Is COVID-19 Here To Stay? Biologists Explain What It Means for a Virus To Become Endemic

The best way to stop an infectious virus like COVID-19 is through a global vaccination program.

With children ages 5 to 11 eligible for COVID-19 vaccination and the number of fully vaccinated people in the US on the rise, many people may be wondering what the end game is for COVID-19.

In the beginning of the pandemic, it was not unreasonable to expect that SARS-CoV-2 (the virus that causes COVID-19) could simply disappear, as historically some pandemic viruses have simply disappeared.

For example, SARS-CoV, the coronavirus responsible for the first SARS pandemic in 2003, spread to 29 countries and regions and infected more than 8,000 people from November 2002 to July 2003. But thanks to rapid and effective interventions in Public health, SARS-CoV has not been observed in humans for nearly 20 years and is now considered extinct.

On the other hand, pandemic viruses can also gradually establish themselves at a relatively stable rate, maintaining a constant pool of infected hosts that can spread the virus to others. These viruses are said to be ‘endemic’.

Examples of endemic viruses in the United States are viruses that cause the common cold and seasonal flu that appear year after year. Much like this one, the virus that causes COVID-19 is unlikely to become extinct, and most experts now expect it to become endemic.

We are a team of virologists and immunologists from the University of Colorado Boulder who study animal viruses that infect humans. An essential focus of our research is to identify and describe the key adaptations that animal viruses need to persist in the human population.

Influenza and the four human coronaviruses that cause the common cold are endemic; they are highly contagious and evolve quickly.

What determines which viruses become endemic?

So why did the first SARS virus from 2003 (SARS-CoV) become extinct when this (SARS-CoV-2) may become endemic?

The ultimate fate of a virus depends on how well it maintains its transmission. In general, viruses that are highly contagious, meaning they spread very well from one person to another, will never die out on their own because they are so good at finding new people to infect.

When a virus first invades a population without immunity, its infectivity is defined by scientists using a simple mathematical term called R0, which is pronounced “R-naught”. This is also known as the reproduction number. The reproduction number of a virus indicates how many people are infected by each infected person on average. For example, the first SARS-CoV had an R0 of about 2, meaning that each infected person passes the virus to two people on average. For the delta variant strain of SARS-CoV-2, the R0 is between 6 and 7.

The goal of public health authorities is to slow the rate at which viruses spread. Universal masking, social distancing, contact tracing and quarantine are all effective tools to reduce the spread of respiratory viruses. Since SARS-CoV was poorly transmissible, only a small amount of public health intervention was needed to eradicate the virus. Given the highly transmissible nature of the delta variant, the challenge to eliminate the virus will be much greater, meaning the virus will become endemic sooner.

Will COVID-19 Ever Go Away?

It is clear that SARS-CoV-2 is very successful in finding new people to infect, and that people can become infected after vaccination. For these reasons, the transmission of this virus is not expected to end. It is important that we consider why SARS-CoV-2 passes so easily from one person to another and how human behavior plays a role in that virus transmission.

SARS-CoV-2 is a respiratory virus that is airborne and efficiently transmitted when people come together. Critical public health interventions, such as the use of masks and social distancing, have been instrumental in slowing the spread of disease. However, any deviation from these public health measures could have serious consequences. For example, a 2020 motorcycle rally brought together nearly 500,000 people in Sturgis, South Dakota, during the early stages of the pandemic. Most of those present were unmasked and did not observe social distancing. That event was directly responsible for an increase in COVID-19 cases in the state of South Dakota and across the country. This shows how easily the virus can spread if people are not wary.

In August 2020, approximately 500,000 motorcyclists rode the streets of Sturgis, South Dakota, during the city’s annual motorcycle rally. Masks were encouraged, but not required. COVID-19 cases across the state increased. (stock photo)

The virus that causes COVID-19 is often associated with superspreading events, in which many people are infected at once, usually by one infected person. In fact, our own work has shown that only 2% of people infected with COVID-19 carry 90% of the virus circulating in a community. These important “supercarriers” have a disproportionate impact on infecting others, and if they are not detected before spreading the virus to the next person, they will continue to perpetuate the epidemic. We currently do not have a nationwide screening program to identify these individuals.

Finally, asymptomatically infected people account for about half of all COVID-19 infections. This, coupled with a wide range of time in which people can be contagious – two days before and 10 days after symptoms appear – offers many opportunities for virus transmission, as people who don’t know they are sick generally take few steps to prevent them. to isolate from others.

The contagious nature of SARS-CoV-2 and our highly interconnected society form a perfect storm that is likely to contribute to continued spread of the virus.

Booster shots will likely be required to maximize vaccine-induced protection against infection.

What does our future look like with COVID-19?

Given the considerations discussed above and what we know so far about COVID-19, many scientists believe that the virus that causes COVID-19 is likely to establish itself in endemic transmission patterns. But our inability to eradicate the virus does not mean that all hope is lost.

Our post-pandemic future will depend heavily on how the virus evolves in the coming years. SARS-CoV-2 is a completely new human virus that is still adapting to its new host. Over time, we can see the virus become less pathogenic, similar to the four coronaviruses that cause the common cold, which are little more than a seasonal nuisance.

Global vaccination programs will have the greatest impact in reducing new cases of the disease. However, the SARS-CoV-2 vaccine campaign has so far reached only a small percentage of the people on the planet. In addition, breakthrough infections in vaccinated people still occur because no vaccine is 100% effective. This means that booster shots will likely be required to maximize vaccine-induced protection against infection.

With virus surveillance worldwide and the speed with which safe and effective vaccines have been developed, we are well placed to tackle the ever-evolving target, SARS-CoV-2. Flu is endemic and evolving rapidly, but seasonal vaccination allows life to continue. We can expect the same for SARS-CoV-2 — eventually.

How will we know if and when SARS-CoV-2 becomes endemic?

Four seasonal coronaviruses are already circulating endemic to humans. They tend to recur annually, usually during the winter months, and are more common in children than adults. The virus that causes COVID-19 has not yet settled into these predictable patterns and is instead flaring up unpredictably around the world in ways that are sometimes difficult to predict.

Once the percentages of SARS-CoV-2 stabilize, we can call it endemic. But this transition may look different based on where you are in the world. For example, countries with high vaccination coverage and abundant boosters can quickly settle into predictable peaks of COVID-19 during the winter months, when environmental conditions are more favorable for virus transmission. In contrast, unpredictable epidemics can persist in regions with lower vaccination coverage.

Written by:

Sara Sawyer, professor of molecular, cellular, and developmental biology, University of Colorado Boulder Arturo Barbachano-Guerrero, postdoctoral researcher in virology, University of Colorado Boulder Cody Warren, postdoctoral researcher in virology and immunology, University of Colorado Boulder

This article was first published in The Conversation.