An unusual RSV season ahead for 2023—after nirsevimab but before a vaccine

Experts say that Canadian physicians should be ready for a unique respiratory syncytial virus (RSV) season in 2023; one featuring a new monoclonal antibody for prophylactic treatment but without approval yet for the much anticipated vaccine for people who are pregnant. This coming season, parents and caregivers also know more about RSV given the early and active season in 2022, noted experts in RSV, who shared their views at the Canadian Immunization Conference, held in Ottawa in late April. But what about for adults? Physicians should also watch for the virus in older adults, which presents differently and can lead to further infections or functional decline. Health Canada approved the new monoclonal antibody nirsevimab (Beyfortus) on April 19. It will be available as prophylactic treatment, but Dr. Jesse Papenberg, a pediatric infectious disease specialist at Montreal Children’s Hospital, suspects initial supplies will be low. Nirsevimab was approved to prevent serious illness from RSV. Its efficacy was assessed using pooled results from two large clinical trials featuring a total of 2,350 healthy pre-term and term infants. Infants who received nirsevimab had significantly fewer hospitalizations or cases of severe RSV compared to those who received a placebo. The bulk of the trial data involves healthy infants. “We don’t have actual efficacy data for kids who are high risk,” Dr. Papenburg noted. Currently, the only other prophylactic treatment for infants is palivizumab (Synagis). While palivizumab must be injected four times during RSV season, nirsevimab is given as just one. Nirsevimab may also be less expensive; the exact costs to the province has yet to be determined, but early reports from the United States put the cost at around $300 per dose, less than palivizumab. Provinces and territories have been tightening indications for receiving palivizumab in the past few years, based partly on cost-effectiveness. Research suggests that infants who have established risk factors for severe RSV, those who are usually given palivizumab, actually represent a minority of hospital admissions. The distribution of nirsevimab will probably be tightly regulated by the provinces and territories this season, Dr. Papenberg said. Physicians in the clinic won’t have to decide if an infant gets it or not, the provinces and territories will provide the indications. The National Committee on Immunization isn't expected to release guidelines on nirsevimab use until the vaccine for use in pregnancy is approved, Dr. Papenburg said. Read: Health Canada approves new antibody drug to help prevent serious RSV in babies The search for an RSV vaccine pregnant people has been long, but one may arrive in Canada soon. Pfizer Canada has submitted their vaccine to Health Canada for approval. A phase 3 randomized clinical trial of the vaccine involved 3,682 pregnant people (24 to 36 weeks gestation) who received the vaccine, and 3, 676 who received the placebo. The vaccine was 81.8% effective in preventing severe lower respiratory tract illness that required medical care in infants three months or younger. It was 57.1% effective in preventing RSV-associated illness in infants three months old or younger, but this was not statistically significant. There were no safety concerns. In future years, provinces and territories will have to decide how to prevent RSV in infants. Nirsevimab may prevent more disease, but the vaccine given to pregnant people may be cheaper, Dr. Papenburg said. Uptake to the vaccine may be low, as fewer people who are pregnant get the influenza vaccine or the Tdap vaccine than recommended. The 2022 RSV season was early in many parts of Canada, and there were more cases compared to previous years when restrictions to limit the spread of COVID-19 were in place. This, combined with the shortage of pain-relief medication for children, means that many parents and caregivers are more aware of RSV and its risks, Dr. Papenburg said. If parents ask about nirsevimab as a prophylaxis against severe disease, physicians can tell them that availability is up to the province or territory, he said. Vaccines against RSV for adults are also under development. Moderna Inc. announced in January that their mRNA vaccine targeting RSV was 83.7% effective against RSV-associated lower respiratory tract disease in older adults. GlaxoSmithKline (GSK)’s vaccine (Arexvy) was approved by the U.S. Food and Drug administration in early May. It is based on RSV’s perfusion F protein. Results from its phase 3 clinical trial suggest the vaccine reduced the risk of developing RSV-associated lower respiratory tract disease in older adults by 82.6%. Pfizer Inc.’s perfusion F protein-based vaccine was found to be 66.7% effective in preventing RSV-associated lower respiratory tract illness in older adults when tested in a phase 3 randomized clinical trial. While we often hear about RSV in relation to infants, older adults who contract RSV are at higher risk of other infections, including to pneumococcal disease, said Dr. Melissa Andrew, professor of medicine in the division of geriatrics at Dalhousie University in Halifax. Read: U.S. approves first vaccine for RSV after decades of attempts Dr. Andrew and colleagues published a study in the Journal of the American Geriatric Society in 2020 showing functional decline in seniors following hospital admission for respiratory infections, which includes RSV. They found that 20% of older adults leave hospital with a decreased level of strength. “That can be catastrophic,” she said. How a RSV vaccine for older adults will be funded by provinces and territories is another question. “One might imagine an older age cut-off,” Dr. Andrew said. She said she envisions a suite of RSV vaccines available to older adults given the number in development. For now, Dr. Andrew advised physicians to realize that older people often present atypical symptoms of RSV, such as having a cough and no fever. She said it is important to test older adults for RSV and to observe droplet precautions to limit spread. Treatment is supportive, ensuring patients are hydrated and start moving as soon as possible. Physicians should continue to monitor patients for other infections if they have RSV. Read: Would you recognize measles? Canadian docs need to get reacquainted

An unusual RSV season ahead for 2023—after nirsevimab but before a vaccine

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