Breakthrough new vaccine protects against Zika virus while preventing serious side effects

Ten years ago, the Zika virus shook Brazil. Thousands of babies were born with severe birth defects. Pregnant women faced constant fear, and public health systems scrambled for answers. While the headlines faded, Zika never truly disappeared. The virus still lingers, and so does the risk.

But now, a major step forward has been taken. Scientists at the University of São Paulo’s Medical School, at the Institute of Tropical Medicine, have developed a vaccine that protects against the Zika virus—and it has passed a key safety and effectiveness test in mice.

The results, published in NPJ Vaccines, showed that the vaccine does more than stop infection. It also guards against brain swelling and damage to the testicles—two serious effects of the virus in laboratory studies. Although testicular damage hasn’t yet been widely seen in human cases, it’s a growing concern in the scientific community.

“We were able to design a formulation that can neutralize the pathogen and protect rodents from both brain inflammation, one of the most worrying consequences of infection, and testicular damage,” said Gustavo Cabral de Miranda, the lead researcher on the project.

The research was funded by FAPESP, a public foundation in Brazil that supports science and innovation.

Unlike some older vaccines, which rely on injecting weakened or dead viruses, this new vaccine avoids using any genetic material from the Zika virus. Instead, the team used a modern and safer method: virus-like particles, or VLPs.

These VLPs look like viruses but don’t contain any of the genetic material that allows viruses to multiply. That makes them unable to cause infection, while still triggering a strong response from the immune system. It’s like showing the immune system a mugshot of a criminal instead of letting the criminal loose in the body.

This approach has several advantages. It reduces the risk of side effects, lowers production costs, and removes the need for added substances called adjuvants, which are often used to boost immune responses.

“Unlike more traditional strategies… we don’t use the pathogen’s genetic material, which makes its development much safer and more economical,” Miranda explained.

The vaccine has two key parts. First is the VLP, which acts as a decoy virus to alert the immune system. The second part is the viral antigen, specifically a protein segment from the virus called EDIII. This portion helps the body create specific antibodies to block the virus from attaching to human cells.

The team used a platform known as QβVLP, which has already been tested in other vaccines. This platform was produced in a laboratory using E. coli bacteria and chemically bonded to the EDIII protein. When injected, this combined structure mimics a real virus, helping the body mount a full immune defense.

“When the formulation is injected into the body, this combination activates a strong immune response, including antibodies and Th1 cells,” explained Nelson Côrtes, the first author of the study. Th1 cells are a type of white blood cell that play an important role in fighting infections.

The researchers didn’t stop at checking whether the vaccine blocked infection. They also studied its effects on several organs, especially those known to suffer damage from the Zika virus in animal studies.

Genetically modified mice that are more sensitive to Zika were used for this part of the research. After being vaccinated, these mice produced antibodies that were able to neutralize the virus. The vaccinated animals did not experience brain inflammation or testicular damage—two known dangers of the infection in laboratory models.

The damage to testicles caused by Zika can lead to problems with sperm production and long-term fertility. This hasn’t been confirmed in humans yet, but early lab studies suggest it may be possible. Because Zika can be spread through sex, protecting reproductive organs is critical.

“The vaccine demonstrated the ability to protect male mice against testicular damage,” said Côrtes. “This is important, given the known risks of sexual transmission… and its potential to negatively affect spermatogenesis and reproductive health as a whole.”

The vaccine’s protective effects were also seen in other organs, including the kidneys, liver, and ovaries. While brain and reproductive damage get the most attention, the virus can impact the whole body in various ways. The new vaccine helps defend against these effects.

One of the trickiest challenges in making a Zika vaccine is its similarity to another virus: dengue. Dengue has four serotypes—think of them as cousins of the same virus—and all are common in the same places where Zika spreads.

This closeness confuses the immune system. Antibodies made to fight one virus might partially recognize another. While that might sound like a good thing, it can actually backfire.

If the immune system recognizes a related virus but can’t stop it completely, it might actually help the second virus get into cells more easily. This is called antibody-dependent enhancement (ADE), and it has been seen with dengue infections. In the worst cases, this can lead to more severe illness than the first infection.

Fortunately, the researchers took that into account. The EDIII protein used in the vaccine is very specific to Zika and doesn’t create this kind of cross-reaction.

“The vaccine doesn’t cause a cross-reaction, which is very positive,” said Miranda. “Using the EDIII antigen allows the immune system to produce antibodies that are more specific to the Zika virus.”

This careful design helps avoid the risk of ADE and makes the vaccine safer in regions where both Zika and dengue are present.

Although this study was done in mice, it lays the groundwork for possible human trials in the future. The researchers are optimistic but cautious.

Zika remains a threat, especially in countries where the virus is endemic and mosquito populations are high. Pregnant women are most at risk, as the virus can pass to the unborn child and cause birth defects like microcephaly. But men are also at risk due to the possibility of sexual transmission and long-term effects on fertility.

Vaccine development for viruses like Zika is slow, in part because outbreaks are unpredictable. When infections decrease, fewer people are available for vaccine testing. That’s why laboratory studies like this one are so valuable—they allow scientists to test new ideas even when public attention fades.

This study represents a meaningful step forward. It proves that a virus-like particle vaccine can produce a powerful immune response without using live virus or creating risky side effects. It also shows that protection can extend beyond basic immunity, offering organ-level defense.

While more work is needed, including safety tests in larger animals and, eventually, humans, the early signs are promising. A future where Zika no longer threatens pregnancies, public health, or reproductive health might be closer than many thought.

Note: The article above provided above by The Brighter Side of News.

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