It's been months since David Rubin's children have seen their 87-year-old grandmother, and only from a distance because of coronavirus. But Rubin, an epidemiologist at Children's Hospital of Philadelphia, is now making plans for a family reunion this summer - hunting for a rental property big enough to fit four families. 

"As a modeler, my mind works in terms of probabilities, and the probability of a great summer is really increasing," Rubin, director of the hospital's PolicyLab, said.

There is a good chance that by summer, America will look and feel very different than our current isolated lives. Eating inside a restaurant or a friend's house may no longer be controversial. Cookouts and summer vacations may return. Many aspects of life will be reminiscent of a time before coronavirus - as long as vaccinations continue to increase and Americans stay careful during the spring, when more highly-transmissible variants could proliferate and lead to an increase in cases, according to interviews with more than a dozen epidemiologists, modelers and virologists.

"There are wild card factors that could change this, but I've been telling people if there are things you've been wanting to do, think July or late summer," said Jeffrey Shaman, an infectious-disease expert who leads the modeling team at Columbia University.

Some of the growing reasons for optimism: Cases, hospitalizations and deaths have fallen steeply the past few weeks in the U.S. and worldwide. The World Health Organization reported an 11% global decline in cases last week, and a 20% drop in deaths. More than 46 million Americans have received at least one dose of coronavirus vaccine, and supply is poised to increase dramatically. This week, a third vaccine was found to be safe and effective and will likely be approved for emergency use within days.

Widespread vaccination is the key to having the kind of summer everyone wants - even if there is an increase in cases during early spring. By July 1, roughly 46% of the U.S. population - about 153 million people - could be vaccinated, according to projections by data scientist Youyang Gu, whose past models have been cited by the Centers for Disease Control and Prevention.

President Joe Biden said the U.S. will have enough supply to vaccinate 300 million Americans by the end of July; Anthony Fauci, the government's leading infectious-disease expert, predicted this month that all Americans will likely be eligible to receive a vaccine by late May or early June. And long before that, the country's oldest and most vulnerable will have been fully vaccinated, sending the death rate plummeting.

Residents at one senior living community in Virginia Beach have already glimpsed what that future may look and feel like. Nearly all of the 700 seniors at Westminster-Canterbury on Chesapeake Bay have now received their second vaccine dose, and 80% of the staff.

"There's just pure joy in the air, a feeling of renewal that's just palpable," said John Wolfe, president of the resident's association.

There hasn't been an active covid case since late December. Last Sunday, the facility held its first in-person church service at its chapel, though everyone still wore masks for safety. For months, those in the independent living apartments have worn wristbands so that people going out for groceries and errands wouldn't mingle with those choosing to eat in the dining hall. On Saturday, they held a special event to cut off those wristbands.

"It's like the light at end of tunnel has finally arrived," said Wolfe, 79.

Weather is another reason experts are optimistic about summer: warmer temperatures will allow more people to congregate outside, where conditions are less hospitable to the spread of the virus, rather than indoors, where coronavirus thrives.

For the past year, Natalie Dean, an assistant professor of biostatistics at University of Florida, has dreamed of bringing her children to visit their grandparents in Massachusetts. By summer, transmission will hopefully be low enough to make a flight safe for her family. The vaccine will allow the grandparents to see her children without fearing the virus could kill them.

"The virus won't be gone by summer, but we'll at least have some joy back in our lives," she said.

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But if the past year has taught researchers one thing, it is how wily, resourceful and unpredictable coronavirus can be. Experts who believe that summer could be relatively normal remain cautious about the near-term as highly-transmissible variants are circulating that could cause a spring spike in cases and as pandemic-weary Americans tire of restrictions. Continuing to be careful for just a little longer as more people get vaccinated can help ensure the summer people want to have, experts said.

"It's clear there isn't going to be some on/off switch where we wake up and the virus is gone," said Angela Rasmussen, a virologist at Georgetown University. "How it all turns out depends on a lot on the virus' behavior but also on us humans and what we choose to do."

And the sharp decrease in cases over past few weeks appears to have slowed.

"The latest data suggest that these declines may be stalling. Potentially leveling off," said CDC director Rochelle Walensky Friday. "It's still a very high number. We at CDC consider this a very concerning shift in the trajectory."

She added: "We may be done with the virus, but clearly the virus is not done with us."

Growing concerns about a spring increase in cases are compounded by officials easing restrictions. Iowa and Montana have lifted mask mandates. New York is reopening stadiums for concerts. California and Washington, D.C., are now allowing indoor dining. Roughly 30,000 fans recently flocked to the Daytona 500 NASCAR race.

"Reopening just as these variants are spreading is not smart," Tom Frieden, former director of the Centers for Disease Control and Prevention. "We're like a punch drunk boxer, getting up just as our opponent is preparing to deliver an even faster punch. ... By reopening we're leaning into that left hook. Why can't we ever learn?"

Some variants have been shown to evade the immune response and have caused infection in some people who were vaccinated or previously infected. But experts believe the vaccines still protect robustly against severe illness and death - like how someone who received a flu shot can still get a fever and chills from influenza, but is less likely up in the hospital.

"The vaccines are starting at such a high place of efficacy. Even if the variants start to wear that down, they should continue to have a huge effect on hospitalization and death," Dean said.

And as transmission falls, the country will be better able to control any hotspots that may flare using testing, contact tracing and isolation and targeted vaccination campaigns. Over time, the novel coronavirus will remain a threat, but one likely evolving to be like the seasonal flu or common cold.

Rasmussen said public officials urgently need to convey that message of hope so that Americans reeling from a long winter will continue to wear masks and distance this spring and buy time for the rapid increase of vaccinations. Only then will the glorious summer many are imagining become a reality.

"Everybody's burned out and exhausted. They're hitting their mental breaking points," said Rasmussen. "But we're in the last stretch of this terrible marathon, and people need hope so they'll be able to make that last dash to the finish line."

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Beyond this summer, the picture grows fuzzier, but many remain optimistic.

"I believe we'll be approaching normalcy by the end of this year. And God willing, this Christmas will be different than the last," Biden said earlier this month.

Winter, when more people are indoors, could bring an increase in cases and the return of some precautions or restrictions, though that is far from certain.

"We may see some peak in cases next winter, but as long as the vaccine remains effective, you will not see this level of death," said Ali Mokdad, an epidemiologist at the Institute for Health Metrics and Evaluation at the University of Washington.

Vestiges of the pandemic will remain. Masks may still be necessary in 2022, Fauci said. People might think twice about packing into a crowded bar or screaming at an indoor concert.

"I also don't think we'll look at certain activities the same way," Dean said. "Packing ourselves in the middle of a crazy crowd. I'll need more time to work up to that."

It remains unknown how many people will still hesitate or refuse to get vaccinated once supply is flowing freely or how underfunded, overworked public health departments will be able to meet sudden demand. And it is unclear how well the vaccines block transmission of the virus.

Additional variants could also be a wild card. The virus has made clear it is here to stay, and scientists need to stay alert to which ones emerge and proliferate. Vaccines might need to be updated to better protect against new variants.

Globally, there are concerns about how rich nations are hoarding shots, leaving little for poor ones. Unvaccinated countries, or and communities within the U.S. where many remain unvaccinated, could become reservoirs for the virus to continue to spread and mutate.

"If this pandemic has shown us anything, it's that we are all in this together to the end," said Shweta Bansal, a disease ecologist at Georgetown University.

In the U.S., it might take years to reach herd immunity - if it is ever reached. Experts estimate the threshold for herd immunity could lie somewhere between 70 and 85% of the population. One factor keeping it immediately out of reach is that no vaccine has yet been approved for the young. Children make up roughly 22% of the U.S. population. companies are just starting clinical trials for teenagers and adolescents.

Failing to reach herd immunity doesn't mean the situation will remain dire. As the country draws closer to that threshold in the summer and beyond, the pandemic will dwindle from a raging forest fire to more like a series of campfires that can be more easily managed.

"There are still many obstacles we have to get through," said Rubin, the epidemiologist at Children's Hospital. "But at least we can start making plans again."

He said he can already envision the family reunion this summer - hugging his 87-year-old mother, hanging out with siblings he's only seen online. "It's been such a long year. There's so much we have to catch up on."