COVID-19: From pandemic to endemic

On March 11, 2020, the World Health Organization declared that the COVID-19 outbreak that had begun just a few months earlier in Wuhan, China, was a global pandemic. A pandemic is defined as “an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.” More significantly, however, the immediate experience of a pandemic triggered by a novel pathogen like SARS-CoV-2 is often a public health emergency that requires population-wide efforts to mitigate disease and death. This certainly was the global experience of the COVID-19 pandemic, which led to lockdowns of varying intensities in the countries of the world.

Pandemics are often public health emergencies for one or two reasons. First, they are emergencies because they can be associated with high hospitalization rates. Thus, the scale of transmission can overwhelm the health care infrastructure of a society, indirectly leading to an increase in deaths from causes that could have been treated in a hospital. Second, pandemics are public health emergencies because they can be associated with high mortality rates. The pathogen simply kills many people. As we experienced with the COVID-19 pandemic, both scenarios are not mutually exclusive: SARS-CoV-2 increased both hospitalization rates and death rates around the world.

How does a pandemic end? In one of two ways. First, the novel pathogen could simply be eradicated. This can happen if the pathogen is easily detectable and controllable. Second, the novel pathogen can be tamed. This happens when the pathogen evolves such that it leads to lower hospitalization rates and/or fewer deaths. At this point in time, it appears that the COVID-19 pandemic is moving down the second path. It is moving from a pandemic to an endemic. This transition began with the appearance of Omicron variant in Q4 2021.

The passing of Omicron variant in January 2022 has given the Philippines a period of respite. Unlike many of our neighbors in East Asia, like Japan and South Africa, our daily case numbers, both in NCR and nationwide, though increasing slowly from the BA.5 variant, are still relatively low. How do we explain the current period of calm? Simply, the Filipino people are enjoying the protection of significant hybrid immunity from both Delta and Omicron surges, and the success of our ongoing national vaccination campaign, especially in our highly urbanized areas. Hybrid immunity is the population immunity we see in a society that has experienced both high numbers of previous infections and high vaccination rates.

Here in the Philippines, our Omicron surge was the largest COVID-19 wave that we have experienced, so far. However, our official numbers were not as dramatic as those being reported in South Korea or Vietnam because we had significant natural immunity from the Delta, and maybe Beta, surges, and we were not testing as much as our neighbors. Nonetheless, back-of-the-envelope calculations that I have performed using the COVID-19 testing numbers published by the Department of Transportation suggest that up to half of the Metro Manila population were infected by Omicron variant.

What does this mean going forward? We have to continue to vaccinate and to booster our people to prolong the hybrid immunity that we possess at this time. Our current population immunity is waning gradually—it is slowly disappearing—which is why we are seeing the gradual increase in cases over the past several months. However, this should not be a cause of grave concern. Though antibody-mediated immunity wanes quickly—the missiles of our body’s army—cell-mediated immunity—the tanks of our body’s army—is more robust. These cellular tanks should give our Filipino people enough immunity to prevent severe disease and death from COVID-19. Nonetheless, it will be important to continue boosting our senior citizens and other vulnerable kababayans to help them be as protected as possible going forward.

For now, we have to continue to prepare for this endemic stage of the pandemic. We need to train our health care workers to triage COVID-19 positive patients so that most of them will remain at home to recover from their Omicron illness. We need to build stockpiles of antivirals that can help our more vulnerable neighbors who get sick to fight off the infection in their homes. And we have to strengthen our health care infrastructure to be able to withstand future COVID-19 seasons when numbers ebb and flow. We have to establish health care teams and clinics that can treat our fellow citizens who will suffer from long COVID, which is a general term used to describe the range of ongoing health problems people can have after their initial infection.

A question I get all the time: When will COVID-19 become an endemic? Is it only about numbers? No. Endemicity is not merely a medical or biological phenomenon. In fact, in my view, it is primarily a sociological one. COVID-19 will become endemic once it does not threaten the health care infrastructure of our country. With endemic COVID-19, Filipinos will still get COVID-19, some of them will be hospitalized, and tragically, a few will still die. However, if most of them survive and most of them recover at home, then it will cease to be the public health emergency that is at the heart of a pandemic.

Finally, I should note there are global scientific experts who have suggested COVID-19 will become endemic when sufficient numbers of people in a population have been infected with COVID-19 a handful of times. This claim emerges from the observation that naturally acquired immunity appears to be more long-lasting than vaccine-induced immunity which decays faster. They propose that our COVID-19 vaccinations have now protected our societies enough that we should not be overly concerned with the ongoing transmission of mild variants since these mild cases will, in fact, accelerate the transition to endemic COVID-19.

In sum, we thank God for the relative calm that we are experiencing at this time in the pandemic. We do not need to be afraid of COVID-19. The emergence of Omicron variant has made the transition to endemic disease much more likely. We have to work together to accelerate this transition.

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Rev. Fr. Nicanor Austriaco, O.P., Ph.D., S.Th.D. is a molecular biologist and professor at the University of Santo Tomas. He was a member of Task Force T3 (Test, Trace, Treat).

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