Covid-19 may become seasonal when herd immunity is achieved, suggest experts

Covid-19 may become seasonal in countries with temperate climates once herd immunity is achieved according to a new review published in Frontiers in Public Health.

The review suggests that Covid-19 may follow suit similar to other respiratory viruses that follow seasonal patterns 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,” reads an official release.

Senior author of the study Dr Hassan Zaraket, of the American University of Beirut in Lebanon said, "Covid-9 is here to stay and it will continue to cause outbreaks year-round until herd immunity is achieved. Therefore, the public will need to learn to live with it and continue practising the best prevention measures, including wearing of masks, physical distancing, hand hygiene and avoidance of gatherings."

Collaborating author Dr Hadi Yassine, of Qatar University in Doha, affirmed that there could be multiple waves of the infection before herd immunity is achieved.

The authors reviewed 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 virus that has caused the pandemic.

The researchers explored how the virus survives in the air and on surfaces along with people's susceptibility to infections and human behaviours, such as indoor crowding. These factors differ across the seasons due to changes in temperature and humidity and influence the transmission of such respiratory viruses at different times of the year.

However, the rate of transmission in terms of the novel coronavirus is much higher as compared to respiratory viruses such as the flu. This is partly due to the circulation of the virus in a largely immunologically naïve population. This means that these factors cannot halt the spread of the virus in the summer months.

However, once herd immunity is achieved through natural infections and vaccinations, the rate of infection may drop significantly with the virus likely to follow seasonal patterns.

“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,” read the release.

"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," said Zaraket.

Dr Yassine said, "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".