A 90 percent effectiveness is very impressive, but the rate is based on a relatively small number of people. (Pixabay/)

On Monday, pharmaceutical company Pfizer announced the latest results for their coronavirus vaccine, which is now in late-stage clinical trials. The results, which were evaluated by an independent committee of experts (though not yet peer-reviewed), show that based on the information they have thus far, the drug is at least 90 percent effective in preventing COVID-19 among participants who had not previously been infected with the novel coronavirus.

These results are promising, and are coming at a time when the world is anxiously awaiting positive news. However, there’s still a long way to go before researchers can be certain that this vaccine is indeed as effective as it seems.

“The results are really quite good, I mean extraordinary,” Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, told The Washington Post. Other outside experts expressed similar cautious optimism. “We need to see the actual data, and we’re going to need longer-term results,” Jesse Goodman, a professor of medicine and infectious diseases at Georgetown University, told The New York Times. Adding, “it’s a testament to hard work and science that we’re getting results that are so good and so fast.”

The results are based on a Phase 3 clinical trial which began back in July, enrolling nearly 44,000 people, with about half the cohort receiving the vaccine (in two doses, given over the course of a month) and the rest getting a placebo. The independent team of researchers who are responsible for reviewing the results are the only ones who know who got what. To evaluate the vaccine’s effectiveness, the researchers had to wait for enough people in the trial (in both the vaccine group and the placebo group) to catch COVID-19. This first analysis, announced today, is based on 94 participants who contracted the novel viral illness.

A 90 percent effectiveness is indeed very impressive—it’s on par with some of the most successful vaccines, similar to the measles shot. However, the rate is based on a relatively small number of people, and it isn’t clear from the publicly available data just how many of those infected volunteers received the placebo. Kathrin Jansen, a senior vice president at Pfizer and the head of its vaccine research and development, told The New York Times that the outside review board analyzing the results didn’t say how many of those 94 people had received the placebo, but that given the 90% effectiveness rate, at most nine people in the vaccine arm of the trial have gotten COVID-19 so far. But it’s worth noting that Pfizer hasn’t been following participants for very long, so it remains to be seen how many people in the trial will contract the coronavirus in the long run.

Pfizer says that the vaccine trial is still ongoing and the company won’t seek approval from the FDA until at least 164 people have contracted COVID-19. This many come sooner than later, however. Infection rates are setting new records not just in the United States, but worldwide. The drug maker didn’t expect to be able to get these results as soon as it did, but says the spike in cases around the world has made the results come in sooner than they expected, and reaching that 164 benchmark may occur sooner than later as well.

The company also plans to evaluate how well the vaccine is working not just in terms of preventing infection, but also in protecting against developing severe forms of the disease.

Pfizer also hasn’t reported any serious side effects in those who have received the vaccine. The drug, which was initially developed by German pharma company BioNTech (who later partnered with Pfizer to continue to bring the vaccine to market) employs a newer technology that has yet to be used in an FDA-approved vaccine. The drug contains messenger RNA (mRNA), whose role is to carry genetic code from DNA inside the cell’s nucleus to the ribosomes, which make proteins. The vaccine contains mRNA with instructions to create a protein that’s found on the surface of the coronavirus. Once created, the immune system reacts to these proteins, generating protection against the virus if it ever invades a person’s body. Another promising coronavirus vaccine currently being developed by Moderna uses a similar approach.

It’s not yet clear when all the necessary remaining data will be completed and be made available—it largely depends on when the remaining 70 infections will occur. However, Pfizer says that it plans to request emergency use authorization from the FDA later this month.

Even if everything goes well with the trial, manufacturing and distributing the vaccine will be another logistical challenge. Treatments that use mRNA must be kept at extremely cold temperatures (Pfizer’s must be kept at -94°F, and Moderna’s at -4°F), and the drug needs to be given two times over the course of a month (the second dose is given three weeks after the first). It’s this process that Operation Warp Speed, the federally organized collaboration to bring a vaccine to Americans as soon as possible, comes into play.

The US government has pledged it would provide Pfizer nearly $2 billion to provide 100 million doses of the vaccine to Americans at no cost. However, Pfizer has made clear that this money is only for the distribution and delivery of the vaccine, and hasn’t accepted any funding from the U.S. government or others to develop its vaccine, with a main goal of keeping politics out of creating an effective—and, most importantly, safe—vaccine. Then comes the final hurdle: getting people to actually get the shot. Only about half of Americans say they’d get a COVID-19 vaccine, but we’ll need significantly more than that to produce herd immunity. Even the best vaccine will be held back if people aren’t willing to get it.