

“The detection of IgG antibodies is not a sine qua non condition to be protected against infection”, declares José Antonio López Guerrero, director of Neurovirology at the Autonomous University of Madrid. “The ability to generate both humoral and cellular immunity can be there even if it is not detected in a serological test and be effective for years.”

The reason why the absence of antibodies is not synonymous with lack of immunity is in known as memory cells: B and T lymphocytes. “If you have active memory cells, as soon as you come into contact with the virus again, you would produce antibodies again and that second contact would be totally asymptomatic,” says María Tomás, spokesperson for the Spanish Society of Infectious Diseases (SEIMC).