As the COVID-19 vaccine spreads, there are three big questions. First, can someone who has been vaccinated still spread the disease? Second, will the vaccine still be effective as the virus itself develops? And third, how long does the protection of the vaccine last?
There are answers to these questions in our immune systems. And the answers are not simple because our immune systems are both extremely capable and very challenging to predict.
Let’s start with the first question, about whether people who are vaccinated can still spread the disease. Marion Pepper, a psychologist at the University of Washington, says it’s not just an open question for this vaccine, but for vaccines in general.
“I think it’s hard to say because we’re constantly plagued by various pathogens and we don’t know when your immune system is responding,” she says. we have diseases that do not make us sick, so we do not know about them, but we could spread a disease.
When a person becomes infected – or vaccinated with a vaccine – the immune system prepares to make antibodies that specifically target the virus. Over time, these antibodies become naturally depleted. But the immune system still remembers the virus, and if it reappears, cells become activated and start building up a new batch of antibodies. However, that process can take three to five days.
In the meantime, a virus can begin to reproduce in the body.
“It’s a bit of a race between the immune system and the virus,” said Dr. Michel Nussenzweig, a Howard Hughes Medical Institute researcher at Rockefeller University.
If the immune response starts quickly, there would be very little virus. Your ability to spread a disease “really depends on the amount of virus you carry,” Nussenzweig says.
A person’s immune system seems to have won that arms race, but scientists still don’t have the data to say that with confidence. That’s why people who have been vaccinated have the right to wear a mask and take other steps – until that is resolved.
Another wild card here is that you have a population of T cells called your lungs and nasal passages, which are primed to identify virus-infected cells. These types of T cells are much more difficult to study, because they live inside nappies, so scientists studying blood samples do not see them.
Because these T cells expect an immediate response, they may help fill the gap between the time you get the infection and the time your immune system can respond fully. the antibodies.
“In the flu, those T cells that are rooted in the strain can have a major impact on limiting the disease,” says Stephen Jameson, a psychologist at the University of Minnesota medical school. But whether they perform so well in COVID-19, “we don’t know enough yet,” he says.
The second question, as to whether the vaccine will remain effective even as the virus grows, is more difficult to answer. So far scientists are not too worried about the prevailing rays of the virus that are spreading around the world – vaccines are likely to still work against them. But the virus will continue to thrive, with uncertain consequences.
“Even though everyone worries about a virus developing, cellular responsiveness to B memory grows over time,” Pepper says.
B memory cells are an important part of the immune system because of the memory of an infection. These move in your bone marrow, and are ready to move into antibody-producing cells if the virus they “remember” reappears in the bone marrow. your body.
But they don’t remember just one specific antibody that has worked against a virus in the past. They can also randomly generate new antibodies that are similar, and potentially more effective against a type of virus that your body has never seen.
“This is the only time in the body where a mature cell deliberately mutates mutations into the DNA,” Pepper says.
But amazing as this system is, it has limitations. Viruses that undergo major changes from one year to the next, such as the flu, can invade this system. That’s why you need a fresh look of flu every year. The COVID-19-induced coronavirus moves much more slowly than the flu, but it is not yet clear whether B memory cells will be flexible enough to monitor the virus permanently.
Finally, the question is how long a vaccine lasts.
In some cases, your immune system can have a very long memory.
“Some natural diseases can give you lifelong immunity,” Jameson says. “You only get it once and you are protected for the rest of your life. “
Vaccines mimic natural disease to stimulate an immune response. But vaccines may need to be increased to keep that immunity strong. The B-memory cells targeting the COVID-19-induced coronavirus may not have the staying power of the cells that protect us from measles, for example. So far, scientists have claimed that these B memory cells persisted for several months after a case of COVID-19, but it is too early to say anything about whether they will extinct.
“The good thing is that there would be a chance if it turned out that some of the immune response was declining,” Jameson says. “Then, like many other vaccines, maybe … you get another increase after a year or something. “
These questions reflect what scientists have come to understand about our immune system in recent years. COVID-19 also clarifies what we do not yet know about how the immune system protects us from infectious bacteria.
“It’s been really interesting to see this unopened in real time,” Pepper says, “because we’re learning so much about this virus and the immune response to it, in a way that didn’t we have never been before. “
You can contact NPR science journalist Richard Harris at [email protected].
