Flu and respiratory viruses typically reappear in winter. However, since the beginning of the pandemic, the coronavirus known as SARS-CoV-2 has seen its “peak times” in summer as well as in winter. After five summers, have we understood why?
In recent months, both France during the Olympics, as well as Canada, the United States, and the United Kingdom, have seen the curve of confirmed cases start to rise again. Although we are far from the peaks of 2020 and 2021, this increase is nonetheless the opposite of what one might have expected: a respiratory virus statistically has a greater chance of spreading when more people are in enclosed spaces, which happens more often when the days become colder.
It seems that a dominant factor could be the speed with which new mutations of the virus continue to appear, warned the World Health Organization earlier this month. Our immune system may not necessarily identify them as the virus it already knows, and therefore would not activate the appropriate antibodies. This could explain why the virus continues to circulate so much — but it does not explain the summer factor.
Indeed, other viruses also undergo mutations. Any virus mutates. But not at the same rate, explains public health professor Andy Pekosz from Johns Hopkins School of Medicine in Maryland, in New Scientist. “It often takes a few years for mutations of the flu that can evade our immunities to accumulate… But with COVID, it seems to happen more than once in the same year.” As a result, other respiratory viruses may continue to circulate in summer just as much as SARS-CoV-2, but they are flying under the radar because their lower mutation rate, or their “milder” mutations, allows our immune systems to handle them.
Does this mean that these summer “peaks” are here to stay? Experts interviewed on this topic by New Scientist are “unanimous” in stating that we do not know this virus long enough to make a judgment. It is possible that over the years, the trend will shift towards more typical outbreaks, meaning only in winter. But no one can say when that will be.
Theoretically, getting vaccinated every year, as doctors recommend for more vulnerable people against the flu, could accelerate the disappearance of these summer “peaks”. The problem is that new versions of the vaccines typically arrive late: those from this spring were developed based on variants from 2023, which could make them less effective — thus giving the virus statistical chances to continue to spread widely.
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The Seasonal Dynamics of COVID-19: What Lies Ahead?
The emergence of SARS-CoV-2 has fundamentally altered the traditional dynamics of respiratory viruses, including their seasonal peaks. Historically, respiratory viruses thrived during the winter months, but recent trends indicate a concerning pattern: significant spikes in COVID-19 cases during the summer months across various regions, including France, Canada, the United States, and the United Kingdom.
As health authorities and experts analyze the situation, one predominant factor stands out—the rapid emergence of viral mutations. The World Health Organization has highlighted that the speed at which new variants of the virus appear plays a critical role in the persistence of COVID-19 cases. Unlike other respiratory viruses, which may take years to develop impactful mutations, SARS-CoV-2 shows a concerning frequency of changes, making it harder for our immune systems to recognize and combat the virus effectively.
While other respiratory viruses also mutate, the pace and nature of mutations associated with COVID-19 appear uniquely aggressive. This spike in mutations could mean that during the summer months, when traditional respiratory viruses also circulate, SARS-CoV-2 remains more virulent. Other viruses may recede in their impact, allowing COVID-19 to hold steady in the public domain.
Looking toward the future, experts remain cautious. The uncertainty surrounding these summer peaks and the potential for long-term trends is significant, as the scientific community has yet to fully grasp the long-term behavior of this virus. However, there is a consensus that annual vaccinations, akin to flu shots, could play a crucial role in mitigating these summer outbreaks. Yet, challenges remain: vaccine formulations often lag behind current variants, potentially diluting their effectiveness when urgently needed—and increasing the risk of continued viral transmission.
As the landscape of viral infections evolves, keeping pace with emerging trends and adaptations in vaccination strategies will be vital. The health of populations may depend on our ability to adapt swiftly to the rapidly changing nature of SARS-CoV-2 and competitors in the realm of respiratory viruses.