#16,206
After 18 months of almost no influenza - and very little other non-COVID respiratory illness - reported around the globe, there are concerns that seasonal flu, and other ILIs, could return with a vengeance this fall and winter.
As we've discussed previously (see here, here, here, and here), our recent lack of exposure to common respiratory viruses is a double-edged sword.
- In the short run, it makes it easier to identify COVID cases, lessens the burden on healthcare delivery systems, and avoids the enhanced risks due to dual infections.
- But at the same time, this lack of exposure allows our community immunity to these viruses to wane over time, potentially setting us up for serious epidemics when they finally do return.
One of the trends we've been watching over the summer has been the unexpected, and unseasonable, return of RSV (Respiratory Syncytial Virus) both here in the United States and around the globe. Normally, RSV peaks in the winter and spring, not the summer. A few, recent reports include:
UK PHE Warns On A Summer Uptick in RSV Infections
SSI: Denmark Also Reporting A Summer Surge In RSV
ESCMID: When Respiratory VIruses Return & New Zealand's RSV Resurgence
These increases have coincided with the lessening of COVID social distancing restrictions, and have raised concerns - including mid-July's UK Academy Of Medical Sciences: Looking Ahead To COVID-19 Over Winter 2021/22 & Beyond and a commentary appearing in the CMAJ called Potential resurgence of respiratory syncytial virus in Canada - that we could face a challenging winter ahead.
Three weeks ago Denmark's SSI (Statens Serum Institut) reported on their `Extraordinary' Summer Spike In RSV Cases, and returns today with an update that indicates cases are still very high, but have come down slightly over the past week.
They warn, as have others in recent weeks, that this winter could prove particularly challenging for healthcare delivery systems. I'll return with a postscript.
Slowdown in the RS virus epidemic, but still many infected and hospitalized children
The past month's outbreak of Respiratory Syncytial Virus (RS virus) is still in full swing. A small drop in the infection curve in the past week indicates a slowdown in the infection, but the epidemic may last for weeks yet. It can challenge an already pressured hospital system in the fall and winter. This is the prediction in a new risk assessment from the Statens Serum Institut.Last edited September 23, 2021
The late summer's growing epidemic has slowed down in the past week, but may continue for some time to come, according to the assessment from the Statens Serum Institut (SSI).
Denmark, like several other countries, has experienced a sharp increase in cases of RS virus in the wake of the reopening of society. In week 36 alone, over 1,300 cases were detected and in week 37 over 1,100. It is three to four times higher than what is usually seen per week when the typical winter seasons peak.
"In the past week, we have seen a small decrease in the otherwise sharply upward infection curve. This indicates a slowdown in the development of infection, but the unusual and high spread of infection with RS virus will probably continue for a while yet, ”says ward doctor, Lasse Vestergaard from SSI.
RS virus is usually a winter disease
RS virus usually occurs between December and March and 2021 is thus an unusual year. With the very early start, it is the expectation of the normal RS season being extended.
“Outbreaks of RS virus we typically experience in the winter months, and we therefore also expect that the epidemic this year will last longer than the normal 6-10 weeks due to the early start. How long the epidemic will last and whether we will see repeated waves of infection through the autumn and winter is difficult to predict, ”he says.
This is an unusual situation without precedent in Denmark. We have only limited experience from abroad recently to draw on. Therefore, a good basis for comparison is lacking, and this makes it difficult to predict with certainty how the current epidemic will behave, when it will peak and whether it will continue over the winter.
Based on the preliminary monitoring data, SSI estimates that this may be a very extensive societal infection, of which we only see the top. Combined with the upcoming flu season and any increases in covid-19 infection rates, it could challenge health care in the coming months.
Read SSI's risk assessment for RS virus here.
Both timing and scope are unusual
As outbreaks of RS virus are usually seen in winter, similar to other respiratory infections, the timing of the current outbreak is quite unusual. At the same time, there are unusually high infection rates, even if one compares with other years' peak for infection in the winter months.
The positive percentage among the people tested is very high - 46% and 43% in the last two weeks - and at the same time the number of people tested is still lower than what is tested during normal winter outbreaks of RS virus. This suggests that there is widespread RS virus infection in the community and a large number of blackouts.
"We are in a somewhat unknown country with this unusual development of infection, which we believe may be related to the fact that the youngest children have not developed sufficient immunity, after a winter where we had virtually no RS virus due to covid-19 the restrictions, ”explains Lasse Vestergaard.
In the winter of 2020/2021, Denmark had a very low incidence of a large number of respiratory infections due to the introduced restrictions and hygiene measures against covid-19. Those restrictions have now been lifted and children and adults are once again interacting freely with each other. This also applies to children in crèches, kindergartens and schools.
Due to the low exposure last winter, and thus the lack of acquired immunity to RS virus in the entire population in the last season, the group of even slightly older children will now be extra susceptible to RS virus.
Respiratory viruses can challenge health care in the fall
RS virus is mainly detected in children, but only in a few adults and the elderly. This is because otherwise healthy infected adults will typically only have mild cold symptoms. However, in contrast to the typical RS virus seasons in winter, where the infection is particularly seen among children under 1½ years, relatively more children with RS viruses are now seen between the ages of 2, 3 and 4 years.
Many hospitalized children with RS virus are currently being reported from the country's pediatric wards. SSI estimates that simultaneous outbreaks among children of RS virus and other respiratory viruses such as influenza and covid-19 can further strain the pediatric wards during the winter months. This is especially true among the youngest children under 2 years of age, as these children are not vaccinated against the two diseases and at the same time are at particular risk of becoming seriously ill from the RS virus.
The RS virus is not routinely tested for mild illness, but rather for more serious illness and consideration for hospitalization. Children with mild symptoms of respiratory infection should still be tested for covid-19.
RS virus is transmitted by droplet infection and infection can be limited byFollow the development here
- To adhere to the Danish Health and Medicines Authority's guidelines against respiratory infections (good hygiene with frequent hand washing, spraying, cleaning, venting, etc.)
- Staying home when you are sick with respiratory symptoms including colds
- That the population is well informed about RS virus - including that elderly and debilitated people can develop serious disease with RS virus.
Surveillance of RS virus has been intensified. Here you can follow the latest figures on RS virus.
Although I have my reservations, there are recent models suggesting that COVID may have peaked, and the number of COVID cases, hospitalizations, and deaths are likely to decline over the next six months (see NPR Is The Worst Over? Modelers Predict A Steady Decline In COVID Cases Through March).
As much as I'd like these predictions to be true, models - so far, at least - haven't done a particularly good job in predicting where this pandemic is headed. Eventually COVID will peak, and hopefully that time is now, but it is far too soon to pop open the champagne bottles.
Even if COVID does decline over the next few months, the return of influenza and other respiratory viruses could significantly impact healthcare delivery this winter. All reasons why getting the flu vaccine on top of the COVID shot, wearing masks in public, and avoiding `risky' behavior, all make sense going into this fall and winter.
