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Gearing up for flu season in 2020, some experts feared
we were in for a double whammy of both influenza and COVID-19.
Not only would there be a so-called “twindemic” of two harmful respiratory viruses,
but people with symptoms would have to be tested for not one but two diseases.
But some experts were surprised when the 2020-2021 flu season came and went
with far fewer cases than usual in the world.
One big reason that the twindemic didn’t happen is that social safety interventions
to control the spread of COVID-19 also appear to have
reduced influenza transmission.
But whatever the reason for the flu's no-show in 2020,
experts say that it poses challenges for flu vaccine development.
In other words, we could be in for a bad season.
See, ever since the mid-20th century when scientists started to realize that
influenza mutates regularly, global influenza preparedness has worked
like a well-oiled machine.
In over a hundred countries, government officials and scientists share data
year-round on emerging mutations in the influenza virus and
coordinate the next steps.
Officials keep an eye on what’s happening in the northern hemisphere to predict
and manage what will happen in the southern hemisphere, and vice versa,
to optimize vaccine strategies.
Unlike other viruses such as measles, influenza mutates quickly.
That’s because of influenza viruses’ segmented genome structure,
and when two or more different influenza viruses infect the same host,
they can swap genome segments and create new mutants.
And this swap happens more often in hosts like pigs,
so researchers call them mixing vessels for the flu.
Basically, these animals can catch multiple flu viruses from
different species at the same time.
When the viruses infect the same individual animal,
the viruses can trade their DNA to create new mutations.
Part of influenza preparedness includes constant monitoring of flu circulating in
animals to catch any new strains with the potential to spill over,
moving from one species to another, like humans nearby.
And for decades, researchers have had about a
six-month head start ahead of each flu season.
They’ve also had plenty of virus samples to work with from
people who tested positive for the flu.
Those samples help officials determine which version of the virus
will dominate the season.
This past nonstarter flu season basically throws a
wrench in that well-oiled machine.
See, just because there weren't a lot of flu cases in humans doesn’t necessarily
mean influenza viruses haven’t been doing their usual mutations in animals.
Which doesn’t mean it’ll get bad now,
but it could be a problem in the future if the viruses are transmitted to humans.
And now, there’s a hole in the usual year-round samples of the circulating strains.
But the lack of surveillance and influenza sequence data isn’t the only
problem for the upcoming flu season.
Even though influenza mutates, scientists think that people who have been
infected or vaccinated may contribute to the herd immunity for the next flu season -
or maybe even the one after.
So even though people still received the flu vaccine in 2020-2021,
the fact that not as many people got sick with the flu last year means
there are likely more people who are susceptible to getting sick this year.
For the optimists in the house,
there are some potential silver linings to the influenza no-show.
For one, it appears that combining social safety interventions
and yearly vaccines can stave off the flu.
All of this isn’t to say that we’re doomed to an unavoidable killer flu season!
It just means things will be trickier.
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