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.

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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. "The off-season resurgence in seasonal respiratory viruses now potentially poses a threat to vulnerable infants," said Dr. Pascal Lavoie, BC Children's Hospital Research Institute and the University of British Columbia, Vancouver.

During the COVID-19 pandemic, Canada, like other countries, has seen very few cases of RSV, with only 239 positive cases between August 29, 2020, and May 8, 2021, compared with 18,860 positive tests in a similar period the previous year (between August 25, 2019, and May 2, 2020). The virus seemed to disappear over the last year. However, an increased number of cases of RSV in Canada this summer, as in other jurisdictions, could stretch healthcare resources in pediatric intensive care units (ICUs). Most pregnant women and very young infants did not develop immunity in the previous season, so children may develop more severe illnesses this year.

The researchers in the Canadian Medical Association Journal suggested a continued emphasis on handwashing and basic hygiene measures and other protective measures such as breastfeeding when possible; testing to confirm RSV when required; planning by pediatric ICUs to manage increases in severe RSV cases and administering preventive treatment to highest-risk infants if cases increase.

While the levels of influenza and other non-COVID respiratory viruses were at historic lows during most of 2020 in the US, the virus causing the common cold is having an out-of-season resurgence in 2021, according to a new report from the Centers for Disease Control and Prevention (CDC). According to the experts, the protective measures people took against COVID-19-masking, distancing suppressed the virus. "Clinicians should be aware that respiratory viruses might not exhibit typical seasonal circulation patterns and that a resumption of circulation of certain respiratory viruses is occurring," the CDC report said.