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The pandemic is making a comeback in the northern hemisphere, highlighting the benefits of
vaccination.
Photo by Robert Anic/PIXSELL/Alamy
Restrictions to curb the spread of COVID-19 have significantly slowed the spread of
other respiratory diseases.
Influenza and respiratory syncytial virus (RSV) — a seasonal virus that typically causes mild cold-like symptoms but can be dangerous for young children and older adults — all but disappeared
in 2020 and early 2021.
Now, in the Northern Hemisphere, respiratory syncytial virus is surging, and flu hospitalizations in the United States are higher
than at any time since 2010.
Why are these surges happening now? What will happen in the coming winter?
Scott Hensley, an immunologist at the University of Pennsylvania in Philadelphia, said: "These viruses are making a comeback, and the comeback is very ferocious
.
" "In terms of influenza, this year is probably the highest number of
infections of all years.
"
That's because the population is "weaker in terms of immunity than we would expect in most years,"
Hensley said.
Normally, a child becomes infected
when they are two years old.
Now, "you're going to have three- or four-year-olds who have never seen RSV
.
" ”
For older children and adults who have been previously infected, the problem is reduced
immunity.
In the absence of exposure to the virus, antibody levels drop.
John Smith, an immunologist at Imperial College London? John Tregoning says that in a typical year, "we might be exposed to a small amount of the virus, but your body will push it back
.
" But "this asymptomatic ascent may not have happened in years past.
"
But restrictions on COVID-19 began to be lifted last year
.
So why did the surge begin only now? Hansley feared the flu and RSV would bounce back
last year.
But the flu season in the Northern Hemisphere has been generally mild
.
While RSV infections did increase, the peak was lower than in pre-pandemic years, occurring in the summer of 2021 — odd timing points that may have helped curb the spread of the virus
.
Virginia Pitzer, an epidemiologist at the Yale School of Public Health in New Haven, Connecticut, said factors such as temperature and humidity played a role in the spread of the virus, and that peak "was not an environmentally favorable period for RSV.
"
In August 2021, researchers in France coined the term "immunity debt" to describe the decline
in immunity at this population level.
On Twitter, the word took on a life
of its own.
Some believe this means that lack of exposure to pathogens such as RSV and influenza has irreparably damaged the immune system, a view called "nonsense,"
a statistic called Matthew Miller, an immunologist at McMaster University in Hamilton, Canada.
Some scientists have also hypothesized on social media that the surge in respiratory syncytial virus hospitalizations could be the result of immune deficiencies caused by SARS-CoV-2 infection, which makes people more vulnerable to other infections
.
But Miller said he also hasn't seen any evidence of this, and the surge in hospitalizations may be due to a large number of people who have not been exposed to radiation
in the past few years.
"There are also slightly more naïve people who are at risk
.
So you have more numbers coming into the system
.
”
It's hard to predict what the new normal for seasonal viruses will look like
.
If many susceptible people are infected in the coming months, next year's flu season could be milder because some immunity debt has already been "paid off.
"
But it's unclear whether COVID-19 will become a seasonal illness like the flu and RSV, or whether it will continue to see sporadic peaks
throughout the year, as it has in the past.
There's still a lot researchers don't know about seasonal viruses
.
For example, COVID-19 restrictions appear to have had little impact on a seasonal virus – rhinovirus – the most common cause of colds – for reasons that are not fully understood
.
Miller said this may be because of their hardiness
.
They dry less easily and can survive longer in the environment
.
Another open question is how these viruses compete and interfere with each other
.
Infection with one virus can cause a strong innate immune response, which may prevent infection with another virus
.
Hensley noted that last year's first wave of flu dwindled
shortly after the surge in the omega virus.
Perhaps the Omicron infection offers some short-term protection
against the flu.
Or, the explosion of the omicron virus simply gets people to wear masks and keep their distance
.
Pitzer expects that next year's peaks and troughs may be more like those before
the pandemic.
She didn't make any bets
.
But she said: "I do expect that this winter may be the last unusual winter
.
"
