Respiratory viruses in young children likely to resurge, warn researchers Cases of respiratory syncytial virus (RSV) have risen sharply in Australia and, more recently, in the US as pandemic public health measures have been relaxed. Toronto: As Covid-19 physical distancing measures are being relaxed in many countries, there can be a resurgence of a childhood respiratory virus, researchers have warned. Cases of respiratory syncytial virus (RSV) have risen sharply in Australia and, more recently, in the US as pandemic public health measures have been relaxed. RSV affects the lower respiratory tract and can cause serious illness and death. Before the Covid-19 pandemic, about 2.7 million children worldwide were infected with RSV each year, and it was the fourth most common cause of death in young children.