Why Covid-19 is spreading this summer

COVID-19 does not follow normal seasonal patterns like other respiratory viruses and waves of infection can occur at any time of the year.

Epidemiologists at the Centers for Disease Control and Prevention (CDC) have noticed a surge in COVID-19 cases and hospitalizations every July for the past four years, a trend they’ve dubbed the “summer surge.”

This summer, the US has reported particularly high rates of COVID-19 infections in Arizona, California, Hawaii and Nevada. These western states: The positive rate reached 15.6%. The week ending July 6 saw a 1% increase from the previous week, according to the CDC survey. show Virus rates in wastewater are also rising again.

A similar trend is seen on the other side of the Atlantic, by According to the UK Health Security Agency, the rate of positive coronavirus tests rose from 4% at the end of March to 14% at the end of June.

He directs the Virus and Emerging Pathogens Program at Ohio State University. FLiRT variantsThe latest COVID-19 virus has struck a fine balance between being able to attach to cells while still evading the immune system, which is resulting in many new infections.

“Older people and those with immunosuppressed conditions are particularly vulnerable to new variants because they have weakened immune responses to vaccination or natural infection,” Liu said. He explained that experts recommend these groups receive a booster shot containing the XBB.1.5 monovalent vaccine, which is designed to target the Omicron XBB1.5 variant of COVID-19. Coming in 2022.

Given the need to protect the most vulnerable in society, studying these ever-emerging variants remains crucial to updating the world’s COVID-19 vaccines. Based on Liu et al.’s study, US Regulators And that who They were able to make specific recommendations on new vaccine targets based on the latest spike protein mutations, just in time for the rollout of the latest Covid vaccines in the autumn.

But that’s still pretty much it for scientists monitoring how SARS-CoV-2 is evolving and changing. Unpredictable When will the next notable strain emerge? The most common respiratory infections, such as influenza and respiratory syncytial virus (RSV), Follow seasonal patternsThe new coronavirus infection is said to increase sharply from autumn to winter and subside from spring to summer, but it has not yet settled into this characteristic cycle.

Given the recent summer outbreaks, it remains to be seen whether COVID-19 will truly become a seasonal virus, and if so, how long it will take.

According to epidemiologists and medical researchers, there are three main factors that drive the outbreak of an infectious disease: the virus itself, the number of susceptible people at a given time, and the conditions in which the virus can spread.

“Seasonality is a common feature of many viruses, most notorious being influenza, which spreads every winter,” says El Hussein Shamsa, an internist at University Hospitals in Ohio and who published the study in 2023. COVID-19 patterns throughout the yearIn this case, it’s thought that environmental and behavioral factors may lead to a weakening of immunity during the winter months and a greater spread of the flu virus, he says.

But influenza never goes away entirely. Akiko Iwasaki, a professor of immunobiology at Yale University, said the summer coronavirus outbreak was likely exacerbated in part by factors such as crowds at festivals and concerts and heavy use of air conditioning, which dries out the air and encourages the virus to spread.

For example, British transmission experts have suggested that increased gatherings in crowded pub gardens and bars after this summer’s Euro 2024 soccer tournament are likely the cause of many of the country’s recent COVID-19 cases. Latest Data “Our findings suggest that cases in June peaked around the week of 17 June, just after England’s first match,” said Paul Hunter, a consultant and professor of virology at the University of East Anglia, “and then cases started to rise again in July as England progressed through the tournament.”

But the question remains: why is this year-round effect seen primarily with COVID-19 and not with other respiratory infections? Scientists think it’s because herd immunity is much higher for many of the usual seasonal viruses, such as influenza, rhinovirus, and respiratory syncytial virus. One reason is that these viruses have been around for much longer and therefore transmit in more ideal conditions, which only occur during the fall and winter. Temperatures dropSchool reopens, People are gathering indoors more often. (Click here for details Talking and singing spreads disease.

Because COVID-19 is still a relatively new virus, sterilizing immunity — the body’s ability to eliminate pathogens before they can multiply — is quite low. Scientists feel this is exacerbated by low vaccination rates, making herd immunity more dependent on how many people have been infected in the most recent outbreaks.

Shamsa said the current variant of FLiRT is Common immune escape mutations With the COVID-19 variants that caused a surge in cases in the winter of 2023 as a backdrop, it is now possible to take full advantage of weakened immunity. According to the CDC:As of July 7, only 22.7% of people aged 18 and older in the United States have received a COVID-19 vaccine, compared with 48.2% for the flu. As a result, people who didn’t get COVID-19 over the winter likely have little immunity to the FLiRT variants that are causing the current surge in cases, Hunter said.

“When it comes to COVID-19, I think many people don’t want or need the vaccine, which means herd immunity will rise and fall more or less simultaneously depending on the frequency and strength of recent waves of infection,” said Dennis Nash, a professor of epidemiology at the City University of New York.

So, as human exposure to the virus increases, will the virus move into a seasonal pattern? Some believe this trend is already emerging. Hunter points out that the summer surge in cases, hospitalizations, and deaths has been much more mild than in December and January. In the United States, The death toll from COVID-19 is 327. The week of June 15th there were 2,578 cases and the week of Jan. 13th there were 2,578 cases.

“We may never reach the level of herd immunity against SARS-CoV-2 that would reduce summer infection numbers to zero, and it may take another year or two to get there,” said Andy Pecos, a professor of molecular microbiology and immunology at Johns Hopkins University.

But Nash noted that humans have been coexisting with, and exposed to, influenza and other common viruses for hundreds of years, and he predicts that this process could take decades or longer.

If COVID-19 finds a stable seasonal pattern, the question arises as to where its annual peak falls in relation to respiratory syncytial virus, which peaks in early fall, or seasonal influenza, which peaks in mid-winter. Pecos explains the concept of “viral interference,” which means that over time pathogens evolve into cycles that prevent too many viruses from circulating at the same time. “That’s because the first virus infects people and causes a period of nonspecific immunity to other viruses,” he says.

These are all questions that could still take years or decades to properly answer, but coronaviruses’ natural tendency to continue circulating in warmer climates has some scientists suspicious that COVID-19 may not disappear entirely over the summer.

“We’ve known for some time that human coronaviruses are not as seasonal as influenza, and this is certainly due in part to cold and dry weather,” says Harvard epidemiologist Bill Hanage. “In fact, before 2020, coronavirus infections were referred to as summer colds because of their clear bias toward colder months, so this is not surprising.”

Whatever happens, for now, with COVID-19 having a consistent impact year-round, experts feel there needs to be more public health messaging to ensure the most vulnerable are fully vaccinated and have access to needed antiviral medications year-round.

“Any public health professional who is really paying attention would not be making predictions about seasonality of COVID-19 at this point,” Nash said. “If their messaging is accurate, they would be telling people to stay informed all year round, not just in the fall and winter.”

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