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Vaccinating pregnant women protects infants against severe RSV infection


 

An investigational vaccine against respiratory syncytial virus (RSV) in pregnant women has been shown to help protect infants against severe disease, according to the vaccine’s manufacturer.

Pfizer recently announced that in the course of a randomized, double-blind, placebo-controlled phase 3 study, the vaccine RSVpreF had an almost 82% efficacy against severe RSV infection in infants from birth through the first 90 days of life, according to a company press release.

The vaccine also had a 69% efficacy against severe disease through the first 6 months of life. A total of 7,400 women had received a single dose of 120 mcg RSVpreF in the late second or third trimester of their pregnancy. There were no signs of safety issues for the mothers or infants.

Due to the good results, the enrollment in the study was halted on the recommendation of the study’s Data Monitoring Committee after achieving a primary endpoint. The company plans to apply for marketing authorization to the U.S. Food and Drug Administration by the end of 2022 and to other regulatory agencies in 2023.

“The directness of the strategy, to vaccinate expectant mothers during pregnancy so that their newborn is then later protected, is new and a very interesting approach,” commented Prof. Ortwin Adams, MD, head of virologic diagnostics at the Institute for Virology of the University Hospital of Düsseldorf (Germany) to the Science Media Centre (SMC).

In terms of the RSV vaccination strategy presented, “the unborn child has taken center stage from the outset.” Because the vaccination route is the placental transfer of antibodies from mother to child (“passive immunity”), “... the medical points of contact for this vaccination will be the gynecologists, not the pediatricians,” Dr. Adams said.

“This concept imitates the natural process, since the mother normally passes immune defenses she acquired through infections to the child via the umbilical cord and her breast milk before and after birth. This procedure is long-proven and practiced worldwide, especially in nonindustrialized countries, for a variety of diseases, including tetanus, whooping cough (pertussis), and viral flu (influenza),” explained Markus Rose, MD, PhD, head of Pediatric Pulmonology at the Olgahospital, Stuttgart, Germany.

The development of an RSV vaccine had ground to a halt for many decades: A tragedy in the 1960s set the whole field of research back. Using the model of the first polio vaccine, scientists had manufactured an experimental vaccine with inactivated viruses. However, tests showed that the vaccine did not protect the children vaccinated, but it actually infected them with RSV, they then fell ill, and two children died. Today, potential RSV vaccines are first tested on adults and not on children.

Few treatment options

RSV causes seasonal epidemics, can lead to bronchiolitis and pneumonia in infants, and is one of the main causes of hospital stays in young children. Monoclonal antibodies are currently the only preventive option, since there is still no vaccine. Usually, 60%-70% of infants and nearly all children younger than 2 years are infected with RSV, but the virus can also trigger pneumonia in adults.

“RSV infections constitute a major public health challenge: It is the most dangerous respiratory virus for young infants, it is also a threat to the chronically ill and immunocompromised of all ages, and [it] is the second most common cause of death worldwide (after malaria) in young children,” stated Dr. Rose.

Recently, pandemic-related measures (face masks, more intense disinfection) meant that the “normal” RSV infections in healthy adults, which usually progress like a mild cold, were prevented, and mothers were unable to pass on as much RSV immune defense to their children. “This was presumably responsible in part for the massive wave of RSV infections in fall and winter of 2021/22,” explained Dr. Rose.

Thomas Mertens, MD, PhD, chair of the Standing Committee on Vaccination at the Robert Koch Institute (STIKO) and former director of the Institute for Virology at Ulm University Hospital, Germany, also noted: “It would be an important and potentially achievable goal to significantly reduce the incidence rate of hospitalizations. In this respect, RSV poses a significant problem for young children, their parents, and the burden on pediatric clinics.”

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