Respiratory Syncytial Virus (RSV) is a major cause of acute respiratory tract infections, particularly in young children. RSV infection is estimated to cause about 14,000 annual deaths in U.S. adults over age 65. Globally, RSV affects an estimated 64 million people and causes 160,000 deaths each year.
Clinical Manifestations of RSV
RSV typically results in bronchiolitis, characterized by symptoms such as respiratory distress and cough, and varying degrees of hypoxia due to airway congestion in older children. In young infants, it can also present as apnea. Newborns receive some degree of protection against severe RSV disease through maternal antibodies transferred via the placenta, but this immunity wanes quickly, peaking in vulnerability at around one to two months of age. Most children are infected by RSV by their first or second birthday.
RSV in Adults
Seasonality and Transmission of RSV
Before the COVID-19 pandemic, RSV infections followed a predictable seasonal pattern. In temperate northern regions, RSV epidemics consistently peaked during winter months. In tropical and subtropical regions, transmission peaked during rainy seasons. Seasonal changes linked to environmental, demographic, and human behavioral factors, such as traveling, indoor gathering, local population density, outdoor temperature, and humidity, largely influence this pattern. These epidemics typically follow a biennial oscillation pattern, likely driven by ecological factors and a population-level immunity that lasts between six and 12 months.
Impact of the COVID-19 Pandemic on RSV
The COVID-19 pandemic dramatically affected RSV transmission patterns. Following the implementation of non-pharmaceutical interventions (NPI) like social distancing and mask-wearing in early 2020, RSV cases plummeted worldwide. However, as these measures were relaxed, there was an off-season resurgence of cases in many regions. Australia, for example, experienced an unusual surge in RSV cases during the summer of December 2020 to February 2021, with a shift towards older children presenting with symptomatic infections. This resurgence varied in intensity and clinical severity across different regions, with Western Australia and the Melbourne area reporting peak cases at different times. Other areas of the world also reported similar resurgences.
The Immunity Debt Theory in RSV: A Critical Examination
Evidence for the Theory:
- Increased RSV cases: Following pandemic restrictions, several countries have experienced atypical RSV seasons with higher than usual case numbers and hospitalizations, particularly in younger children.
- Limited prior exposure: Lockdowns and social distancing measures during the pandemic likely led to reduced circulation of RSV, potentially leaving a larger portion of the population, especially young children born during the pandemic, susceptible to infection.
- Mathematical models: Some modeling studies suggest that a decrease in RSV circulation during the pandemic could lead to a temporary “immunity debt” and a subsequent increase in cases when restrictions are lifted.
Potential Explanations:
- Immunity debt: The reduced exposure to RSV during the pandemic could have led to a delayed development of natural immunity in young children, making them more vulnerable to severe infection.
- Changes in viral behavior: Some experts suggest the virus itself may have adapted during the pandemic, becoming more transmissible or virulent.
- Other contributing factors: Increased social mixing, decreased mask use, and potential changes in respiratory hygiene practices could also be playing a role in the current RSV surge.
Limitations of the Theory:
- Limited data: The theory is primarily based on observational data and mathematical models, which require further research and data collection to be definitively confirmed.
- Alternative explanations: The observed increase in RSV cases could be due to other factors, such as changes in seasonal patterns or improved surveillance.
- Complexity of immunity: The immune response to RSV is complex and involves both humoral (antibody) and cellular immunity. The theory primarily focuses on antibody levels, neglecting the role of other immune factors.
Interactions Between SARS-CoV-2 and RSV
The potential interaction between SARS-CoV-2 and RSV has been a subject of interest. Studies have shown varying results regarding co-infections. For instance, a study from the UK reported co-infections with RSV or influenza in 3.1% and 3.2% of SARS-CoV-2 cases, respectively. A U.S. study found no cases of SARS-CoV-2 and RSV co-infection among 37 RSV cases during August–October 2021. However, another U.S. study during an RSV surge between March and August 2021 found that only 1.4% of RSV cases had co-infection with SARS-CoV-2. In Italy, no cases of co-infection were observed despite RSV being detected in 12.8% of cases. Canadian data from the British Columbia Children’s Hospital indicated a 1.8% and 1.7% co-infection rate during the 2021–2022 and 2022–2023 RSV seasons, respectively.
Immune Dysregulation Post-COVID-19
Post-COVID-19 immune dysregulation has been proposed as a factor increasing susceptibility to other respiratory viruses, including RSV. Studies have shown changes in immune cell populations and activation markers in COVID-19 convalescents, suggesting potential long-term immune alterations through . However, the clinical relevance of these findings is not fully established.
Increased RSV Virulence
The hypothesis of increased RSV virulence due to the pandemic conditions has been explored but not substantiated by current data. Genomic analyses of RSV strains during surges have not indicated the emergence of a more transmissible or virulent lineage【.
Other Contributing Factors
Changes in health-seeking behaviors, testing practices, and health system dynamics also played a role in the changing epidemiology of RSV. The decrease in pediatric emergency department visits, delayed medical consultations, and changes in societal approach towards respiratory illnesses are notable factors.
Conclusion
The interplay between RSV and COVID-19 presents a complex scenario influenced by various factors, including changes in human behavior, healthcare practices, and potential biological interactions between viruses. Understanding these dynamics is crucial for developing effective public health strategies to manage and prevent RSV, particularly in the context of emerging global health challenges.
TABLE 1 – Respiratory syncytial virus (RSV)
Respiratory syncytial virus (RSV) is a common respiratory virus that causes mild, cold-like symptoms. People who contract RSV usually recover in around a week without the need for medical treatment. However, in infants under six months of age, people over 65, and people with a compromised immune system, RSV can cause severe illness and death.
Symptoms usually appear two to eight days after being infected.
RSV affects different age groups differently, but the most common symptoms of the condition include:
- Cough
- Sneezing
- Fever
- Runny nose
- Wheezing
Infants who contract RSV may develop different symptoms such as:
- Irritability
- Decrease in appetite
- Changes in their breathing pattern
- Apnoea (temporary cessation of breathing, especially during sleep)
In children under 5, RSV can also cause:
- Rapid breathing
- Trouble swallowing
- Sepsis
Adults with RSV may also experience:
- Sore throat
- Headache
- Congestion
- Fatigue
Key facts
Risk for people
RSV can affect people at any age and almost all children will be infected with RSV by the time they are two years old. While most cases are mild, RSV can worsen existing medical conditions and cause serious complications that can be life-threatening. Complications of severe RSV infection include bronchiolitis, the inflammation of the small airways in the lung, and pneumonia, an infection of the lungs.
In the EU, Norway and United Kingdom, RSV is responsible for the hospitalisation of around 213,000 children under five with some requiring intensive care, and roughly 158,000 adults each year. One in twenty elderly people in Europe contract RSV every year.
Those most at risk include premature infants and those under six months old, people over 65 and those with weakened immune systems or pre-existing conditions such as diabetes, heart disease, and lung disease.
In infants and young children, the signs of severe RSV infection that require urgent medical attention are linked to difficulty breathing. Short shallow breaths, flaring of the nostrils when inhaling, noisy breathing, pauses in breathing, and caving of the chest signify the need for urgent medical care. In addition, parents should look for blue or grey colouring of the lips, mouth or fingernails as this is a sign of critically low blood-oxygen levels.
Infants may also develop sepsis, an infection of the bloodstream that can cause a variety of symptoms including a drop in blood pressure, increase in heart rate and fever.
How it spreads
RSV spreads from person to person via particles and droplets released into the air when an infected person breathes, speaks, coughs or sneezes.
Close contact such as kisses from parents to children can also spread the virus.
RSV can also spread when respiratory droplets land on surfaces that other people touch. These people may then pick the virus up on their hands and become infected when they touch their nose, mouth or eyes. This is a common means of transmission for infants and young children who touch infected surfaces and toys or put them in their mouths.
Vaccination and treatment
In 2023, the European Union approved the first RSV vaccine suitable for protecting infants up to six months of age as well as two vaccines for older adults. When given to a mother during pregnancy, the antibodies generated in response to the vaccine can cross the placenta to the foetus, protecting the child for up to six months following birth.
Mild cases of RSV do not usually require any treatment as people recover on their own after a few days. Infants under six months may require a hospital stay to monitor their breathing and oxygen levels. In severe cases, hospital treatment can include supportive care, breathing support and anti-viral medication alongside specific treatments for complications that may arise.
In some cases, children under 2 may be given medication by their doctor to reduce their risk of severe disease should they become infected.
Protective measures
In addition to vaccination, general prevention measures are the same as for most other respiratory viruses. These include:
- avoiding close contact with sick people
- washing or cleaning hands frequently
- avoiding touching your eyes, nose or mouth.
- maintaining good respiratory hygiene and cough etiquette
reference link : https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(23)00266-3/fulltext#:~:text=Respiratory%20Syncytial%20Virus%20(RSV)%20is,100%2C000%20deaths%20each%20year%2C%20worldwide.
https://www.niaid.nih.gov/diseases-conditions/respiratory-syncytial-virus-rsv#:~:text=RSV%20infection%20is%20estimated%20to,causes%20160%2C000%20deaths%20each%20year.
https://www.ecdc.europa.eu/en/respiratory-syncytial-virus-rsv
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