Monday, November 29, 2021

Is COVID-19 here to stay? A team of biologists explains what it means for a virus to be endemic

Now that children ages 5 to 11 are eligible for COVID-19 vaccination and the number of fully vaccinated Americans is increasing, many people may be wondering what the endgame is for COVID-19.

At the start of the pandemic, it was not unreasonable to expect that SARS-CoV-2 (the virus that causes COVID-19) might go away, as historically some pandemic viruses have simply disappeared.

For example, SARS-CoV, the coronavirus responsible for the first SARS epidemic in 2003, spread to 29 countries and territories, infecting more than 8,000 people from November 2002 to July 2003. But thanks to prompt and effective public health interventions, SARS-CoV hasn’t been seen in humans in nearly 20 years and is now considered extinct.

On the other hand, pandemic viruses can also settle slowly at a relatively constant rate of occurrence, maintaining a constant pool of infected hosts that are capable of spreading the virus to others. These viruses are called “endemic”.

Examples of viruses endemic to the United States include those that cause the common cold and the seasonal flu that appear year after year. Much of this, the virus that causes COVID-19, is unlikely to die out, and most experts now expect it to become endemic.

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

What determines which viruses become endemic?

So why did the first SARS virus become extinct since 2003 (SARS-CoV), while it (SARS-CoV-2) may be 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 really well from person to person, may never die on their own because they are so good at infecting new people. .

When a virus first enters an unimmunized population, its infectivity is defined by scientists using a simple mathematical term called R0, pronounced “R-naught”. It is also called reproduction number. The reproduction number of a virus represents how many people are infected on average by each infected person. For example, the first SARS-CoV had an R0 of about 2, which means that each infected person transmits the virus to an average of two people. For the delta variant strain of SARS-CoV-2, R0 is between 6 and 7.

Public health officials aim to slow the rate at which the virus spreads. 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, it took little public health intervention to drive the virus to extinction. Given the highly transmissible nature of the delta variant, the challenge of eliminating the virus will be enormous, meaning the virus is more likely to be endemic.

In August 2020, approximately 500,000 motorcyclists took to the streets of Sturgis, South Dakota, at the city’s annual motorcycle rally. Masks were encouraged but not required. COVID-19 cases increased across the state.
Brian R. Smith / AFP via Getty Images

Is COVID-19 ever going away?

It is clear that SARS-CoV-2 is very successful in infecting new people, 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 is so easily passed from person to person, and how human behavior plays a role in that virus transmission.

SARS-CoV-2 is a respiratory virus that spreads through the air and is efficiently transmitted when people congregate. Important public health interventions, such as the use of masks and social distancing, have been instrumental in slowing the spread of the disease. However, any lapse in these public health measures can have dire consequences. For example, the 2020 motorcycle rally brought together nearly 500,000 people in Sturgis, South Dakota, during the early stages of the pandemic. Most of the attendees were masked and not following social distancing. That incident was directly responsible for the increase in COVID-19 cases in the state of South Dakota and across the country. This shows how easily the virus can spread when people are careless in their defense.

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The virus that causes COVID-19 is often associated with superspreading events, in which several 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 that is spreading in a community. These vital “supercarriers” have a disproportionately large impact on infecting others, and will continue to perpetuate epidemics if they are not tracked before spreading the virus to the next person. We do not currently have a nationwide screening program to identify these individuals.

Finally, asymptomatic infected people account for about half of all infections with COVID-19. This, when combined with the wide range of times in which people can be contagious – up to two days before and 10 days after symptoms appear – provides many opportunities for virus transmission, as do people who do not know they are sick. , usually take some measures to differentiate it from others.

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

An elderly woman wearing a mask gets a shot.
An elderly woman receives a Pfizer COVID-19 booster shot at a clinic in San Rafael, California.
Justin Sullivan/Getty Images News via Getty Images

What will our future with COVID-19 look like?

Given the considerations discussed above and what we know about COVID-19 so far, many scientists believe that the virus that causes COVID-19 will settle into endemic patterns of transmission. But our inability to eliminate the virus does not mean that all hope is lost.

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

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

With global virus surveillance and the speed at which safe and effective vaccines are developed, we are well prepared to tackle the ever-evolving target of SARS-CoV-2. Influenza is endemic and develops quickly, but seasonal vaccination enables life to proceed normally. We can expect the same for SARS-CoV-2 – after all.

How do we know if and when SARS-CoV-2 became endemic?

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

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Once the rates of SARS-CoV-2 stabilize, we can call it endemic. But depending on where you are in the world, this transition can look different. For example, countries with high vaccine coverage and plentiful boosters could soon settle into predictable spikes of COVID-19 during the winter months, when environmental conditions are more conducive to virus transmission. Conversely, unpredictable epidemics may persist in areas with low vaccination rates.

This article is republished from – The Conversation – Read the – original article.

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