Why Covid-19 is Spreading This Summer

9 August 2024 By Johnber  

NewsTogether

 Covid-19 does not adhere to normal seasonal patterns like other respiratory viruses. Every July for the past four years, epidemiologists at the US Centers for Disease Control and Prevention (CDC) have noted a significant rise in Covid-19 cases and hospitalizations, a trend now known as the "summertime surge." This summer, the US is seeing particularly high Covid-19 rates in Arizona, California, Hawaii, and Nevada, with positive tests reaching 15.6% in the first week of July.

 Across the Atlantic, the UK's Health Security Agency reports a similar trend, with positive Covid-19 tests increasing from 4% at the end of March to 14% by the end of June. This rise is attributed to the FLiRT subvariants, the latest evolution of the Omicron strain of Covid-19. These subvariants have developed mutations in the spike protein, enabling them to evade neutralizing antibodies while still binding effectively to the ACE2 receptor on human cells.

 Shan-Lu Liu, director of the Viruses and Emerging Pathogens Program at The Ohio State University, explains that these subvariants strike a balance between immune evasion and cell binding, driving new cases. The elderly and immunosuppressed are particularly vulnerable and are advised to receive booster shots, including the XBB.1.5 monovalent vaccine targeting the Omicron XBB 1.5 subvariant.

 Understanding these emerging variants is crucial for updating Covid-19 vaccines. Based on the work of Liu and others, US regulators and the World Health Organization have made specific recommendations for new vaccine targets, ready for the autumn rollout. However, predicting when new strains will emerge remains challenging.

 Seasonal patterns in respiratory infections are influenced by the virus itself, the number of susceptible individuals, and conditions conducive to spread. Covid-19's year-round transmission contrasts with the seasonal peaks seen in influenza and Respiratory Syncytial Virus (RSV). Factors such as gatherings at festivals and concerts, and the use of air conditioning, which dries the air and promotes viral spread, exacerbate summer outbreaks.

 In the UK, the recent Euro 2024 football tournament likely contributed to the increase in Covid-19 cases, with peaks around England's matches. Unlike other respiratory viruses, Covid-19's relatively recent emergence means population immunity is lower. Low vaccination rates exacerbate this, with only 22.7% of over-18s in the US up to date on their Covid-19 vaccines as of early July, compared to 48.2% for influenza.

 Experts like Denis Nash from The City University of New York note that fluctuating population immunity, driven by vaccine uptake and recent infections, leads to these seasonal surges. Whether Covid-19 will become a truly seasonal virus remains uncertain. Some believe a trend is emerging, with summer surges being milder than winter ones. In the US, Covid-19 deaths in mid-June were significantly lower than those in mid-January.

 The transition to a seasonal pattern could take years or even decades. Scientists like Andy Pekosz from Johns Hopkins University suggest that achieving stable population immunity against SARS-CoV-2 might take time. If Covid-19 becomes seasonal, it will need to find a place among existing peaks of other viruses like RSV and influenza, which typically peak in early autumn and mid-winter, respectively.

 The concept of "virus interference" means that pathogens evolve cycles to avoid simultaneous circulation, providing a period of nonspecific immunity after an initial infection. As we continue to live with Covid-19, understanding its patterns and adapting public health responses will be crucial.

Keywords

1. epidemiologist: a scientist who studies the spread and control of diseases
   

2. spike: a sharp increase
   

3. subvariant: a variation of a virus that has mutated from the original strain
   

4. mutation: a change in the genetic material of an organism
   

5. spike protein: a structure on the surface of a virus that allows it to enter human cells
   

6. neutralizing antibodies: proteins in the immune system that can neutralize pathogens
   

7. immune system: the body's defense against infectious organisms and other invaders
   

8. receptor: a protein on the surface of a cell that binds to specific molecules
   

9. immunosuppressed: having a weakened immune system
   

10. booster shot: an additional dose of a vaccine
    

11. monovalent: targeting a single strain or component
    

12. respiratory tract: the passageway that includes the nose, throat, and lungs
    

13. vaccine: a substance that stimulates the body's immune response to prevent disease
    

14. regulator: an authority or agency responsible for supervising and enforcing laws and regulations
    

15. seasonality: the tendency for certain events to occur at specific times of the year
    

16. endemic: a disease or condition regularly found among particular people or in a certain area
    

17. transmission: the act of passing something from one person or place to another
    

18. sterilizing immunity: the body's ability to eliminate a pathogen before it can replicate
    

19. immunity: the ability of an organism to resist infection
    

20. virology: the study of viruses
    

21. consultant: an expert who gives professional or technical advice
    

22. microbiology: the study of microorganisms
    

23. immunobiology: the study of the immune system
    

24. pathogen: a bacterium, virus, or other microorganism that can cause disease
    

25. fluctuating: rising and falling irregularly in number or amount
    

26. uptake: the acceptance or adoption of something
    

27. virus interference: the phenomenon where one virus inhibits the replication of another virus
    

28. nonspecific immunity: the general defense mechanisms of the immune system that respond to pathogens in a generic way
    

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