Coronavirus: What will happen to the pandemic in 2021 and beyond?

June 2021. The world has been in a pandemic regime for a year and a half. The virus does not give up and continues to spread at a slow pace; periodic lockdowns have become the new norm. There is an approved vaccine that is effective for six months, but not everyone is able to get it due to the difficulty of negotiating internationally.

An estimated 250 million people have been infected worldwide and 1.75 million have died.

Scenarios like this represent how the COVID-191 pandemic could develop. Around the world, epidemiologists are making short- and long-term projections as a way to prepare for and potentially mitigate the spread and impact of SARS-CoV-2, the virus that causes COVID-19.

While their predictions and timelines vary, the modelers agree on two things: COVID-19 will stay with us for a long time, and the future depends on many unknown factors, including whether people develop long-term immunity to the virus. whether there is seasonality on its distribution and – perhaps most importantly – from actions by governments and individuals.

“The future will depend a lot on how closely social interaction is resumed and what preventive measures we take,” says Joseph Wu, disease modeller at the University of Hong Kong.

Recent models and effective lockdowns suggest that changes in the behavior of most people can reduce the spread of COVID-19. According to Jonathan Grad, an epidemiologist at Harvard School of Public Health. TH Chan in Boston, Massachusetts, restrictions are loosened in many countries, leading some people to assume the pandemic is over. “But that’s not the case. We have a long way to go. “

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But in some cases, the easing of lockdowns brought encouraging news. Early evidence suggests that changes in personal behavior, such as washing hands and wearing masks, that persist after severe restrictions can help stem the wave of infections.

In a June report, a team at Imperial College London’s MRC Center for Global Infectious Disease Analysis found that people’s behavior in terms of masks, hand washing and social distancing had changed significantly.

A team from Anhembi Morumbi University in São Paulo, Brazil, concluded that if 50–65% of people exercise caution in public, then gradually reducing social distancing measures every 80 days could help prevent further peaks in infection over the next two years.

“We need to change the culture of interaction with other people,” the researchers say.

Overall, it is good news that even without testing or a vaccine, behavior can significantly affect disease transmission.

In regions where the spread of COVID-19 is starting to decline, the researchers say the best approach is close surveillance by testing, isolating new cases and tracing their contacts.

The analysis, carried out by the LSHTM Center for Mathematical Modeling of COVID-19 Infectious Diseases Working Group, simulated new outbreaks of varying infectiousness, starting with 5, 20 or 40 reported cases.

The team concluded that contact tracing must be fast and extensive to effectively deal with the outbreak – tracing 80% of contacts within a few days.

At the same time, 80% of contacts can be nearly impossible to track in regions where there are thousands of new infections per week – and worse, the tracking quality is likely to be underreported.

For now, mitigation measures such as social distancing should continue as long as possible to prevent a second major outbreak.

What will happen when it gets colder?

Summer obviously doesn’t stop the virus completely, but warm weather can make it easier to contain it in temperate regions. Experts believe that in regions where it becomes colder in the second half of 2020, the transmission of the virus may increase again.

Many human respiratory viruses – influenza, other human coronaviruses and respiratory syncytial virus (RSV) – follow seasonal fluctuations that lead to winter outbreaks, so it is likely that SARS-CoV-2 will follow suit.

“I expect SARS-CoV-2 infection rates, as well as potential disease outcomes, to be worse in winter,” says Akiko Iwasaki, an immunobiologist at the Yale School of Medicine in New Haven, Connecticut. Evidence suggests that dry winter air improves the stability and transmission of respiratory viruses, and the airway’s immune defenses can be compromised when dry air is inhaled, she adds.

Also, in colder weather, people are more likely to stay indoors where droplet transmission of the virus poses a greater risk, says Richard Neer, a computational biologist at the University of Basel in Switzerland.

Modeling by Neer’s group suggests seasonal fluctuations are likely to affect the spread of the virus and could make containment difficult in the northern hemisphere this winter.

In the future, outbreaks of SARS-CoV-2 may occur in waves every winter.

The risk for adults who have already had COVID-19 could be reduced, as with the flu, but that will depend on how quickly immunity to the coronavirus declines, Neer says.

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What’s more, combining COVID-19, influenza and RSV in fall and winter can be challenging, says Velasco-Hernandez, who is creating a model for how such viruses might interact.

It is not yet clear if infection with other human coronaviruses can provide any protection against SARS-CoV-2.

In a cell culture experiment involving SARS-CoV-2 and the closely related SARS-CoV, antibodies from one coronavirus could bind to another coronavirus, but did not disable or neutralize it.

To end the pandemic, the virus must either be eradicated globally, which most scientists believe is nearly impossible due to how widespread it has spread, or people must build up sufficient immunity through infections or vaccines. It is estimated that 55–80% of the population should be immune, depending on the country.

Unfortunately, early evidence suggests that there is still a long way to go. Antibody testing estimates that show only a small fraction of people are infected, and disease simulations support this.

A study in 11 European countries estimated that the infection rate was 3-4% prior to May 4, based on the infection-to-death ratio and the number of deaths. In the United States, antibody prevalence ranged from 1% to 6.9%, depending on the region.

What will happen in 2021 and beyond?

The progression of a pandemic over the next year will largely depend on the development of the vaccine and how long the immune system maintains its protective function after vaccination or recovery from infection.

Many vaccines provide protection for decades – for example against measles or polio – while others, including whooping cough and the flu, fade over time. Likewise, some viral infections cause strong immunity, others a more temporary response.

“The overall incidence of SARS-CoV-2 through 2025 will be critically dependent on the duration of immunity,” wrote Harvard epidemiologist Mark Lipsitch and colleagues in a May article exploring possible scenarios.

Researchers know little about how long immunity lasts against SARS-CoV-2. One study of convalescent patients showed that neutralizing antibodies persisted for up to 40 days after the onset of infection; several other studies show that antibody levels decline over weeks or months.

If COVID-19 follows the same pattern as SARS, antibodies can remain high for 5 months with a slow decline over 2 to 3 years.

However, antibody production is not the only form of immune defense; Memory B and T cells also protect against future encounters with the virus, and little is known about their role in SARS-CoV-2 infection.

It will take a long time for researchers to conduct research with large numbers of people to get a clear answer to the question of immunity, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota in Minneapolis.

“We’ll just have to wait.”

If the infection continues to grow rapidly without a vaccine or sustained immunity, “we will see a regular, widespread circulation of the virus,” says Grad. In this case, the virus will become endemic, it would be very painful. “

And it’s unthinkable: malaria, a preventable and curable disease, kills over 400,000 people every year.

“These worst-case scenarios are happening in many countries with preventable diseases, which are already causing huge human toll,” says Bhatt.

The Harvard team speculates that if the virus induces short-term immunity – similar to two other human coronaviruses, OC43 and HKU1, which have immunity to which lasts about 40 weeks – then people could become reinfected and there could be annual outbreaks.

An additional CIDRAP17 report, based on trends in eight global influenza pandemics, indicates significant COVID-19 activity for at least the next 18-24 months, either as a series of gradually decreasing peaks and troughs or as a “slow plateau” – ongoing transmission without a clear wave pattern. T

However, these scenarios remain only speculations, as the pandemic has not yet followed the pandemic influenza model, Osterholm says.

“We are in a coronavirus pandemic for which we have no precedent.”

Another possibility is that the immunity to SARS-CoV-2 will be permanent. In this case, even without a vaccine, it is possible that after a worldwide outbreak, the virus will burn out and disappear by 2021. However, if the immunity is moderate and lasts about two years, then it may turn out that the virus will return by 2024.

This projection does not take into account the development of effective vaccines.

“A vaccine is likely to be found, given the tremendous amount of effort and money invested in this area and the fact that some candidates are already undergoing human trials,” Velasco-Hernandez says.

Even a vaccine that provides incomplete protection can help reduce the severity of the disease and prevent hospitalization. However, it will take months to develop and distribute a successful vaccine.

COVID-19 does not affect the world equally. In regions with older populations, there may be a disproportionate increase in cases in the later stages of the epidemic; a mathematical model, published in June and based on data from six countries, suggests that the susceptibility to infection in children and people under 20 years of age is about half that of the elderly.

All countries, cities and communities affected by the pandemic have one thing in common.

“There is still a lot we don’t know about this virus,” scientists say. “Until we have more accurate data, we will have a lot of uncertainty.”

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