We finally have a vaccine against this deadly virus

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The first respiratory syncytial virus (RSV) vaccine was approved by the US Food and Drug Administration. The vaccine, called Arexvy, is given to people aged 60 and over.

The European Medicines Agency recommends the use of this vaccine. A final decision is expected to be made in July 2023. The British Medicines Agency is also examining the evidence.

RSV is quite closely related to the measles and mumps viruses, but unlike those two, it usually causes symptoms similar to those of a common cold.

Transmission occurs through coughing and sneezing and can remain on surfaces for several hours. It is found all over the world, with most cases occurring in winter.

Healthy adults usually have relatively mild symptoms, but RSV infection can be very serious in young children and the elderly.

Babies and young children can be so impaired in their breathing that they require oxygen treatment in the hospital.

It is estimated that RSV causes one in 50 deaths in children under the age of five worldwide.

RSV is more difficult to diagnose in older adults but can be more common than influenza.

It can progress to conditions like pneumonia, which can be fatal. At least 300,000 people worldwide over the age of 65 are hospitalized with RSV infection each year, and about 4% of them die.

A long way

Scientists began work on an RSV vaccine in the 1960s. The first attempt was based on collecting all of the lab-grown virus and chemically preserving it so that it looked like the RSV virus in the human body.

This is a standard vaccine manufacturing technique, but unfortunately it triggered an unexpected immune response.

Vaccinated children responded poorly when they later became naturally infected with RSV. Many ended up in hospital and two sadly died.

The researchers then tried using vaccines against individual parts of the virus and different formulations, but nothing seemed to work.

Eventually, an important part of the virus called the F protein was identified as a likely vaccine target.

However, getting it to work still proved difficult until scientists realized that the protein changed shape once the virus hit the cells in the lungs.

So the trick was to stabilize the F protein in the vaccine so that it stayed the same once it entered the patient’s body.

Developed by British pharmaceutical company GlaxoSmithKline, the Arexvy vaccine is known as a “protein subunit vaccine”.

It contains an artificial version of the correct format of the F protein (called RSV PreF3) as well as a harmless chemical that encourages the body to absorb the vaccine more easily (called an adjuvant).

Eighty-three percent effective

In a clinical trial involving nearly 25,000 volunteers, half received Arexvy and half a placebo, and all were followed up for at least six months. The vaccine provided 83% protection against lower respiratory tract disease caused by RSV.

There are two forms of RSV, types A and B. The vaccine worked equally well against both types.

While some people did experience side effects, these were rare and usually minor. Other, smaller studies of Arexvy have found serious results.

In one study, two people who were given the flu vaccine along with Arexvy developed brain inflammation.

In another study, a person developed a condition called Guillain-BarrĂ© Syndrome, a rare condition in which the body’s immune system turns against itself, causing paralysis.

Most people recover from Guillain-Barré Syndrome, but it can take time.

Experiments are still being carried out to see how long the vaccine’s effect lasts. This type of vaccination usually requires people to have regular booster shots, so it’s likely to be given annually.

Although RSV affects more children than adults each year, there is still no suitable vaccine for children. Because virologists still don’t fully understand how children’s immune systems interact with the virus.

In the meantime, children at high risk of developing serious RSV disease (premature babies and children with certain heart conditions) can be given palivizumab.

This is not a vaccine, but a laboratory-made copy of an antibody against the F protein. It is a safe drug, but the protection does not last long and the injection must be given once a month during RSV season.

Written by Sarah Pitt. The conversation.

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