With the end of summer fast approaching, we once again face the possibility of a “tripledemic” of Influenza, COVID-19, and Respiratory Syncytial Virus (RSV) during the fall and winter. However, unlike in previous years, we have a rapidly developing arsenal of defenses against RSV for the most vulnerable groups.
RSV is a common respiratory virus that affects people of all ages, but it is particularly dangerous for infants, young children, and older adults. An estimated 58,000-80,000 children under the age of 5 are hospitalized annually due to RSV infection in the United States. RSV also results in 60,000 to 160,000 hospitalizations and 6,000 to 10,000 deaths annually in Americans over 65.
RSV Vaccines for Older Adults
In May 2023, the FDA approved two RSV vaccines for adults 60 years and older. Pfizer’s Abrysvo and GSK’s Arexvy have several similarities in terms of their effectiveness and side effects. In clinical trials, the Pfizer vaccine (Abrysvo) was 89% effective at preventing lower respiratory symptoms associated with RSV in the first RSV season after vaccination. The GSK vaccine (Arexvy) was 83% effective in preventing these symptoms. Both vaccines work in the same way biologically by targeting a protein that the RSV virus uses to fuse to human cells. They were developed based on the same scientific discovery from a decade ago.
The vaccines were somewhat less effective in preventing disease in the second RSV season after people received a shot. However, RSV does not mutate like influenza and SARS-CoV-2, so there shouldn’t be a need to update the vaccine or re-dose people every year. Out of approximately 38,000 people who received either vaccine, 20 experienced atrial fibrillation, and six developed neurological complications such as encephalomyelitis and Guillain-Barré syndrome in the weeks after vaccination. More common side effects included fatigue, fever, and muscle pain at the injection site. In July, the CDC advised that people talk to their doctors when deciding whether to get the shot.
The RSV vaccine appears to have good durability, lasting at least eight months. This makes timing the shot easy because even if someone gets the RSV vaccine now, it will see them through this winter’s RSV season. The RSV vaccine is also safe to receive at the same time as the Influenza vaccine.
Monoclonal antibodies for infants
In July 2023, the FDA approved a monoclonal antibody shot called nirsevimab (developed by Beyfortus, AstraZeneca, and Sanofi) to protect infants and toddlers at high risk for severe RSV disease. Monoclonal antibody therapy is not a vaccine but can provide an infusion of prefabricated antibodies, giving temporary protection for up to five months to newly developing pediatric immune systems. In a clinical trial, the drug was approximately 77 percent effective against both hospitalizations and cases of RSV requiring a doctor’s visit. Side effects were mild, with a rash at the injection site being the most common.
The CDC recommended that infants under 8 months old at the start of RSV season receive nirsevimab. Children between the ages of 8 and 19 months are also recommended to get the shot if they have an increased risk for severe disease. That includes children who are immunocompromised or have pre-existing lung conditions and American Indian and Alaska Native populations. Babies should be able to receive the monoclonal antibody therapy at their pediatrician’s office, and some hospitals may offer the shot to newborns delivered during RSV season.
RSV Vaccines for Pregnant Women
Earlier this week, the FDA approved the first maternal vaccine intended to help protect newborns against RSV, called Abrysvo and developed by Pfizer. The vaccine is given during late pregnancy to reduce newborns’ risk of severe RSV infection. It works by passing antibodies down to infants during pregnancy, providing an immediate but temporary shield. Vaccines for influenza, diphtheria, tetanus, and pertussis are also given as maternal immunizations.
The vaccine was found to be 82 percent effective at protecting infants from severe illness during the three months after birth and waned to 69 percent effective over six months during a double-blind study. The study found no major safety concerns. The FDA reported the most common side effects in trials were pain at the injection site, headache, muscle pain, and nausea.
The FDA also noted a slightly higher percentage of Abrysvo recipients experiencing preterm births (5.7 percent) compared with placebo recipients (4.7 percent). It was unclear whether the vaccine caused the imbalance, but providers can avoid the risk of preterm birth by administering the vaccine between weeks 32 and 36 of gestation.
However, the vaccine won’t be available immediately, as it still awaits an evaluation from an expert panel at the CDC and the CDC director’s sign-off. This process could take months. The CDC’s Advisory Committee for Immunization Practices is scheduled to meet from October 25-27, when they could decide on the recommended use of Abrysvo for pregnant women.
A contributing factor to last year’s tripledemic was that a majority of US kids hadn’t received a flu or COVID vaccine. As of December 2022, according to the CDC, nearly 60% of children ages 6 months through 17 years hadn’t received the flu vaccine, and 90% of children ages 6 months through 4 years hadn’t received a Covid-19 vaccine.
Even with these new tools against RSV, public health officials must ensure clear messaging and a smooth, accessible rollout or risk eroding confidence in routine vaccination and overwhelming the health-care system with preventable cases of RSV.