UK hospitals are seeing an increase in the number of children suffering from severe respiratory infections. This includes a non-seasonal outbreak of an infection called respiratory syncytial virus (RSV) among children as young as two months of age.
This has led to an increase in hospitalizations for bronchiolitis, an inflammation of the lungs similar to bronchitis.
Why does the peak incidence of RSV, considered a winter disease, occur in the summer of 2021?
Simply put, the restrictions put in place to prevent the spread of COVID-19 have contained the spread of other respiratory viruses as well. As many countries lift these restrictions, many respiratory diseases are spreading again.
RSV is a common respiratory pathogen - so common that almost all of us are infected by it by the age of two. In the vast majority of people, this virus causes a mild illness that resembles a severe cold, with a runny nose and cough. These symptoms usually go away without treatment within a week or two.
However, in about one in three children, RSV can cause bronchiolitis, an inflammation of the bronchioles, the smallest tubes in our lungs. This restricts the airway and patients experience fever and difficulty breathing, often making a wheezing sound when drawing in air.
Although bronchiolitis can often be managed without the aid of fluids and paracetamol, it can sometimes develop into serious illness. If a teenager has severe difficulty breathing, symptoms may worsen, resulting in a fever over 38 degrees Celsius, blue lips, and difficulty breathing.
In young children, this can lead to long-term feeding and dry diapers. This is when many parents make the right decision to take their child to the hospital.
Very young children - babies in the first months of life - are most susceptible to hospitalization due to their smaller airways.
Although most cases can be controlled, bronchiolitis is sometimes fatal. Approximately 3.5 million children worldwide are hospitalized annually, and about 5 percent of these cases, unfortunately, end in death.
It appears that COVID measures such as more frequent hand washing, wearing masks and reducing close contact between people have led to a significant reduction in the influenza season in the winter of 2020-21.
The same is true for RSV: studies have shown that in the northern hemisphere there are 84% fewer hospitalizations due to bronchiolitis than in previous years. A significant decrease was also noted in Australia.
Now the opposite is happening, affecting an entire year of newborns who weren't exposed to high numbers of respiratory viruses while the restrictions were in place.
We do not know why some children infected with RSV have mild symptoms while others become severely ill. Many risk factors have been identified associated with severe RSV disease, including age (most at risk in one-month-old babies), gender (men have a statistically higher risk than women), environmental factors such as exposure to smoke, underlying lung disease, and some genetic factors.
Despite this knowledge, it is still impossible to conclusively determine which children will develop bronchiolitis. However, in some countries, people are considered to be at high risk for these known risk factors and are treated with prophylactic treatment.
As with all infectious agents, a reliable immune response is the key to clearing the infection. We know that a large number of neutralizing antibodies (including maternal antibodies and antibody preparations such as palivizumab) protect against severe illness.
However, immunity to RSV is not complete or particularly long-lasting, as most of us become reinfected during our lifetime. This is one of the reasons why, despite the tremendous efforts of many research groups, there are currently no vaccines.
In addition, our immune system can sometimes wreak havoc on the body in an attempt to clear it of infection. In RSV, certain immune responses have been shown to increase the severity of the disease and are associated with the development of asthma.
Due to the widespread prevalence of RSV and asthma in the UK, the link between the two is being studied extensively, including through the Wellcome Trust funded Breathing Together project, which I am currently working on.
Any RSV treatment or vaccine must go through a fine line to be useful in clearing away the infection, but not cause negative consequences. Mistakes have been made in the past: previous attempts at an RSV vaccine in the 1960s resulted in children becoming seriously ill.
But now that RSV immunity is much better understood and understood, vaccines are at least in development. Several are currently in clinical trials in the hope that we can finally protect all children from RSV-induced bronchiolitis.