The arrival of the COVID-19 vaccine in Colorado last week delivered something we’ve had very little of in 2020: hope. After accepting the state’s first shipment of the Pfizer vaccine on December 14, Governor Jared Polis cheered and clapped. “The end of the pandemic is in sight,” he said.

What’s less certain, though, is how quickly the end will arrive.

To effectively beat the virus, we’ll need to achieve herd immunity, says Jonathan Samet, MD, dean of the Colorado School of Public Health. Herd immunity, also known as community immunity, means enough people are immune to the virus that it can no longer spread widely. To achieve herd immunity from SARS-CoV-2 (the virus that causes COVID-19), Samet says roughly 70 percent of the population needs to develop immunization one of two ways: via vaccination or natural infection. Because the bulk of that immunization will come from vaccination, “we need the majority of Coloradans to be vaccinated,” says Samet. If enough of the population gets vaccinated, the epidemic will end.

James Neid, MD, infectious disease specialist at the Medical Center of Aurora, says it’s difficult to predict when, exactly, that will happen, but hopes that activities like in-person schooling and public gatherings will resume by fall 2021. But a number of things have to occur for that hope to become reality, according to Neid.

One big TBD is how many people will actually get vaccinated. According to a Healthier Colorado poll of 1,008 people taken last month, just 60 percent of respondents said they plan on taking the COVID-19 vaccine. Results from a national Kaiser Family Foundation survey released December 15 were more promising: 71 percent of 1,676 respondents said they would definitely or probably get a COVID-19 vaccine, if it was determined to be safe by scientists and available for free. But it’s difficult to know what to make of these polls until people are actually offered the vaccine, says Samet. There’s also a concern that vaccine efficacy may not be quite as high in the real world as it was in clinical trials, says Neid. Both Pfizer and Moderna report that their vaccines were around 95 percent effective in clinical trials. “That may or may not affect people’s desire to get the vaccine,” he says. The discovery of new side effects could also play a role.

Then there’s the issue of supply chain and distribution, Neid adds. Successfully manufacturing and then delivering hundreds of millions of doses of the vaccine to all corners of the country is a herculean task. There’s no guarantee Colorado will be able to stick to its phased vaccination plan, which says all residents will have access to the vaccine by next summer. The FDA’s emergency use authorization of the Moderna vaccine on December 18 certainly helps, but that same day, Gov. Polis announced in a news briefing that the state will receive 16,000 fewer doses of the Pfizer vaccine than expected in its second shipment.

Yet another unknown, says Samet, is how long immunity lasts from both natural infection and the vaccine. Getting the vaccine won’t be like a free pass to do whatever you want—at least for now. People who get vaccinated will still need to wear masks and physically distance, according to the Colorado Department of Public Health and Environment (CDPHE). That’s because current information suggests it’s still possible, post vaccination, to get “mild or asymptomatic infection or spread the virus to others,” per the CDPHE website. Neid is hopeful that more information will be released in the coming months that allows these restrictions to ease, but in the interim he stressed the importance of continued vigilance.

“If we lax up on masking, distancing, and hygiene prior to the arrival of the vaccine, the cases can get dramatically worse,” he warns. “And that means that the vaccine may or may not work as well as we had hoped.” Colorado’s COVID-19 case rate surged to record highs in November, but the spread now seems to be slowing. Still, the seven-day positivity rate, which was 7.76 percent as of December 20, remains above the 5 percent threshold experts say is needed to contain the virus. Neid advises Coloradans to stay committed to public health measures with the hope that restrictions will loosen as soon as cases start to drop. “Hopefully,” he adds, “the vaccine will just accelerate the time frame.” He says he feels “cautiously optimistic” about the rollout thus far.

As we look ahead to 2021, patience, it seems, will be essential. It will take a while before the vaccine has a big impact on the number of COVID-19 cases, hospitalizations, and deaths in Colorado. “I think it’s going to be a far slower transition than many of us want,” warns Samet. He predicts we’ll be wearing masks and physically distancing for a while longer. Over time, as the vaccine becomes increasingly available, he believes people will start to feel more comfortable traveling and seeing family and that restrictions on certain activities—like eating inside restaurants and in-person schooling—will ease. Vaccinated groups of people may decide to get together, Samet adds, “and probably that will be OK.” There’s also the possibility that viral transmission will naturally lessen in the spring as the weather warms and people spend less time indoors.

For now though, “we have to hunker down and wait,” says Samet. The dark winter is not yet over.