What is endemic? The disease is endemic when it is a continuous presence in a population. Endemic diseases follow predictable patterns and happen at a baseline level. According to WHO, malaria is endemic in several parts of the world, with approximately 229 million cases recorded in 2019. Seasonal flu in the US is another type of endemic disease. Could Covid-19 eventually become an endemic disease like flu and malaria?
Professor Yonatan Grad answers critical questions on COVID-19 becoming an endemic disease. He is an associate professor of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health.
What is endemic? What is the potential timeline for COVID-19 to become endemic?
The hope that COVID-19 will become endemic means that the pandemic will not end with the virus dying. Instead, the more optimistic view is that enough people will gain immunity from vaccination and natural infection. Professor Grad said there would be less transmission and less hospitalization and death due to COVID-19, even if the virus is still present.
The expected continued pattern of SARS-CoV-2 is different from the first round of SARS in 2003. It’s also different from the Ebola virus outbreak in West Africa in 2014 when public health measures finally prevented it. This comparison highlights the critical need to improve public health infrastructure and surveillance systems. Such enhancements would help monitor and respond to the next potential pandemic virus.
Professor Grad also said that it is difficult to expect what the timeline would be and the anticipated COVID-19 to endemicity. It is still dependent on strength and duration immunity from vaccination and natural infection. It also depends on the patterns of social contact and the level of transmissibility of the SARS-Cov-2.
Professor Grad further emphasized the answer to the question “what is endemic. The tendency towards endemicity will likely differ with other diseases, given the varied responses to COVID-19 across the globe. Some places are engaging in “zero-COVID” policies, others with limited interventions, and others with limited vaccination capacity.
What the past events tell us about how viruses like COVID-19 can become manageable threats?
A few respiratory viruses introduced to the human population spread across the world and shifted to endemic patterns. These days, the most common example is the 1918 flu pandemic caused by an A/H1N1 influenza virus. There are other outbreaks of influenza that includes the following:
- Flu pandemic in 1957 caused by an A/H2N2 influenza virus
- Flu pandemic in 1968 due to A/H3N2 influenza virus
- Swine flu outbreak in 2009 from an A/H1N1 influenza virus
The pandemics usually began with higher infection fatality rates as the viruses continued to circulate. Although decreasing fatality rates after pandemics may be due to several factors, one possible factor is that the initial round of exposure to a pathogen protects against reinfection. Likewise, the severity of the disease may be lower if reinfection occurs. Vaccines also confer protection, as shown by the data from the COVID-19 vaccines.
What is the possibility that we will need booster shots every year?
Professor Grad said that the need for booster shots is not clear as significant biology and policy issues are yet to be answered. In terms of biology, the extent of antigenic evolution in SARS-CoV2 remains to be discovered. In addition, the period of immune protection from vaccination and the likelihood of reducing infection still needs confirmation from experts.
On the policy side, what burden of disease are we prepared to tolerate in a population? This policy question is not only about COVID-19 and should remind health experts and policymakers to re-evaluate the response to other preventable diseases.
Previous pandemics have prompted significant changes in the way we live, and we have come to accept them as usual. For instance, installing screens on our doors and windows protects us from mosquitoes that cause yellow fever and malaria. Professor Grad concluded that the lessons learned from COVID-19 in disease prevention could also bring similar long-term improvements in the future.
