Animal study suggests vaccines block in-utero Zika transmission

Mouse mom
Mouse mom

anyaivanova/ iStock

Researchers today reported the first animal trial results suggesting that Zika vaccines may prevent females immunized before pregnancy from passing the virus to their offspring.

In other Zika developments, a human rights group said yesterday that the Zika outbreak in Brazil revealed sanitation and public health gaps that pose threats to residents, especially women, and India's government announced a plan to start screening infants for Zika-related microcephaly.

Two vaccines show promise in mouse experiments

For the study, a team from the National Institute of Allergy and Infectious Diseases (NIAID) and their partners at the Washington University School of Medicine and the University of Texas Medical Branch tested two experimental Zika vaccines, immunizing female mice before breeding them, then testing for the virus in the resulting fetuses. Their results appear today in the early online edition of Cell.

A vaccine that can offer sterilizing immunity—preventing all Zika infection—is crucial for preventing viremia in mothers and resulting birth defects in babies. The US government is supporting the development of several candidate Zika vaccines to improve the chances of having one available by 2018 to protect at-risk populations. In developing a Zika vaccine, researchers are faced with the need for one that can provide fast and durable immunity with a good safety profile—with as few doses as possible to help streamline vaccination campaigns, especially in developing countries.

The two experimental vaccines assessed were a live-attenuated vaccine developed by UTMB and a novel messenger RNA (mRNA) vaccine developed by Moderna. One group of nonpregnant female mice received two doses of mRNA vaccine 28 days apart, with a control group receiving two doses of placebo on the same schedule. Another group got a single dose of live-attenuated vaccine, while a control group received a single dose of placebo.

Both of the vaccines prompted high levels of neutralizing antibodies against Zika virus in the female mice.

Next, researchers mated the female mice and infected them with Zika virus. A week after their mothers were infected, most fetuses showed no evidence of Zika infection. Compared to pregnant mice that received placebo, the vaccinated pregnant mice had markedly lower amounts of Zika RNA in maternal, placental, and fetal tissues, suggesting that the vaccines protected against placental damage and fetal demise.

The findings suggest that both of the vaccines can curb transmission of Zika virus from mothers to developing fetuses, at least in mice. The team said further tests on the vaccines are needed and that having a vaccine to prevent Zika-related birth defects is a critical public health need.

Moderna's mRNA vaccine in January entered a phase 1 clinical trial and is supported by a $54.2 million grant from the US Department of Health and Human Services' Biomedical Advanced Research and Development Authority (BARDA). This spring, study findings on a mouse trial of UTMB's live-attenuated vaccine suggested that a single dose provided complete protection against Zika.

Rights group: Conditions keep Brazil vulnerable to Zika

Brazil's neglected water and sanitation systems and other problems such as lack of information about reproductive health leave the population vulnerable to Zika and other mosquito-borne diseases, Human Rights Watch, an international nongovernmental organization, said yesterday in a 103-page report.

Years of neglect, exacerbated by a recent economic recession, have contributed to water and wastewater conditions that allow Aedes mosquito populations to flourish, the report says. The group interviewed people in two Brazilian states hardest hit by Zika virus and also talked to service providers, other experts, and government officials. They also examined government and other data on health surveillance, water issues, and budgets.

Brazilian officials have urged household efforts to empty water storage containers and to eliminate standing water, but Human Rights Watch says one-third of Brazil's population lacks access to continuous water, leaving people with no choice but to fill tanks, which unintentionally become breeding sites for mosquitoes. The report also notes that poor wastewater infrastructure creates standing water, and the group estimates that 35 million Brazilians lack facilities and services to dispose of human waste.

Interviews revealed that some girls and women don't have access to reproductive health services, and many pregnant women said public health workers did not tell them that Zika can transmit through sexual activity, partly because of inconsistent or conflicting information from authorities.

Amanda Klasing, the group's senior women's rights researcher and report coauthor, said in a press release yesterday that Brazilians may see the health ministry's May 2017 declaration of an end to the Zika emergency as a victory, but significant risks remain. "Brazilians' basic rights are at risk if the government doesn’t reduce mosquito infestation over the long term, secure access to reproductive rights, and support families raising children affected by Zika," she said.

India to screen infants for Zika defects

In other international Zika developments, India's health ministry has announced it will screen newborns for Zika-related microcephaly, the India-based Tribune News Services reported today. In May, the World Health Organization (WHO) announced the first local Zika cases in India, all in Gujarat state in the west. Earlier this week, the Indian media said a case was also detected in Tamil Nadu in the south.

The screening will take place at 55 government hospitals across the country and will include head measurements as well as blood tests. A health ministry official said the screening will be done as part of surveillance for other birth defects, and the Zika-specific component will start soon and be done on an experimental basis. He added that microcephaly can result from many different viruses and that so far India hasn't detected any Zika-linked microcephaly cases.

See also:

Jul 13 NIH press release

Jul 13 Cell abstract

Jul 12 Human Rights Watch press release

Jul 13 Tribune story

This week's top reads