Coronavirus News: Researchers Say That COVID-19 Will Ultimately Become A Seasonal Virus But Not Until Herd Immunity Is Achieved
: Middle-east researchers from the American University of Beirut-Lebanon and Qatar University-Doha say that the SARS-CoV-2 coronavirus that caused the COVID-019 disease will ultimately become a seasonal virus just like influenza but not just yet. It only till a global herd immunity is achieved that will this happen.
Their review was published in the journal: Frontiers in Public Health https://www.frontiersin.org/articles/10.3389/fpubh.2020.567184/full
The (RO) or basic reproduction number is the number of secondary cases resulting from a primary case in a susceptible population and is an important indicator to predict the spread of a virus. For a virus to follow a seasonal pattern, and thus wane in summer, its effective R0 should drop below 1.
Currently for SARS-CoV, the R0 is estimated between 2 and 3 and in some estimates as high as 5.7. Several factors in the summer might reduce the effective R0 of respiratory viruses including the effect of warm temperatures and humidity on the stability of the virus and susceptibility of the host as well as behavior of the population such as indoor crowding.
For seasonal influenza virus, its R0 is estimated to be 1.27. Therefore, these aforementioned factors could easily drop the effective R0 to below 1 in summer halting the virus spread and resulting in the observed seasonal pattern of flu. The warm temperatures and humidity of the summer might impact the host immune response and thus its susceptibility to infection by SARS-CoV-2 similar to its effect on influenza .
However, other factors including: (1) a much higher R0, (2) higher stability of SARS-CoV-2 (it can survive for up to 72 h on hard surfaces at temperatures between 21 and 23°C and in relative humidity of 40%), and (3) a largely immunologically naïve population against SARS-CoV-2 compared to influenza make it unlikely for the R0 to drop in summer enough to halt the spread of SARS-CoV-2.
Therefore, without public health interventions, SARS-CoV-2 will continue to spread in summer as witnessed in many countries around the world.
Nonetheless, as the population herd immunity is attained through natural infections and/or vaccinations then the effective R0 is expected to drop substantially making the virus more prone to seasonal fluctuations.
The health researcher suggests that COVID-19, the illness caused by the SARS-CoV-2 virus, will likely follow suit and become seasonal in countries with temperate climates, but only when herd immunity is attained. Until that time, COVID-19 will continue to circulate across the seasons. These conclusions highlight the absolute importance of public health measures needed just now to control the virus.
Dr Hassan Zaraket, of the American University of Beirut in Lebanon who is the senior author of the study warns that "COVID-19 is here to stay and it will continue to cause outbreaks year-round until herd immunity is achieved.
Hence, the public will need to learn to live with it and continue practicing the best prevention measures, including wearing of masks, physical distancing, hand hygiene and avoidance of gatherings.
Along with collaborating author Dr Hadi Yassine, of Qatar University in Doha, the study teams affirms and states that there could be multiple waves of COVID-19 before herd immunity is achieved.
To date it is known that many respiratory viruses follow seasonal patterns, especially in temperate regions. For instance, influenza and several types of coronaviruses that cause common cold are known to peak in winter in temperate regions but circulate year-round in tropical regions. The authors reviewed these seasonal viruses, examining the viral and host factors that control their seasonality as well as the latest knowledge on the stability and transmission of SARS-CoV-2.
The study team explained that coronavirus survival in the air and on surfaces, individual's susceptibility to infections and human behaviors, such as indoor crowding, differ across the seasons due to changes in temperature and humidity. These factors influence transmission of respiratory viruses at different times of the year.
But they warned that in comparison to other respiratory viruses such as the flu, COVID-19 has a higher rate of transmission (R0), at least partly due to circulation in a largely immunologically naïve population.
Hence this implies that unlike the flu and other respiratory viruses, the factors governing seasonality of viruses cannot yet halt the spread of COVID-19 in the summer months. But, once herd immunity is attained through natural infections and vaccinations, the R0 should drop substantially, making the virus more susceptible to seasonal factors.
So far such seasonality has been reported for other coronaviruses, including those that emerged more recently such as NL63 and HKU1, which follow the same circulation pattern like influenza.
Dr Zaraket added, "This remains a novel virus and despite the fast-growing body of science about it there are still things that are unknown. Whether our predictions hold true or not remains to be seen in the future. But we think it's highly likely, given what we know so far, COVID-19 will eventually become seasonal, like other coronaviruses."
Dr Yassine further states that "the highest global COVID-19 infection rate per capita was recorded in the Gulf states, regardless of the hot summer season. Although this is majorly attributed to the rapid virus spread in closed communities, it affirms the need for rigorous control measures to limit virus spread, until herd immunity is achieved".
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