A doctor vaccinates an infant against respiratory syncytial virus (RSV) in a treatment room of her paediatric practice.
Swen Pförtner | Picture Alliance | Getty Images
The Centers for Disease Control and Prevention (CDC) have made a significant recommendation concerning Pfizer’s maternal vaccine for respiratory syncytial virus (RSV). This recommendation paves the way for the vaccine to be available in the United States this fall. The CDC advises expectant mothers in their 32nd to 36th week of pregnancy to receive the vaccine between September and January to protect their children from RSV. RSV is the leading cause of hospitalization among babies in the U.S. After an independent panel of advisors voted 11 to 1 in favor of the recommendation, CDC Director Mandy Cohen promptly approved it.
Cohen states, “This is another new tool we can use this fall and winter to help protect lives.” She encourages parents to consult their doctors about the best approach to safeguard their children against serious RSV illness. Either the vaccine can be administered during pregnancy, or an RSV immunization can be given to the baby after birth.
Pfizer’s vaccine, Abrysvo, has already been approved for adults aged 60 and up in the U.S. The CDC’s recommendation arises as RSV and other respiratory viruses, like Covid, exhibit higher levels of transmission in the country. Public health officials hope that Pfizer’s vaccine, as well as other treatments, will better equip the nation to combat RSV in the approaching fall and winter after facing an unusually severe season of the virus last year.
While RSV typically causes mild symptoms similar to a cold, younger children and older adults are especially vulnerable to more severe infections. According to the CDC, the virus claims the lives of hundreds of children under the age of 5 and results in 6,000 to 10,000 senior deaths annually. It also causes 58,000 to 80,000 hospitalizations among children under the age of 5 each year.
Pfizer estimates that its maternal vaccine could prevent up to 16,000 hospitalizations and over 300,000 doctor visits related to RSV if it becomes available in the U.S. this fall and winter. Dr. Luis Jodar, Pfizer’s chief medical officer for vaccines medical development, remarks, “This fall marks the start of the annual respiratory infection season in the Northern Hemisphere, and we are prepared with vaccines against multiple infectious diseases and – for the first time in history – an available RSV vaccine to help prevent disease in two at-risk populations.”
Pfizer’s single-dose vaccine stands as the first RSV treatment to utilize maternal immunization. When expectant mothers are vaccinated, the shot stimulates antibodies that are transferred to the fetus, offering protection against the virus from birth through the first six months of life. The FDA established the 32 to 36-week dosing timeframe upon approving the shot.
In addition to Pfizer’s vaccine, the FDA and CDC granted clearance for an RSV antibody injection for infants manufactured by Sanofi and AstraZeneca. However, this treatment is directly administered to babies. The CDC recommends the injection, called Beyfortus, for all babies under 8 months old and some older infants.
A subgroup of the CDC advisory panel expressed strong sentiments that most infants would not require both Beyfortus and Pfizer’s Abrysvo. Dr. Jefferson Jones, a CDC medical officer, stated during the advisory meeting that the subgroup reviews data to develop recommendation options for the panel.
“The pregnant person and their prenatal care provider will need to make the decision during pregnancy regarding which RSV prevention product to use,” says Jones.
Assessing Abrysvo’s Efficacy and Safety Data
The CDC panel’s recommendation for Pfizer’s maternal vaccine is based on data obtained from a phase three trial involving nearly 7,400 participants. However, in the trial, mothers received the shot between 24 and 36 weeks into their pregnancy, a wider period than the approved dosing timeframe.
The shot demonstrated nearly 82% efficacy in preventing severe RSV disease in newborns and 57% efficacy in avoiding doctor visits due to RSV-related breathing issues within the first 90 days after birth.
Over time, the efficacy slightly diminished. By the six-month mark, Pfizer’s shot was approximately 70% effective in preventing severe disease and 51% effective in avoiding doctor visits.
The FDA advisory panel generally praised the efficacy of Pfizer’s maternal vaccine. However, concerns regarding potential safety risks were also voiced. The trial revealed that a slightly higher number of premature births occurred among mothers who received the shot compared to those who received a placebo: 5.7% versus 4.7%, respectively.
Although Pfizer, the FDA, and CDC staff argue that the difference is statistically insignificant, the FDA’s approval includes a warning against administering the shot before 32 weeks of pregnancy due to the numerical imbalance in premature births. Pfizer will conduct a post-marketing study to examine the risk of premature births associated with the vaccine. Additionally, the study will assess any pregnancy-related complications following vaccination, including eclampsia.
Pfizer plans to launch a pregnancy registry to monitor adverse events that occur after patients receive the vaccine, allowing women and obstetricians to report any issues.
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