Summer Flu, RSV in July, ‘Super Colds’?


Richard Martinello, MD, professor of medicine and childhood infectious diseases at Yale University, doesn’t expect to see a child hospitalized with respiratory syncytial virus (RSV) in the middle of summer. The disease, which particularly affects infants and the elderly, is known as the “winter virus”.

But not this year. Yale Children’s Hospital in New Haven has seen an increase in admissions of children with RSV over the past few weeks, he said. Although the numbers are small, they are unusual, he says, “because we usually see zero at this time of the year. For lack of a better term, it’s weird.”

Similarly, William Schaffner, MD, professor of infectious diseases at Vanderbilt University School of Medicine in Nashville, says RSV is on the rise there. Tennessee is one of 10 states participating in the CDC’s surveillance system, which tracks flu, RSV, and COVID-19.


He says RSV cases have increased by at least a third in the last week, including all age ranges. At this time of the year, he says, “we shouldn’t have RSV.”

RSV isn’t the only virus that thrives out of season or behaves strangely. Since the start of the pandemic, flu seasons have been out of whack—sometimes there were hardly any, and other times they went way beyond “normal” seasons. Some experts say that one of the “B” flu strains may have already died out, while others say it will return.

Severe colds – what some call “super colds” – also seem to have increased in recent months with warm weather, although this evidence is mostly based on personal experience and not scientific evidence.


Trying to explain these non-seasonal fluctuations has sparked a heated debate among epidemiologists and virologists, Schaffner said, and debate continues about whether human behavior and habits or the seasons play a big role in the transmission of viral diseases, Schaffner said.

In addition, scientists are also studying interactions between the SARS-CoV-2 virus that causes COVID-19 and other viruses. When people get COVID-19 and other viruses at the same time, does that make COVID-19 more severe or less severe? Research is conflicting.

Summer 2022: a repeat of 2021?

RSV: Most children become infected with the virus by age 2, and although the disease is generally mild, about 58,000 children under 5 years of age are hospitalized each year. The CDC reported that during the pandemic, the number of RSV cases decreased from January to April 2020 and then remained at a “historic low” of less than 1% of RSV positive results per week over the next year.

But cases started to rise in April 2021.

“We had an unusual summer last year,” Schaffner says. After the quarantine ended, to everyone’s surprise, the number of RSV infections increased.


This increase led to the release of a CDC health advisory in June 2021 reporting to physicians and caregivers of an increase in “off-season” cases of RSV in parts of the southern US, and recommending more extensive testing for RSV in patients with respiratory illness but tested negative for COVID.

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The CDC has warned that due to the decrease in RSV circulation during the winter of 2020-2021, older infants and young children may be at higher risk of RSV because they have not been exposed to normal levels of RSV during the previous 15 months.

What about 2022? “At the moment,” Schaffner says, “it looks like we’re having a repeat [of 2021].”


On Twitter, other pediatricians, including those from Maine and Texas, reported an increase in RSV cases this summer.

Influenza: From October 2020 to May 2021, influenza activity was lower than in any previous influenza season since at least 1997, according to the CDC.

In late 2021, researchers speculated that one flu line, known as B/Yamagata, may have died out.

According to the CDC, the 2021-2022 flu season was moderate, but it consisted of two waves, with the second wave dragging on longer than the previous ones. While flu activity is declining, the CDC said last week that doctors should be on the lookout for flu infections throughout the summer.

Colds: In cold reports that are not based on science, several doctors say that they have more colds than usual during the summer and are more severe than usual.

Since the beginning of 2021, the number of common coronaviruses and respiratory adenoviruses has increased, and since June 2020, rhinoviruses have increased, according to the CDC.

Behavior against the seasons

Explaining the spread of viral respiratory diseases, infectious disease doctors take into account two points.

“First, the temperature and humidity in winter make some viruses survive longer, leading to longer periods of possible transmission,” says Dean Bloomberg, MD, professor of pediatrics and head of pediatric infectious diseases at the University of California, Davis.

“The other thing is the differences in people’s behavior: in the summer people spend more time outside, which leads to more distancing and [less] concentration of the virus due to the very large volume of air,” he says, and vice versa in winter.

How about a “super cold”? COVID-19 lockdowns and social distancing have greatly reduced people’s exposure to common viruses, such as those that cause the common cold, says Neil A. Mabbott, PhD, professor of immunopathology at the University of Edinburgh in the UK.

“It is believed that immunity to these cold viruses, acquired through natural infection, lasts for about 8 or 9 months or so,” he says. “Each winter, when we are exposed to new circulating variants of these viruses, our immunity gets a natural boost.”

This explains why most people get colds relatively easily. But with all the restrictions due to the pandemic and the use of hand sanitizers, most people have had limited exposure to other viruses, including the common cold. When people came out of lockdown, cold viruses began to circulate again.

“Our immune system was less able to deal with infection than before,” says Mabbott. “As a consequence, some of them may have experienced an increase in symptoms, giving the impression that they were infected with a ‘super cold’.”

“The colds themselves are probably no different from what we had before the pandemic,” says Ian McKay, PhD, a virologist at the University of Queensland, Brisbane, Australia. “But there could be more. So I doubt it’s “super cold” as much as “super perfect circumstances”.

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These super-ideal circumstances include people gathering after lockdown, he says; lack of immunity in newborns; viruses that have remained, albeit at a low level, but continue to mutate; and our waning immunity to the range of viruses we commonly encounter.

While the lack of exposure may partly explain why some viruses become unmanageable out of season, it’s probably not the only reason. For example, reduced circulation of RSV in the general population may also have reduced the transmission of immunity from mothers to infants, some researchers say, making these infants more vulnerable than usual.

Virus Interaction

Another thing that could be causing the different behavior of the viruses, Schaffner said, is that the SARS-CoV-2 virus might interact in some way with other respiratory viruses. “And if so, what kind of interactions?”

Many researchers are studying this and how co-infections with other respiratory illnesses, including the common cold and flu, can affect the course of COVID-19. Some studies have shown that T cells — a source of deeper cellular immunity in humans — produced after a cold “may also confer cross-protection in some people against COVID-19.”

But another study found that immunity against the coronaviruses that cause the common cold could make COVID-19 more severe.

When researchers in the UK studied nearly 7,000 patients infected with COVID-19, including 583 people also infected with RSV, influenza or adenoviruses (which cause flu-like illness or colds), patients with the flu or adenovirus compared with others were at higher risk of death.

To be continued …

Exactly how COVID-19 will change what we know about other viruses remains to be determined.

Even before the pandemic, there had already been some shifts in the RSV, Martinello said. In Florida, for example, the RSV season is longer than in the rest of the country, mimicking the pattern in the tropics.

Will atypical patterns persist? “I assume it will settle down,” he says, working out some kind of pattern. At the moment there are many unknowns. “We still can’t answer if COVID will have some kind of seasonality.”


William Schaffner, MD, Professor of Infectious Diseases, Vanderbilt University School of Medicine, Nashville.

Richard Martinello, MD, Professor of Medicine and Pediatric Infectious Diseases, Yale University School of Medicine, New Haven, Connecticut.

Neil A. Mabbott, PhD, Professor of Immunopathology, University of Edinburgh, Scotland.

Dean Bloomberg, MD, professor of pediatrics and director of the Department of Pediatric Infectious Diseases at the University of California, Davis.

Ian McKay, PhD, virologist and associate professor at the University of Queensland, Brisbane, Australia.

Nature Reviews Immunology: “Respiratory syncytial virus after the SARS-CoV-2 pandemic – what’s next?”

Nature Reviews Microbiology: “Influenza Lineage Extinction During the COVID-19 Pandemic?”

CDC: “RSV in infants and young children.”


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