Experts celebrated the news that Pfizer’s vaccine could potentially prevent 90 percent of Covid-19 cases, but the road ahead is still very long and very uncertain.

Pfizer and BioNTech, a German biotechnology company, announced Monday that their coronavirus vaccine may be 90 percent effective at preventing Covid-19, according to early results. Although experts cautioned that more detailed results need to be released, they see it as a very promising development both for this vaccine and for other vaccines under development. It’s the first step in the monumentally complicated process of getting the population vaccinated—but only the first step. Manufacturing and distributing the vaccine will be just as challenging.

The two companies said in a press release that 94 participants in their phase 3 trial have had confirmed cases of Covid-19, but the vast majority of those confirmed cases happened among subjects receiving the placebo. These results have not been featured in a peer-reviewed publication, which is not especially surprising, since the trial is ongoing and the independent monitoring board may not have even shared all of the results with the companies yet. However, these scant details leave the vaccine-desperate public with a lot of unanswered questions. Read more at The New Republic.