(CNN) A recent batch of studies, many early stage and not yet peer reviewed, show that humans have a "robust" immune response to Covid-19 that may protect them from further infection, even if they had mild symptoms. How long that protection lasts is still unclear, but the studies indicate it could last for months.
One leading immunologist says the findings provide optimism that people will not have to endure repeated coronavirus infections. It also provides evidence a vaccine might protect people for more than a short time.
"The hopes that I've had appear to be realized with these early studies," said Dr. Ian Lipkin, director of the Center for Infection and Immunity at Columbia University Mailman School of Public Health.
Early in the pandemic, some scientists questioned how long the body would remember the infection and continue to produce antibodies -- the proteins the body makes to fight an infection -- to protect it. Studies showed these antibodies decline over time and different people produce different numbers of antibodies. It's been unclear what kind and what level of an antibody response is needed to provide protection.
"This is an accumulation of more information that allows people to become more comfortable with the idea that we are going to have immunity that's going to be longer in duration," Lipkin told CNN. "We don't know that for a fact, but there are a few things that are interesting that gave me a basis for optimism."
One of the studies showed that T cells appear to be activated by this novel coronavirus. T cells are important immune cells that stimulate various arms of the immune system and that also attack and kill cells already infected by a virus.
Another study that looked at donor blood samples found that a big part of the population, between 20% to 50% of people in some areas of the US, may have T cells that recognize the novel coronavirus, even if that person has never been infected. It's still unclear why people have them. It may be what's called cross-protection from other coronaviruses that cause the common cold. What scientists still don't know is if this provides protection against Covid-19, but it has potential.
"So, this is very good news and it's optimistic," Lipkin said. "You know, it is a bit of blue sky that we've been looking for."
Jennifer Gommerman, who worked on one of the early studies, found that the antibody response to this novel coronavirus is "actually quite durable."
"The immune response is doing exactly what we would expect it to," Gommerman, an immunologist at the University of Toronto, told CNN. "At least at about four months, which is, as far as, most of us can measure at this point in the pandemic," Gommerman said.
Gommerman said there is some decay in the level of antibodies, as one would expect in a normal immune response, but it does not plummet.
Gommerman said another study coming out from immunologist Marion Pepper's work at the University of Washington finds that the immune response is not a "one-trick pony." Instead it is like a "Swiss Army knife that has a lot of different tools" for fighting the novel coronavirus.
Pepper's study shows that some of the T cells form memory T cells that can hang around and help provide protection in case a person encounters the novel coronavirus again. From studies that look at SARS, another coronavirus, research shows that the memory T cell response is long lived.
Gommerman said since scientists have not seen a record of re-infection, even with as widespread as the pandemic is, that strongly suggests the body's immune system is working well against this threat, and re-infection is less likely.
"So that is all good news," Gommerman said. "That means that people who are infected with this novel coronavirus should have the capacity to mount what's called a memory immune response to protect themselves against infection."
What remains unclear is how long the human body's response to the novel coronavirus can provide protection. Since it's only seven months into the pandemic, these studies cannot determine how long protection lasts, but at least one shows even having a mild infection provided three months of protection and suggests that protection will likely last longer.
"The hard part about durability is that's a time dependent measurement," said David Masopust, a Howard Hughes Medical Institute scholar in the department of Microbiology and Immunology at the University of Minnesota. "We'd really like to know five years from now how that looks. Unfortunately, we can't predict that today," Masopust added. The research results are what scientists would expect from a coronavirus, he said.
"What the research is showing us is encouraging -- that things are looking normal in the sense that you have what we call humoral immunity, or antibodies," Masopust told CNN.
"And you develop B cells, which can differentiate into cells that make antibodies, and it looks like you have T cells that looked durable, to the extent that this study was capable of looking at that," he added. "The bad or sad news would be if they had gotten something different from these studies."
Masopust said while these studies are encouraging, it is still unclear whether the immune system's memory can actually protect people from infection. "Again, that's a real world experiment that, will unfortunately be done by the people come into contact with the coronavirus," Masopust said.
Gommerman said the findings about this robust immunity response mean that any future vaccine should also provide protection for a useful period of time.
"This durable immunity that we are seeing means that when we do come up with a vaccine that is well designed and it's safe, a vaccine can replicate what the virus does," Gommerman said. "People need to take it when it comes along."