The End of the Pandemic Is Now in Sight
A year of scientific uncertainty is over. Two vaccines look like they will work, and more should follow.
For all that scientists have done to tame the biological world, there are still things that lie outside the realm of human knowledge. The coronavirus was one such alarming reminder when it emerged with murky origins in late 2019 and found naive, unwitting hosts in the human body. Even as science began to unravel many of the virus’s mysteries—how it spreads, how it tricks its way into cells, how it kills—a fundamental unknown about vaccines hung over the pandemic and our collective human fate: Vaccines can stop many, but not all, viruses. Could they stop this one?
The answer, we now know, is yes. A resounding yes. Pfizer and Moderna have separately released preliminary data that suggest their vaccines are both more than 90 percent effective, far more than many scientists expected. Neither company has publicly shared the full scope of their data, but independent clinical-trial monitoring boards have reviewed the results, and the FDA will soon scrutinize the vaccines for emergency use authorization. Unless the data take an unexpected turn, initial doses should be available in December.
The tasks that lie ahead—manufacturing vaccines at scale, distributing them via a cold or even ultracold chain, and persuading wary Americans to take them—are not trivial, but they are all within the realm of human knowledge. The most tenuous moment is over: The scientific uncertainty at the heart of COVID-19 vaccines is resolved. Vaccines work. And for that, we can breathe a collective sigh of relief. “It makes it now clear that vaccines will be our way out of this pandemic,” says Kanta Subbarao, a virologist at the Doherty Institute, who has studied emerging viruses.
The invention of vaccines against a virus identified only 10 months ago is an extraordinary scientific achievement. They are the fastest vaccines ever developed, by a margin of years. From virtually the day Chinese scientists shared the genetic sequence of a new coronavirus in January, researchers began designing vaccines that might train the immune system to recognize the still-unnamed virus. They needed to identify a suitable piece of the virus to turn into a vaccine, and one promising target was the spike-shaped proteins that decorate the new virus’s outer shell. Pfizer and Moderna’s vaccines both rely on the spike protein, as do many vaccine candidates still in development. These initial successes suggest this strategy works; several more COVID-19 vaccines may soon cross the finish line. To vaccinate billions of people across the globe and bring the pandemic to a timely end, we will need all the vaccines we can get.
But it is no accident or surprise that Moderna and Pfizer are first out of the gate. They both bet on a new and hitherto unproven idea of using mRNA, which has the long-promised advantage of speed. This idea has now survived a trial by pandemic and emerged likely triumphant. If mRNA vaccines help end the pandemic and restore normal life, they may also usher in a new era for vaccine development.
The human immune system is awesome in its power, but an untrained one does not know how to aim its fire. That’s where vaccines come in. They present a harmless snapshot of a pathogen, a “wanted” poster, if you will, that primes the immune system to recognize the real virus when it comes along. Traditionally, this snapshot could be in the form of a weakened virus or an inactivated virus or a particularly distinctive viral molecule. But those approaches require vaccine makers to manufacture viruses and their molecules, which takes time and expertise. Both are lacking during a pandemic caused by a novel virus.
mRNA vaccines offer a clever shortcut. We humans don’t need to intellectually work out how to make viruses; our bodies are already very, very good at incubating them. When the coronavirus infects us, it hijacks our cellular machinery, turning our cells into miniature factories that churn out infectious viruses. The mRNA vaccine makes this vulnerability into a strength. What if we can trick our own cells into making just one individually harmless, though very recognizable, viral protein? The coronavirus’s spike protein fits this description, and the instructions for making it can be encoded into genetic material called mRNA.
Both vaccines, from Moderna and from Pfizer’s collaboration with the smaller German company BioNTech, package slightly modified spike-protein mRNA inside a tiny protective bubble of fat. Human cells take up this bubble and simply follow the directions to make spike protein. The cells then display these spike proteins, presenting them as strange baubles to the immune system. Recognizing these viral proteins as foreign, the immune system begins building an arsenal to prepare for the moment a virus bearing this spike protein appears.
“What a relief,” says Barney Graham, a virologist at the National Institutes of Health, who helped design the spike protein for the Moderna vaccine. “You can make thousands of decisions, and thousands of things have to go right for this to actually come out and work. You’re just worried that you have made some wrong turns along the way.” For Graham, this vaccine is a culmination of years of such decisions, long predating the discovery of the coronavirus that causes COVID-19. He and his collaborators had homed in on the importance of spike protein in another virus, called respiratory syncytial virus, and figured out how to make the protein more stable and thus suitable for vaccines. This modification appears in both Pfizer/BioNTech’s and Moderna’s vaccines, as well as other leading vaccine candidates.
Experts anticipate that the ongoing trials will clarify still-unanswered questions about the COVID-19 vaccines. For example, Ruth Karron, the director of the Center for Immunization Research at Johns Hopkins University, asks, does the vaccine prevent only a patient’s symptoms? Or does it keep them from spreading the virus? How long will immunity last?
How well does it protect the elderly, many of whom have a weaker response to the flu vaccine? So far, Pfizer has noted that its vaccine seems to protect the elderly just as well, which is good news because they are especially vulnerable to COVID-19.
Several more vaccines using the spike protein are in clinical trials too. They rely on a suite of different vaccine technologies, including weakened viruses, inactivated viruses, viral proteins, and another fairly new concept called DNA vaccines. Never before have companies tested so many different types of vaccines against the same virus, which might end up revealing something new about vaccines in general. You now have the same spike protein delivered in many different ways, Sette points out. How will the vaccines behave differently? Will they each stimulate different parts of the immune system? And which parts are best for protecting against the coronavirus? The pandemic is an opportunity to compare different types of vaccines head-on.
If the two mRNA vaccines continue to be as good as they initially seem, their success will likely crack open a whole new world of mRNA vaccines. Scientists are already testing them against currently un-vaccinable viruses such as Zika and cytomegalovirus and trying to make improved versions of existing vaccines, such as for the flu. Another possibility lies in personalized mRNA vaccines that can stimulate the immune system to fight cancer.
Distributing the limited vaccines fairly and smoothly will be a massive political and logistical challenge, especially as it begins during a bitter transition of power in Washington. The vaccine is a scientific triumph, but the past eight months have made clear how much pandemic preparedness is not only about scientific research. Ensuring adequate supplies of tests and personal protective equipment, providing economic relief, and communicating the known risks of COVID-19 transmission are all well within the realm of human knowledge, yet the U.S. government has failed at all of that.
The vaccine by itself cannot slow the dangerous trajectory of COVID-19 hospitalizations this fall or save the many people who may die by Christmas. But it can give us hope that the pandemic will end. Every infection we prevent now—through masking and social distancing—is an infection that can, eventually, be prevented forever through vaccines.