Epidemiologists worldwide have been developing models to predict how the coronavirus pandemic will progress throughout the rest of this year and the foreseeable future. Here's what they're forecasting.

What to expect for the rest of this year

While nearly every country is affected by the coronavirus pandemic, some countries are faring much better than others when it comes to managing outbreaks. Some countries—including China and New Zealand, for instance—currently are seeing comparatively low levels of new coronavirus cases, while others—including Brazil and the United States—are seeing persistently high rates of new cases. As such, experts predict that countries this year will continue to focus on efforts to get coronavirus outbreaks under control and keep them that way.

Experts note that changes in personal behavior—such as mask wearing, hand washing, and social distancing—can help to curb the coronavirus' spread. And evidence suggests that, in some countries, people are employing those practices even in the absence of mandated lockdowns, which could help to limit the virus' reach.

For example, a report from the MRC Centre for Global Infectious Disease Analysis at Imperial College London found that, in 53 countries that have eased their lockdowns, there hasn't been as much of a surge in new coronavirus infections as researchers at MRC had expected. Samir Bhatt, a co-author of the report and an infectious disease epidemiologist at Imperial College London, said, "It's undervalued how much people's behavior has changed in terms of masks, hand washing, and social distancing. It's nothing like it used to be."

Therefore, experts say that increasing or continuing those behaviors could help to drive down coronavirus infection rates. Researchers at Anhembi Morumbi University in Brazil even have predicted that, if 50% to 65% of people throughout the world took precautions to curb coronavirus transmission, countries could gradually ease social distancing measures every 80 days while still avoiding peaks in infection rates over the next two years.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has pointed out that, the better a population practices social distancing and other precautions to protect against coronavirus transmission, the quicker a country will get the coronavirus under control and be able to ease those practices. "This will be a long, long haul unless virtually everybody—or a very, very high percentage of the population, including the young people—take very seriously the kind of prevention principles that we've been talking about," he said.

Experts also say that countries should employ a combination of coronavirus testing, isolating people who test positive for the virus, and tracing the contacts of individuals who test positive—and research suggests those efforts must be robust and swift. For instance, researchers from the Centre for the Mathematical Modelling of Infectious Diseases Covid-19 Working Group in an analysis simulated outbreaks of varying contagiousness and found that, if contact tracing is done quickly and extensively—meaning that 80% of a newly diagnosed patient's contacts are traced within a few days—outbreaks can be controlled.

All of those mitigation efforts will be especially important as countries enter their winter seasons. "Things get a bit more dangerous" in the winter months, Bhatt said.

Experts predict that areas seeing colder temperatures during the second half of this year will also see increases in their rates of new coronavirus cases.

"I expect [the coronavirus] infection rate, and also potentially disease outcome, to be worse in the winter," Akiko Iwasaki, an immunobiologist at the Yale School of Medicine, said.

That's because cold temperatures tend to drive people indoors, where transmission of the virus is more likely, according to Richard Neher, a computational biologist at the University of Basel in Switzerland.

In addition, Iwasaki explained that research suggests dry winter air can improve the stability and transmissibility of respiratory viruses like the novel coronavirus, and immune defense within the respiratory tract could be weakened by dry air.

What to expect in 2021—and beyond

The future of the coronavirus pandemic long term largely will depend on two things, experts say: How strong of an immunity people build against the virus after being exposed, and the arrival of a vaccine against the virus.

Experts have suggested that outbreaks of the novel coronavirus potentially could occur every winter. However, Neher said it's possible that individuals who've already been exposed to the virus may have a reduced risk of becoming infected or developing a severe case of Covid-19, the disease caused by the virus, if they encounter it again—similar to the way our bodies currently react to the flu. That would depend on how quickly any immunity we gain against the new coronavirus wears off, Neher said.

As of now, not much is known about whether people do, in fact, build immunity against the coronavirus nor about how long that immunity may last—though research has led experts to develop a few theories.

"The total incidence of [coronavirus infection] through 2025 will depend crucially on this duration of immunity," Yonatan Grad, an epidemiologist at Harvard T.H. Chan School of Public Health, Marc Lipsitch, also an epidemiologist at Harvard, and colleagues wrote in a report published in Science in May.

If the novel coronavirus follows a similar pattern to the coronavirus that causes SARS, for instance, antibodies a person develops against the new coronavirus could last at a high level for five months, and then slowly decline over two to three years, Grad, Lipsitch, and colleagues surmised. Under such a circumstance, people would build moderate immunity to the virus, which could mean that the virus could temporarily vanish for a few years and then resurge, they explained.

And if people develop permanent immunity to the novel coronavirus after exposure, transmission of the virus could burn out and nearly vanish by 2021, they noted.

However, if people don't gain any type of long-lasting immunity or we're without a vaccine, "we will see regular, extensive circulation of the virus," Grad said. "That would be really painful," but also not unheard of, Grad explained.

For example, malaria, which is a treatable and preventable disease, circulates and kills over 400,000 people every year, Nature reports.

"These worst-case scenarios are happening in many countries with preventable diseases, causing huge losses of life already," Bhatt said.

But none of those scenarios account for the possibility of a vaccine against the novel coronavirus, which could drastically affect and potentially even halt the pathogen's transmission, experts note.

One thing experts know for sure, though, is "[t]here is so much we still don't know about this virus," Juliet Pulliam, director of the South African Centre for Epidemiological Modelling and Analysis at Stellenbosch University, said. "Until we have better data, we're just going to have a lot of uncertainty" (Scudellari, Nature, 8/5; Dennis et. al., Washington Post, 8/11).