8/13/2023 0 Comments Virus spike definition![]() ![]() Some of this increase may be driven by more widespread testing now. Different waves can have different features, too, regarding factors like disease severity or which populations are most affected. Insight from the past suggests that discrete waves result as a disease spreads into and out of a population. A study of H1N1 influenza in 2009-2010 found that the second wave affected more older people, with underlying conditions. More recently, the 2009 H1N1 influenza pandemic, though mild, had two distinct waves this virus still commonly shows up in seasonal influenza outbreaks. ![]() It’s unclear whether being infected earlier on protected individuals during later waves. The proportion of influenza patients who were severely ill or died was much higher in the last two waves compared to the first. The current COVID-19 pandemic is often compared to the 1918 H1N1 influenza pandemic, which had three distinct waves over the course of a year. 1918 Influenza: the Mother of All Pandemics. The waves were broadly the same globally during the pandemic. ![]() Three waves of death: weekly combined influenza and pneumonia mortality, United Kingdom, 1918–1919. The second wave was much more severe, particularly in younger adults. For example, the 1889-92 influenza outbreak had three distinct waves, which differed in their virulence. University of Oxford scholars of evidence-based medicine Tom Jefferson and Carl Heneghan have summarized past waves in respiratory virus pandemics over the previous 150 years. Some of the current talk of coronavirus waves likely stems from comparisons with past epidemics that did show these peaks and troughs of infections. Ebb and flow, 150 years of influenza waves is nowhere near what epidemiologists call herd immunity in the general population, however mathematical modelers suggest at least between 43% and 60% of people would need to be immune to SARS-CoV-2 for that to be the case. As more individuals become immune to a pathogen, its spread slows and eventually stops as the virus runs out of new people to infect. Waves and seasonal dynamics are also affected by levels of immunity in the human population. Some scientists model that SARS-CoV-2 will eventually become seasonal like other coronaviruses. But recent outbreaks in Florida, Arizona, Texas and Southern California suggest that warm or humid weather is not sufficient to stop the spread of the disease. It’s possible that SARS-CoV-2, the coronavirus that causes COVID-19, spreads more efficiently under certain weather conditions. Annual epidemics, like of influenza may occur because of climate or patterns of social mixing – often driven by the school year or people staying inside more during the winter. Some pathogens may spread less well with greater humidity. Several factors influence whether a particular disease is seasonal in nature. Seasonal coronaviruses, like 229E or HKU1, which cause the common cold, have a high point from around December through March, according to research in the U.S. Some diseases come in somewhat predictable seasonal waves, with higher transmission rates at some times of the year than at others. Historical outbreaks of infectious diseases offer some models for how the course of a disease like COVID-19 might unfold over time. The word “wave” implies a natural pattern of peaks and valleys it hints that even during a lull, future outbreaks of disease are possible. ![]() A wave implies a rising number of sick individuals, a defined peak, and then a decline. There’s no strict definition for what is or is not an epidemic wave or phase. But looking to the history of previous epidemics and other countries’ current COVID-19 outbreaks can be useful. As an epidemiologist, I know that disease waves aren’t scientifically defined. Talking about waves of disease, with the implication of predictable rises and falls, is part of that. Six months into the pandemic, people are looking for ways to make sense of what’s happening. stuck in a first wave? Through the worst of it? Headed for a second round? Have the weeks and months of lockdown really helped? What do the trends in diagnoses and deaths mean for the course of the pandemic? Is the U.S. is still firmly within a first wave of cases.Īs media broadcast information about daily increases in the number of cases, it’s hard not to wonder which way the country is headed. On the other hand, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, warns that the U.S. Panic about a second wave of coronavirus cases is “ overblown,” Vice President Mike Pence wrote in June, implying the U.S. ![]()
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