Beyfortus: the RSV shot

I have received many requests to talk about Beyfortus, which is the new monoclonal antibody against RSV that has just been approved by the FDA.

There’s already a lot of confusion about Beyfortus - and a lot of fear-mongering as well.

So lets sort out fact from misinformation.

First, its not a vaccine!

Beyfortus (nirsevimab-alip) is a new option that provides protection against RSV for babies. It is injectable, but there is confusion because of the other RSV vaccines now recommended for pregnancy and in the elderly.

So one more time, let me clarify:  Beyfortus is not a vaccine. It is a monoclonal antibody. Think of it as a medication that is delivered via a shot.

What is RSV?

RSV is a viral infection that causes respiratory infection. For older children, it often presents as a cold or cough. But for younger infants, who have less reserve and smaller airways, RSV infection can be very serious. About 1-3% of children under 1y are hospitalized due to RSV every year.

Here are more details.

What is a monoclonal antibody?

A monoclonal antibody is a medication that contains antibodies that look like the antibodies our own bodies make when encountering an infection (or immunization).

The Pediatrician Mom Summary: Basically, instead of forcing the body to make its own army to fight RSV (which relies on being exposed), you are providing the soldiers so that they’re there and ready to work if RSV does make an appearance.

Protecting your baby from RSV

There are two options now available to help protect babies from RSV. Both provide passive antibody protection.

Abrysvo

This is an RSV vaccine available in the third trimester of pregnancy Note: also available for adults over 65y but I’m focusing on pediatrics here.

• Given between 32 - 36 weeks gestation during the RSV season

• Idea is to provide passive immunization via transfer of antibodies across placenta.

• When compared to placebo, found to be effective at preventing RSV infection in infants by up to 82% in the first 90 days and 70% in the first 6 months of life

• No concerning safety signals. Side effects are what you’d expect: site reactions, headache, body aches, etc. Question of slightly increased risk for preterm delivery if given before 32 weeks (which is why it is given btwn 32 - 36 wks ).

Sources: FDA, ACIP meeting data, Pfizer Report Study c3671008, PMID: 37018474, ACOG

Beyfortus

This is an RSV monoclonal antibody given to babies via injection.

• Given during RSV season (October to March) to eligible babies:

  • Infants between 0 - 8 mo during their first RSV season (October - March) whose mothers did not get Abrysvo >14 days before delivery

  • Babies aged 8 - 19 mo with specific high risk conditions that are entering their second RSV season

• Effective at preventing severe RSV infection by about 77-98% depending on which study you looked at. Safety & effectiveness data are comparable in studies from US, Spain & France!

• Provides some protection within hours of getting the shot

• No safety red flags; there has been a lot of fear-mongering online about the side effects but these are generally rare (and mild) - ranging from fever, injection site reactions and rash.

  • There were some infant fatalities in the trials, but these have been investigated and the cause is thought to be unrelated to the antibody. For example, in this study (PMID 32726528), deaths in the Nirsevimab group were a result of other known infections (such as sepsis or meningitis), and undiagnosed cardiac disease. In this study (PMID: 35235726), infant fatalities were also thought to be due to unrelated infections (GI) or underlying chronic conditions.

• Getting both Abrysvo & Beyfortus is not recommended except in very specific circumstances (see CDC)

• Keep in mind that Beyfortus is PREVENTIVE. It is not an RSV treatment. It decreases the severity of illness, so you need to have it on board before exposure.

• Remember: Beyfortus shouldn’t be given to those with a history of serious allergic reactions, or those with concerns of “clinically significant bleeding disorders”. As always, talk to your doctor if you are concerned.

Source: ACIP meeting data, CDC

Synagis:

Most parents dont know that we have been using a different monoclonal antibody for RSV prevention in the highest risk babies for years.

Synagis (Palivizumab) is an RSV-specific monoclonal antibody which is extremely expensive. Pediatricians historically spent a lot of time arguing with insurance companies about approval because of the cost.

The game-changing difference between Synagis and Beyfortus is the duration of effect.

Synagis needed to be given every month during RSV season because its effect doesn’t last as long in the body. Beyfortus offers several months of protection from a single dose.

If choosing between Abrysvo & Beyfortus, is one better than the other?

Both are great options! Last year there were supply and access issues around Beyfortus but I think that will be improved this year — however, not every pediatrician seems to be offering it. So I would go with whichever is accessible and reliable to get.

For pediatricians, RSV is a scary disease because of how quickly infants who have it can deteriorate. There is also some data suggesting that severe RSV infection in infancy may increase risk for long-term health conditions like asthma.

Most pediatricians (myself included) see Beyfortus as a game-changing intervention.