BY Fast Company Contributor 3 MINUTE READ

There’s some massive news out about COVID-19—and it’s good for a change.Yes, it’s very good news—yet it’s important to keep hopes and expectations in check.

Pfizer and BioNTech’s vaccine is reportedly successful in preventing over 90% of infections according to early data from its Phase 3 study, says STAT News. Needless to say, if the data holds as the study continues, this vaccine could be the thing that turns the tide of the COVID-19 pandemic in humanity’s favor.

However, it’s also important to stress that the results are preliminary and a successful vaccine isn’t a given yet. Here are six things to understand about Pfizer and BioNTech’s COVID-19 vaccine so far:

1) The vaccine appears to work in more than 90% of cases: This is huge. Early results show the vaccine has a greater than 90% efficacy rate. That means over 9 out of 10 people who get the vaccine will gain immunity from it. To put that in perspective, health experts have previously said that a COVID-19 vaccine with an efficacy rating of between 60% to 70% would be a big win. Some governments would even approve a vaccine with only a 50% efficacy rating. But 90%? That’s better than most scientists and public health experts have dared to dream.

2) The vaccine requires two doses: If this vaccine ends up being successful, a person will require at least two doses of it at least three weeks apart. That means the vaccine isn’t a one-and-done deal—which could raise logistical and supply chain challenges. After all, if two doses are required, you need to be able to make—and distribute—at least 14 billion doses to inoculate every person on earth.

3) We don’t know if the vaccine works on severe COVID-19 cases or how long it will be effective: A big unknown is how long and for whom the vaccine is 90% effective. Pfizer says it’s not yet evident whether the vaccine works on those who make up the worst COVID-19 cases—people who require hospitalization for the disease. It’s also unknown how long the immunity gained from the vaccine actually lasts. It could be forever, or it could be just for a few months. We just don’t know yet.

4) We don’t know if vaccinated people can still carry the disease: Another big unknown is whether vaccinated people can still be carriers of SARS-CoV-2, the virus that causes COVID-19. If recipients can still be carriers of the virus, they could still spread the disease to others even though they themselves would be, presumably, immune to its effects.

5) The results have not been peer-reviewed: It’s also important to note that Pfizer and BioNTech’s findings have not been peer-reviewed. That doesn’t mean their findings are incorrect. However, it does mean they need to still pass the scientific method’s most rigorous process.

6) If approved, most people will be waiting a while to get the vaccine: The vaccine could receive FDA emergency use authorization (EUA) before the end of the year. It all depends on how the ongoing Phase 3 study progresses. The third week of November is the next milestone, which is when Pfizer will have two months of data on volunteers who have had their second dose of the vaccine. If there are no worrying side-effects, the vaccine could get EUA approval by the end of the year. If that’s the case, Pfizer says 50 million doses worldwide would be available by the end of 2020, with another 1.3 billion doses available by the end of 2021. Yet that still leaves almost 6 billion people who won’t get the vaccine until 2022 at the earliest (barring the approval of other vaccines).

In short: This is very promising news. But it’s wise to keep expectations and hopes in check until Pfizer can complete its Phase 3 study and the results can be peer-reviewed. But as William Gruber, Pfizer’s senior vice president of vaccine clinical research and development, told STAT, “I’ve been in vaccine development for 35 years. I’ve seen some really good things. This is extraordinary.” He added, “This really bodes well for us being able to get a handle on the epidemic and get us out of this situation.”