Pfizer said the coronavirus vaccine made in collaboration with German partner BioNTech proved 90% effective, which is extremely rare for a vaccine and especially for one made on such an expedited time frame. The company has not yet released a complete data set from its Phase III trial.

As impressive as the accomplishment is, several epidemiologists note that the battle against COVID is far from over. The process to get a vaccine into Americans’ hands continues as Pfizer navigates issues ranging from Food and Drug Administration (FDA) emergency authorization to manufacturing to distribution.

“The news from Pfizer is encouraging, but more details are needed, such as whether the same rate of effectiveness was seen across different patient populations and how long that efficacy lasts,” said Dr. Elaine Hanh Le, chief medical officer of the health information firm Healthline, in an emailed statement. “Very few vaccines have such a high efficacy rate, and ultimately, for a vaccine to be truly effective, it needs to be broadly adopted by all in the community. Until then, we need to remain vigilant as we continue to wear our masks, keep a physical distance of at least six feet from others, wash your hands, and avoid crowds indoors.”

Pfizer has ambitious manufacturing goals. In September, the drugmaker and BioNTech reached an agreement to provide the European Union up to 300 million doses; the United States an initial 100 million doses; and eventually 1.3 billion worldwide doses of the vaccine by the end of 2021—although just 50 million doses are expected globally by the end of the year—should it prove effective and win FDA authorization.

Monday’s announcement is cause for optimism, but Pfizer will have to continue monitoring clinical trial participants who received two doses of the vaccine for two months to make sure there are no lasting safety issues. The company expects to have that information by the third week of November, setting it up for a potential late-November FDA application. Regulators will then take at least two or three weeks to review the data and make a decision.

The other question is who will receive the first doses. Given that this particular COVID vaccine requires two doses several weeks apart, the 50 million expected to be delivered by the end of 2020 would reach only about 25 million people. And an emergency authorization isn’t the same thing as full-on approval for a therapy despite President Donald Trump’s implication that everyone would be able to get a vaccine within months.

In reality, doses of what would be a hotly sought coronavirus shot would have to be triaged and prioritized for the most vulnerable and high-risk people, including the elderly and those with diabetes or heart conditions. Widespread market availability is unlikely until mid-2021, underscoring how important it is to keep up social distancing and other public safety measures.

Finally, there’s the distribution process, which will require widespread cooperation among drugmakers, governments, and logistics firms. The type of vaccine that Pfizer is working on, a so-called mRNA vaccine, requires storage at temperatures of about negative 112 degrees Fahrenheit.

That forced Pfizer to get creative and create a specialized carrying case alongside its vaccine that can store doses at those temperatures and thus ease distribution across the globe. (It also comes armed with GPS and thermal sensors so the companies can keep tabs on doses at any given time.)

“The logistics of medicines and distribution of medicines are always very complicated, because there are always storage conditions,” said Pfizer CEO Albert Bourla at Fortune’s virtual Global Forum last month. “And we knew that we had to move very fast. So we wanted to make sure that we can distribute by plane. We can distribute by any type of vehicle without needing refrigeration individually.”