A study shows in infected patients that there are memory cells in the bone marrow in a “persistent” way and can produce antibodies when necessary
The memory cells in those who have passed the infection mature and improve over time, for at least a year
Infected people who get vaccinated are much better protected against virus variants, even with a single dose
Immunologists have long warned of this, and the studies that are being done are corroborating it, as time passes: the immunity that our body generates against the SARS-CoV-2 coronavirus lasts much longer than previously thought at the beginning of the pandemic. Both the antibody and the cellular one. And the latter, above all, is very powerful. Now, two studies have just published confirming results.
The conclusions of both studies suggest that natural immunity against covid can last at least one year. It is the maximum time that it has been possible to study, it still has not passed more. But It has also been seen that it improves over time, especially after receiving the vaccine. Therefore, as it is in addition to cellular memory, it is possible that this good answer can last longer: many years, or even a lifetime.
Investigations that Immunity evolves very differently in those vaccinated who have passed the COVID and in those who have not. Those who have passed the infection and are vaccinated have a stronger immune response than those vaccinated who were never infected. And it has its logic. Fighting a live virus is not the same as fighting a single of its proteins, which is the response induced by the vaccine. But we go in parts.
Memory cells that “persist” in the bone marrow
In one of the studies, published this week in Nature, immunologists from the University of Washington have seen that memory-preserving cells of the virus (B cells) persist in the bone marrow and can produce antibodies when necessary. That supposed to be like we have a small factory of antibodies installed in the marrow, inactive but latent. There our body has a kind of medical history where all the pathogens that infect us throughout life are recorded.
A factory that, from there, continues to produce antibodies for decades every time our body needs them, once the acute infection has been overcome. Antibody levels drop sharply, but these cells don’t. “Consistently, they detected circulating memory B cells at rest directed against protein S in convalescent (previously infected) individuals ”, we read in the study.
The B cells are the ones that are quickly activated and produce the antibodies when we first encounter the virus. What this study now confirms is that those that “settle” in the marrow “are a persistent and essential source of protective antibodies”. Something that leads the researchers to ensure that “people convalescing from SARS-CoV-2 – who passed the infection – have a significantly lower risk of reinfection.”
Antibodies decay, B cells remain stable
But how did they get there? Analyzing blood samples from 77 people who had covid, who were followed closely every three months. They started a month after his infection. 71 of 77 had a mild infection, only six had been admitted.
For the study, they obtained Bone marrow samples from 19 of the participants seven months after infection. 15 of them had memory B cells detectable. In addition, five of the participants donated bone marrow samples 11-12 months after infection. And what did they see then? That the number of memory B cells remained stable during that time. They stay there, stable and ready to act when needed. Therefore, the key role played by cellular immunity in this coronavirus is confirmed, as experts have pointed out for months.
Levels In contrast, antibodies from all participants decreased rapidly four months after infection (something that previous studies already pointed out) and they continued to decrease slowly and gradually “during the next 7 months”, although “remaining detectable for at least 11 months after infection.”
There is one more thing. On four of the 19 participants who donated bone marrow could not detect those memory B cells, which leads the researchers to further point out that infected people should be vaccinated. One dose is enough for them, as has already been proven, but they have to be vaccinated.
Memory cells that mature and improve over time
The study was carried out in 63 people who had mild covid, which were “evaluated at 1.3, 6.2 and 12 months after infection.” 26 of them, 41% had also been vaccinated with the first dose of Moderna. The researchers analyzed the blood of the 63 participants and found that both neutralizing antibodies – those that block the virus and prevent reinfection – and memory B cells “They remain relatively stable for 6 to 12 months.” And they also saw important differences between the vaccinated and the unvaccinated.
Vaccinated infected, more protected against variants
One year after infection, the neutralizing activity of the antibodies in the unvaccinated was lower than in the vaccinated. Above all, a significant loss of neutralizing antibodies against South African variant, although this would be to some extent predictable, because it is the variant that best eludes this immune response. The vaccine it significantly amplified the levels of antibodies, and also enhanced their neutralizing capacity. That is improved this response in quality and quantity.
As time passed and memory B cells continued to mature, the antibodies they produced developed the ability to better neutralize the variants. This shows, they say, that people who have passed COVID and then received the vaccine will have extremely high levels of protection against emerging variants, even without receiving a booster dose.
The memory B cells produced in response to infection, and later enhanced by vaccination, are so potent that they thwart even variants of the virus, eliminating the need for a second booster dose of the vaccine.
In the study they explain it like this. “The data suggest that immunity in individuals who have passed the covid will be very long-lasting and that those who receive the mRNA vaccines (Pfizer or Moderna) will produce antibodies and memory B cells that should protect them against circulating SARS-CoV-2 variants ”.
Michel Nussenzweig, the immunologist who led the study, warns in the New York Times that “People who are infected and vaccinated afterwards have an excellent response. And hopefully it will last a long time“Those who have not passed the covid, however, may need that second booster dose of the vaccine.
Lombardy confirms the longevity of the answer
There is another study, published this Friday, that corroborates all this in one of the first scenarios where the pandemic raged: Lombardy. It was the first ground zero of the covid in Europe. Well, now it has been proven that, after a year, the immunity of the infected then remains very high.
“Reinfections are rare and patients who have recovered from covid have shown a lower risk of reinfection. Natural immunity to SARS-CoV-2 appears to confer a protective effect for at least one year, which is similar to the protection reported in recent vaccine studies, ”the researchers conclude.
The only thing they could not determine in this case is whether that immunity is still as high when facing the variants of the virus. “The study ended before the SARS-CoV-2 variants began to spread. and it is not known if the natural immunity to the original virus will also protect against the variants ”, they warn.