Why is COVID-19 likely to become an endemic disease, like the flu?

With COVID-19 vaccination programmes in various stages of progress across the world, many people are asking, 'How much longer will the pandemic last, and how long will we need to adhere to preventive measures aimed at curbing the spread of disease?'

1. "It's important to consider the stage of each country's vaccination programme in answering this question," says Dr Noluthando Nematswerani, head of the centre for clinical excellence at Discovery Health.
2. "In South Africa, our vaccine programme is still in a relatively early phase. At the start of July 2021 (at the time of writing) approximately 3.5 million vaccines have been administered. Our aim is to vaccinate approximately 40 million adult South African residents in total through all three phases of the local rollout.
3. "For now, we do not have high enough levels of immunity in the broader population - and particularly in high-risk population groups - to relax the preventive measures we are practising. As much we may all long to return to our pre-COVID-19 freedoms, we must continue practising the measures that protect us from contracting covid-19 - even after we receive our first or full vaccine dose and are considered fully vaccinated."

People are considered fully vaccinated two weeks after their second dose of the Pfizer vaccine or 28 days after the single-dose Johnson & Johnson vaccine.

• Read more on Pfizer-BioNTech COVID-19 overview and safety
• Read more on Johnson & Johnson's Janssen COVID-19 overview and safety

There are two ways of acquiring some immunity to COVID-19. Either way, the risk of infection remains

"The US Centers for Disease Control and Prevention's (CDC) 17 June update advises that COVID-19 vaccines reduce the risk of people spreading COVID-19. However, we don't fully understand how well they do this. For now, we know that being vaccinated does not guarantee that we will not contract COVID-19. What it does mean is that we are far less likely to experience severe COVID-19 illness."

"The first way of acquiring immunity to COVID-19 disease is through natural immunity after contracting COVID-19 and recovering. This comes at a price as people can develop severe illness and lose their lives, or recover from mild or severe COVID-19 but some may still face the symptoms of long COVID for weeks or months to come," says Dr Nematswerani.

"The second way is to be vaccinated against COVID-19. In this way you acquire immunity through a vaccine that mimics infection, stimulates an immune response to heighten immunity to further infection."

"Both natural and vaccine-acquired COVID-19 immunity do not offer full protection against infection. That means even after we've recovered from or been vaccinated against COVID-19, we can still contract and spread the disease. We are seeing 'breakthrough infections' or new COVID-19 cases in people who are fully vaccinated against the disease. Those people are symptomatic and can still pass on the virus."

"We must also bear the emergence of new viral variants in mind. South Africa's second wave of infection was driven by the beta variant. Our third wave of infection has been driven by the delta variant. Those COVID-19 variants that prove highly transmissible have the potential to evade immunity levels, and it takes time to establish the extent to which is this possible."

As the pandemic progresses, what are we learning about the likelihood of reaching population immunity? Why has the thinking begun to shift?

We've heard that we need to reach so-called 'population immunity' to make a marked impact on rates of infection and overcome the pandemic. Population immunity has been predicted as occurring when around 70% or as high at 90-95% (in the presence of emerging variants) of the population gains immunity to the virus that causes COVID-19 - either through vaccination or through exposure to the virus.

• It's important to understand what we mean by population immunity

Dr Nematswerani explains: "When a sufficiently significant number of people have been vaccinated against a disease, we reach a state where an infected person is very unlikely to transmit an illness to others as they have a high level of immunity or resistance to infection. In this way you eventually overcome the infection and prevent it from spreading in communities almost altogether."

"We have reached this end in the case of other diseases where vaccinations have been very effective in eradicating infection from communities entirely. Measles, mumps, polio, and chickenpox are examples of infectious diseases that were once very common but are now rare as vaccines have assisted us to reach population immunity, virtually eradicating transmission. This means that we are all either directly (vaccinated people) or indirectly (unvaccinated people) protected against an infectious disease due to levels of population immunity high enough to curb transmission outright."

• Here's the difference between these sorts of diseases and others like the flu or COVID-19

"In the case of measles, mumps, polio, or chickenpox there is very little change in the viruses that cause the diseases over time. In contrast, viruses like SARS-CoV-2 (the virus that causes COVID-19) and the influenza (flu) virus, mutate on an ongoing basis as they infect us and make copies of themselves in our bodies to spread. Keep in mind that these mutations are random, and may make the virus less effective than the previous strain was."

• Understand how the COVID-19 virus works and how viral variants develop.

"However, these mutations can also result in beneficial changes that make the virus more transmissible or more serious. In the case of the COVID-19 virus we have seen alpha, beta, gamma and delta variants emerge so far and we know that the beta and delta variants have spread faster than precious COVID-19 viral strains. In the case of the influenza (or flu) virus, ongoing mutations and the resultant variants are the reason we require annual flu vaccines to give us protection against the latest viral strains in circulation. Like the COVID-19 vaccine, the flu vaccine does not prevent us getting flu. Rather, it lowers our chances of severe flu, which is especially important in the case of people at high risk of serious illness or death from the flu - such as pregnant women, people who are immunocompromised or who live with chronic illnesses, or the elderly."

• That's why it's unlikely that we will ever eradicate COVID-19 entirely

"The current pandemic factors which include the rapid emergence of variants of concern of the COVID-19 virus and vaccine uptake are some of the reasons that make it unlikely to reach population immunity in the case of this disease," explains Dr Nematswerani. "We will ongoingly be challenged by new variants capable of evading the immunity levels in local and global society. This is why we are very likely to need possibly annual COVID-19 vaccine booster shots, just as we have annual flu vaccines to 'update' our immunity."

"We speak about endemic infections, where a disease becomes a norm within a population and where we live with but people no longer die of the disease. COVID-19 is likely to become endemic."

• Right now, there is a move towards 'containment' rather than 'population immunity' and reaching the point at which people no longer die of COVID-19 infection

"All in all this means that COVID-19 infections are likely to endure in the way the flu infections do. And we will still need to wear our masks and take other preventive measures until a sufficient portion of the population is vaccinated so as to prevent severe illness and death when people do contract COVID-19."

"It is currently unclear when South Africa will reach the point of sufficiently high population immunity and adequate containment of COVID-19 to allow for relaxation of preventive measures, but it is hoped that we will be well on our way to our target of vaccinating close to 40 million adults by the end of 2021."

Let's keep our focus on saving lives and livelihoods through a successful vaccine rollout

In the United States of America fully vaccinated people are able to resume pre-pandemic activities. This means that people who have been vaccinated do not need to quarantine when exposed to COVID-19 or adhere to mask wearing or social distancing.

"However, we must remember that this is because close to 160 million people in the United States of America have received a vaccine (at 1 July 2021) and 46.7% of the population is fully vaccinated (have had both doses of a two-dose vaccine)," adds Dr Nematswerani.

"I am confident that South Africa will get there in time. It's critical that we make a success of our national vaccine rollout as this is a fundamental pillar in our approach to protecting both lives and livelihoods in our country. Furthermore, as Dr Ryan Noach points out in a recent LinkedIn column, the speed of our vaccine rollout is central to our recovery as a country on multiple levels."