Vaccines may do more than protect people from the immediate effects of a viral infection. New research suggests they could also help prevent lasting damage to the immune system that remains even after the virus has disappeared.
Scientists at Pompeu Fabra University discovered that mice recovering from an acute viral infection experienced prolonged problems with their immune defenses. Although the animals had successfully fought off the virus, their immune systems remained impaired, making it harder to respond to new threats. Remarkably, mice vaccinated before infection did not develop these problems, suggesting that vaccination may provide an additional layer of protection beyond preventing illness.
Most people think of common viral infections, such as colds or stomach viruses, as temporary illnesses. A virus enters the body, multiplies, causes symptoms, and is eventually brought under control by the immune system. Once symptoms disappear, recovery is generally considered complete. The immune response also creates protection against future encounters with the same virus.
But what if the immune system continues to experience harmful effects long after the infection appears to be over?
Viral Infections Can Leave Lasting Immune Damage
Researchers from Pompeu Fabra University’s Infection Biology Laboratory investigated this possibility in a study published in Cell Death & Disease.
Using mice with acute viral infections, the team examined what happened to their immune systems after the animals had recovered. They found that eliminating the virus did not necessarily restore normal immune function. Instead, the infection left behind changes that persisted well beyond the initial illness.
According to Andreas Meyerhans, an ICREA research professor at UPF, who led the research, “there is a general perception that an acute viral infection is a relatively minor and transient event: once the virus is controlled and the symptoms have resolved, the body has fully recovered and is back to normal. But this view may underestimate consequences that are not immediately visible and can persist long after the infection itself has resolved.”
The researchers traced these lingering effects to significant changes in the spleen, an organ that plays an important role in coordinating immune defenses. As the immune system fought to eliminate the virus, the spleen developed fibrosis, a condition involving the buildup of scar-like tissue. The arrangement and positioning of immune cells within the organ also became disrupted.
These structural changes interfered with the interactions between immune cells that are necessary to activate T cells. These specialized cells are essential to adaptive immunity because they help recognize and destroy infected cells.
As a result, the mice remained less capable of launching effective immune responses when exposed to new challenges. Even though the original infection had been brought under control, their immune defenses continued to function poorly.
“The infection can be controlled, but that does not necessarily mean that the host has fully recovered,” says Dr. Paula Cebollada Rica, first author of the study. “Our findings show that the immune-related consequences of an acute viral infection can persist beyond the period in which the virus is detectable, leaving the animals in an immunocompromised state.”
Vaccination Prevented Lasting Immune System Damage
After identifying these long-term effects, the scientists investigated whether they could be avoided. They focused on vaccination, which prepares the immune system to recognize and fight a pathogen before an infection occurs.
The results revealed a striking difference between vaccinated and unvaccinated animals. Mice that received vaccination before infection did not develop the spleen damage or immune dysfunction seen in the other group.
Their spleens maintained their normal structure, and their T cells continued to function at levels comparable to those of mice that had never been infected.
This finding suggests that vaccination can protect the immune system itself from some of the harmful consequences of fighting a viral infection. In the mouse model, vaccination not only protected against the disease caused by the virus but also preserved the animals’ ability to respond to future immune challenges.
“Vaccinated animals did not experience T-cell dysfunction or splenic alterations after recovering from an acute viral infection. This means that vaccination not only prevented the disease resulting from the acute infection but also preserved the immune system’s ability to cope with new challenges,” Cebollada Rica explains.
A Hidden Benefit of Vaccines With Public Health Implications
The findings broaden the potential benefits of vaccination by highlighting a form of protection that may not be immediately apparent. Beyond reducing the immediate effects of an infection, vaccines may also help prevent persistent changes that weaken immune defenses.
Although these results were obtained in mice and do not establish that the same effects occur in humans, they raise important questions about how viral infections influence long-term immune health and how vaccination might help protect it.
The research also comes at a time when vaccination policies and infectious disease prevention efforts are increasingly influenced by political decisions. The researchers emphasize the importance of scientific evidence in understanding the full consequences of infections, particularly when policy choices can undermine coordinated efforts to prevent infectious diseases.
Understanding the broader benefits of vaccination could therefore influence not only medical care but also how public health officials explain the value of vaccines to the public.
“The benefits of vaccination highlighted by this research are important not only for healthcare, but also for how we communicate the value of vaccination to the population at large,” Meyerhans states. “It is important that people are aware of the broader protection that vaccination can provide and continue to trust in vaccines as one of the most effective tools to prevent diseases. Put simply, vaccines provide strong health benefits at a relatively low cost to society.”