According to foreign media news, the US FDA requires respiratory syncytial virus (RSV) vaccines produced by Pfizer and GlaxoSmithKline (GSK) to add warnings about the risk of Guillain-Barré syndrome (GBS) on the label.

Guillain-Barré syndrome is a rare neurological disease whose cause may be related to infection and immune response. The characteristic symptoms are symmetrical limb weakness, limb numbness, and loss of sensation like wearing gloves and socks, and may cause paralysis.

There are currently three RSV vaccines on the market worldwide, namely the recombinant proteins Arexvy (GSK) and Abrysvo (Pfizer), and Moderna's mRNA vaccine mResvia. The FDA's regulations involve the first two. The

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RSV belongs to the genus Pneumovirus of the family Paramyxoviridae. It is a single-stranded RNA virus that was first isolated from the respiratory tract of chimpanzees in 1956. According to WHO statistics, about 64 million people are infected with RSV each year, and nearly 500,000 adults in high-income countries are hospitalized each year. Vaccination is an effective means of preventing RSV infection, but due to the particularity of the surface protein structure of the RSV virus, RSV vaccine research and development has failed frequently over the past 60 years.

It was not until May 2023 that the FDA approved GSK's RSV vaccine Arexvy for the prevention of lower respiratory tract diseases (RSV-LRTD) caused by RSV in people aged 60 and above, becoming the first FDA-approved RSV vaccine.

In the same month, the FDA approved the second RSV vaccine, Pfizer's Abrysvo, both of which are recombinant protein routes and are suitable for the same population.

Arexvy performed very well after its launch, achieving sales of 1.238 billion pounds (about 1.56 billion US dollars) in 2023. Pfizer's Abrysvo also performed well, selling $890 million in 2023.

However, both vaccines performed poorly in 2024. GSK's financial report shows that Arexvy's sales in the third quarter of 2024 fell 74% year-on-year to 188 million pounds (about 244 million US dollars). Pfizer's Abrysvo also saw sales fall 5% year-on-year to $356 million in the third quarter of 2024.

In May 2024, Moderna's mRNA vaccine mResvia was approved by the FDA to protect adults aged 60 and over from lower respiratory tract diseases caused by RSV infection, becoming the third RSV vaccine to be marketed worldwide. However, the launch of the vaccine did not reverse the downward trend in RSV vaccine sales, with sales of only $10 million in 2024Q3, lower than expected.

The decline in

RSV vaccine sales may be related to its safety.

In June 2024, the Advisory Committee on Immunization Practices (ACIP), an independent vaccine consultant to the U.S. Centers for Disease Control and Prevention (CDC), recommended that RSV vaccines be used only in adults aged 75 and over, while vaccination is no longer recommended for people aged 60-74 who do not have RSV risk factors. After the CDC recommended narrowing the coverage of RSV vaccines for adults, the sales potential of RSV vaccines dropped significantly.

In December 2024, the FDA announced that all RSV vaccine studies for infants and young children were suspended, including studies of Moderna's two vaccines, mRNA-1345 and mRNA-1365, and planned to hold an advisory committee meeting on the 12th to discuss the safety of the vaccine.

In January 2025, the FDA required Pfizer and GSK's RSV vaccines to add warnings about the risk of Guillain-Barré syndrome (GBS) to the labels.

This regulation is based on a post-marketing observation study by the FDA. The FDA used medical insurance claims data to analyze and found that the risk of Guillain-Barré syndrome increased within 42 days after RSV vaccination. Specifically, among people aged 65 and above, there were 9 cases of Guillain-Barré syndrome for every 1 million doses of Pfizer's Abrysvo vaccine and 7 cases for every 1 million doses of GSK's Arexvy vaccine. The FDA believes that the overall evidence shows that Abrysvo and Arexvy are associated with an increased risk of Guillain-Barré syndrome, but the existing evidence is insufficient to determine a causal relationship.

It is worth noting that this is not the first time that the FDA has issued a warning about reports of Guillain-Barré syndrome in vaccinated people. In 2021, federal regulators revised the fact sheet for Johnson & Johnson's (JNJ.US) COVID-19 vaccine, warning that the disease "may present a small risk."

Conclusion: Although the FDA requires an increase in risk warnings for RSV vaccines, it still believes that the benefits of vaccination with Abrysvo and Arexvy outweigh their risks. FDA data show that for every 1 million doses of RSV vaccine, nearly 10,000 hospitalizations in adults aged 60 and above can be prevented.

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