Experts explain the ‘perfect storm’ of endemic RSV and influenza

The headlines of the past few weeks are sounding the alarm about earlier and more serious events flu (influenza) and respiratory syncytial virus (RSV) outbreaks compared to previous years. Add COVID-19 to the mix and you have a dangerous mix of viruses for which many experts are urging caution and seeking explanations.

RSV and influenza “certainly get more attention, and they get more attention for two reasons,” said William Schaffner, MD, professor of preventive medicine and infectious diseases at Vanderbilt University School of Medicine in Nashville.

“The first is that they’re both extraordinarily early. The second is that they’re both spreading very, very quickly,” he said. Medscape Medical News.

RSV generally follows a seasonal pattern with peak cases in January and February. The two viruses tend to hit different parts of the country at different times, and that’s not the case in 2022.

“This is particularly striking for RSV, which usually does not affect the whole country simultaneously,” Schaffner said.

“Yes, RSV is causing far more hospitalizations and earlier than any season previously recorded in the United States,” according Centers for Disease Control and Prevention (CDC) figures on RSV hospitalizations, said Kevin Messacar, MD, PhD, associate professor at the University of Colorado School of Medicine and pediatric infectious disease specialist at Children’s Hospital Colorado in Aurora.

Although there may be some increase in diagnoses due to heightened awareness, the rise in RSV and influenza cases “is a real phenomenon for multiple reasons,” said Peter Chin-Hong, MD, professor at the University of California, San Francisco, Division of Health. infectious diseases.

With fewer COVID restrictions, people are moving more. Also, in the fall and winter, people tend to congregate indoors. Colder temperatures and lower humidity also contribute, Chin-Hong said, because “the droplets are just lighter.

“I think those are all factors,” he said. Medscape Medical News.

Paul Auwaerter, MD, MBA, agreed that there are likely several causes for the unusual timing and severity of RSV and influenza this year.

“Behavioral change is a major cause,” said the clinical director of the division of infectious diseases at Johns Hopkins University School of Medicine in Baltimore. More people returning to the workplace and children going to school without masks are examples, he added.

Less exposure to these three viruses also means there was less immune enhancement among existing populations, he said. This may lead to “larger susceptible populations, particularly infants and young children, due to the relative absence of circulating virus in recent years.”

A leading theory

Are we paying a price now for people who follow government decrees to mask up, stand out, and take other personal and public health precautions during the COVID-19 pandemic?

It’s possible, but it may not be the whole story.

“When it comes to RSV, I think the theory of isolation, social distancing, mask-wearing, and not attending school is very valid,” Schaffner said. “It’s everyone’s favorite [reason].”

He said he was confident the rise in RSV cases was due to previous COVID public health protections. However, he is “a bit more cautious about the flu, partly because the flu is so variable.

“As the flu people say, if you’ve seen a flu season, you’ve seen a flu season,” Schaffner said.

“There are a lot of debates,” he added. “No one can say for sure whether the immune deficiency or debt is a consequence of not having been stimulated and restimulated by the influenza virus for the past two seasons.”

“A Perfect Storm”

“Now you kind of have the perfect storm,” Chin-Hong said. “It’s not a good situation for COVID with the variants emerging. For flu, having not seen much flu in the last 2 years, we are probably more susceptible to infection.”

RSV cases increased in the summer of 2021, but now the weather is colder and people are interacting more closely. “And it’s very, very transmissible,” he said.

Chin-Hong also predicted that “even if we don’t have much COVID now, COVID will probably pick up again.”

The increase in RSV was unexpected by some experts. “This early flu is also a bit of a surprise and may be influenced by the fact that many of us come back and see each other up close, face to face in many closed environments,” Schaffner said.

He estimated that the 2022-2023 flu season started 4-6 weeks earlier “and took off like a rocket. It started in the southeast, quickly spread to the southwest and on the east coast. . I’m sure to go to the west coast if I haven’t already.”

A phenomenon by another name

Some refer to the situation as “immunity debt”, while others refer to it as “immunity break” or “immunity deficit”. Many doctors and immunologists have taken to social media to postpone the term “immunity debt”, claiming it is a misinterpretation that is being used to vilify COVID precautions, such as masking, social distancing and other protective measures taken during the pandemic.

“I prefer the term ‘immunity gap’…which is more established in the epidemiological literature, especially given how people have politicized the term ‘immunity debt’ recently,” Messacar said.

“For me, immune deficiency is a scientific observation, not a political argument,” he added.

In a Publication July 2022 in The LancetMessacar and colleagues stated that “decreasing exposure to endemic viruses has created an immune gap – a group of susceptible individuals who have avoided infection and therefore lack pathogen-specific immunity to protect against a future infection Decreased childhood vaccinations with pandemic disruptions in health care contribute to this immune deficiency for vaccine-preventable diseases, such as influenza, measlesand polio.”

The researchers noted that due to isolation during the pandemic, older children and newborns are being exposed to RSV for the first time. Going back to birthday parties, playing with friends, and going to school without a mask means “kids are exposed to RSV, and that’s probably why RSV is moving early and very, very noticeably in this now expanded pool of susceptible children,” Schaffner said.

What is the likelihood of co-infections?

With spikes in RSV, influenza, and COVID-19 cases each expected in the coming months, how likely is a person to get sick with more than one infection at the same time?

Early in the pandemic, co-infection with COVID and influenza was reported in people in some West Coast centers, Auwaerter said. Now, however, “the unpredictable nature of Omicron subvariants and the potential for further change, together with the never-before-seen significant decrease in influenza over 2 years, leaves little predictability.

“I think it’s less likely, given the extent of current immunity to SARS-CoV-2 in the population,” Auwaerter said.

“I worry most about viral co-infections … in people with compromised immune systems if we have high community rates of SARS-CoV-2 and influenza circulating this fall and winter,” he said. he adds.

Studies conducted during the pandemic suggest that co-infection with the SARS-CoV-2 virus and another respiratory virus has been be rare Where non-existent.

Schaffner said these findings align with his experience at Vanderbilt University, which is part of a CDC-sponsored network that tracks lab-confirmed RSV, influenza and COVID cases among hospitalized people. “Co-infections are, at least to date, very unusual.”

There must be an asterisk next to it, Schaffner added. “Looking back over the last 2 years, we’ve had very little flu and we’ve had shortened RSV seasons, so there hasn’t been a lot of opportunity for double infections to occur.

“So this year might be more telling as we move forward,” he said.

Future concerns

The future is uncertain, wrote Messacar and his colleagues in The Lancet“Crucially, the patterns of these recurrent viral outbreaks have been heterogeneous across locations, populations and pathogens, making predictions and preparations difficult.”

Chin-Hong used a horse racing analogy to illustrate the current and future situation. RSV is the lead horse and the flu is late but trying to catch up. “And then COVID is the dark horse. He’s behind the race at the moment – but all these variants give the horse extra extras.

“And the COVID horse is probably going to be very competitive with the favorite,” he said.

“We’re only at the start of the race right now,” Chin-Hong said, “that’s why we’re worried that these three [viruses] will be even more pronounced later in the year.”

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