Zika vaccine has positive results in mice

A vaccine against the Zika virus has tested positive in mice. The immunizer had the ability to limit viral replication in both adult females that were not pregnant and those that were — in this case, also protecting the fetus.

The research results were published in an article in Microbiology Spectrum, a journal linked to the American Society for Microbiology.

To date, there is no vaccine against Zika, a virus transmitted mainly by the bite of the Aedes aegypti.

Another form of infection is from mother to fetus. It is in these situations that the so-called congenital zika syndrome (CZS) can occur, a set of sequelae caused by infection during pregnancy, such as microcephaly.

“The biggest problem we have with Zika is how harmful it is to a fetus,” says Patrícia Braga, a professor at USP’s ICB (Institute of Biomedical Sciences) who is researching Zika. She did not participate in the study.

In Brazil, the cases of zika registered in 2022 have already surpassed those of recent years. According to the most recent epidemiological bulletin from the Ministry of Health, as of August 13, 9,916 probable cases have been registered across the country. Compared to 2019, before the pandemic, the number represents an increase of 21%. In relation to 2021, the records almost doubled.

The immunizer is the result of genetic modifications of Zika so that it has no capacity for viral replication.

As a result, this modified virus infects only a limited number of cells, which induce the body’s immune response without disease progression.

With the vaccine model developed, the researchers tested the safety of the drug in animals. For this, newborn mice were divided into two groups: one of them was infected with the Zika virus and the other had the vaccine injected. After five days, it was observed that all those in the Zika group had died and had a viral load in their blood. On the other hand, the vaccinated animals remained alive and without the presence of the virus in the blood.

In addition to safety, the study also observed the results of the immunizer in preventing complications caused by the disease. In this case, adult mice were vaccinated and compared with another group that received a placebo. So they were both exposed to the Zika virus. In relation to the immunized, there were no complications or weight loss. In addition, viral replication was contained within three days.

The situation was the opposite in the placebo group of mice: they lost weight and 37% showed signs of limb paralysis.

The research also measured the effects of the immunizer in pregnant mice. Safety and effectiveness in preventing complications were also seen in these vaccinated animals compared to those that were not immunized.

In addition, the researchers analyzed the fetuses to determine whether there were malformations associated with the infection. In the case of pregnant mice that were vaccinated, the fetuses had no problems after infection. However, in the control group, many of them experienced weight loss or even decomposed in the womb.

Defense mechanism and memory

The immune system uses different means to protect the body in case of infections. One of these better known forms is antibodies. Another model is through T lymphocytes.

In the case of the Zika vaccine, the researchers came to the conclusion that the main defense mechanism induced by the drug was lymphocytes.

“These cells are able to respond quickly if a Zika infection occurs,” says Braga.

The professor explains that lymphocytes recognize cells infected by pathogens and destroy them in order to prevent viral replication and thus contain the evolution of the disease.

In addition to the defense mechanism, the researchers also looked at the memory of the immune system. “The vaccine was able to induce a cellular response against the virus and a memory response. In other words, when it comes into contact with the virus again, there will be a rapid response against it”, says Braga.

The promising results, however, have yet to be tested in humans. Animal tests, such as the one reported in the new article, are intended to measure the safety of new drugs. Only with human trials, mainly in phases 2 and 3, will it be possible to conclude how effective the vaccine is.