COVID-19 may indeed become a seasonal illness with predictable patterns of infection— but it’s not there yet, according to epidemiologists and infectious disease experts.
While the virus has had some element of seasonality since it first came into the world, other factors, including variant evolution, population immunity, and behavioral changes, have made seasonality less apparent. We have seen this in the form of previous seasonal Covid surges. Surges have been linked to when variants commonly occur. Connecting variants and outbreaks comes down to the role of these mutations, directly linking the variants present at a certain time and place with the Coronavirus’s reproductive number, known as R for short.
R is a way to quantify the intensity of an infectious disease outbreak. It stands for how many additional people an infected person will spread the germ to. By incorporating genome sequencing data with information about transmissibility, this creates a kind of early warning system, allowing the forecast of spreading events. In the real world, advance warning like this could inform public health decisions about social interventions. People can prepare for predicted outbreaks.
Add to that the fact that immunity against infection wanes for both the previously infected and the vaccinated, which makes Covid surges much less predictable than the virus the world has wanted it to become since the beginning, influenza (flu).
The disease may fall into a more predictable rhythm once the population has more immunity and as people go back to their pre-pandemic lives, but experts agree that this will likely take a few more years to achieve.
Hoping for the predictability of the flu
The hope around Covid having “seasonality” in the near future may have something to do with how predictable the flu virus is. Each year, the US can expect relatively low mortality and morbidity when it comes to the flu, anywhere between 12,000 and 60,000 deaths–with 140,000 and 810,000 hospitalizations, according to the CDC.
James Lawler, MD, MPH, of the University of Nebraska Medical Center’s Global Center for Health Security in Omaha stated that regarding predictability, “it’s just not possible to fit the square peg of SARS-CoV-2 into the round hole of influenza just yet.”
It’s because they’re”vastly different viruses,” he noted.
Influenza frequently changes, requiring annual vaccination, but it shifts, developing larger mutations that can lead to more virulent, pandemic influenza causing greater mortality— less frequently.
Whether you call these mutations a change, shift, or drift, or continuous evolution of the virus, it doesn’t seem to be slowing down.
Experts agreed that evolution of SARS-CoV-2 actually appears to be accelerating, given what’s been observed with the evolution of variants in the Omicron family.
That could indicate that variants will evolve at a more rapid rate, which may not correlate with the seasons. That’s happening now in the northeastern US, where BA.2.12.1 has started to take off, and is contributing to a surge that was not seen this time last year.
“Right now, we have a highly infectious virus, and we have waning immunity,” said Ali Mokdad, PhD, of the Institute for Health Metrics and Evaluation at the University of Washington in Seattle. “So people are susceptible to the virus even in summer.”
The virus is evolving rapidly and will continue to. While this preliminary evidence relied on a small number of genome sequences, it was all the data available from the early stages of the pandemic. As the pandemic continues, labs are sequencing thousands of genomes across the globe weekly. Scientists have replicated initial estimates using 20,000 genomes from the UK and arrived at the same observation – new variants led to more transmission, variants are continuing to expand and will continue to increase in prevalence as the pandemic continues.
That doesn’t necessarily mean we’ll see more serious disease–or, if making the maligned comparison to flu, a big shift that causes a huge surge in hospitalizations and death. Evolution would likely favor more transmissible or more immune-evasive variants, but not a variant that keeps people in bed.
If the Alpha variant was a shift from the original strain, Delta a shift from Alpha, and Omicron a shift from Delta, it’s possible Omicron may represent a transition to evolve, which could make it behave more like the four other Covid strains that currently circulate in the US.
Learning from other Covid variants
Those four variants, Alpha, Beta, Delta, and Omicron, have seasonality and may be a better model for the future of COVID-19 in the US. They circulate throughout the year at relatively low levels, but cause peaks of infection in the winter months, as substantial parts of the country head indoors to escape the cooler weather.
There has already been some element of seasonality [with SARS-CoV-2], but it’s not as evident as it is with the other four coronaviruses that circulate every year. That may be due to the fact that until recently, there was very little immunity in the population, and that may have prevented the stark seasonality from being apparent.
Those coronaviruses are also capable of reinfecting people. That means SARS-CoV-2 is most likely going to continue to evolve and continue to become immune evasive in order to reinfect us, just like other members of the coronavirus family do.
Experts agree that pointing out the comparison could have helped health officials better temper expectations around Covid vaccines.
We don’t have lifelong immunity to any of these coronaviruses, and that probably should have given us a pretty good clue that we were not going to achieve that with SARS-CoV-2, either from natural infection or from vaccination. We should now be prepared for this phenomenon of having to get periodically boosted.
CDC Director Rochelle Walensky, MD, MPH, said she anticipated that COVID would “probably” become a seasonal virus.
There’s no doubt over the last few years that the US saw its highest peaks in winter, in early to mid-January.
Most experts agree that COVID-19 may be headed toward seasonality. They’re just not prepared to say so definitively, as SARS-CoV-2 has thrown so many curveballs in the past.
To put it into perspective, it was just over a year ago when Omicron had just emerged on US shores. The challenge experts face is that they have never seen this subvariant activity with Alpha, Beta, or Delta, so who could have predicted even 6 months ago where we’d be today?
That being said, it’s important to be aware of all variants and sub-variants to stay informed on Covid news and health information updates.
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