Last spring and summer, when a COVID-19 vaccine was only a glimmer of hope on the horizon, scientists warned in their careful way that vaccines might not live up to the public’s high expectations. The FDA said a vaccine needed to be just 50 percent effective. The most important thing, scientists told me, was that the vaccines at least protect against severe illness.
Then, in the fall, data from the Pfizer and Moderna vaccine trials demonstrated 95 percent and 94 percent efficacy, respectively, against all symptomatic infections. They smashed expectations—and created new ones. In comparison, the results from other vaccine trials look pretty good but unspectacular: AstraZeneca’s vaccine looks to be 70 percent effective; Novavax’s achieved 89 percent efficacy in the U.K., but only 49 percent in South Africa, based on data released yesterday; and Johnson & Johnson’s demonstrated 66 percent efficacy against moderate and severe infection, based on results released today. These numbers are not directly comparable because the different trials were run in different countries, with slightly different protocols, against different versions of the virus. The lower efficacy in South Africa results is likely related to a new variant of the coronavirus, which seems to have evolved to escape immunity.
But beneath these top-line numbers is a consistent pattern: All of the vaccines are very good at preventing severe illness and death from COVID-19. That was the original goal for the vaccines, and it is still the most important. “We’re most interested in our ability to keep people out of the hospital and keep people alive,” says Natalie Dean, a biostatistician at the University of Florida.
Biologically, it makes sense that COVID-19 vaccines would be better at preventing severe infections than mild infections. Think of a vaccine as a dimmer, rather than a light switch. Each shot induces some protective immunity against the coronavirus, even if it doesn’t protect completely. Someone who might have died of COVID-19 without the vaccine could survive with supplemental oxygen. Someone who might have needed hospitalization might experience only a mild infection. A vaccine that confers partial immunity is still better than no vaccine.
As it stands, even the lowest efficacy from these vaccines—49 percent against the South Africa variant—is roughly comparable to the efficacy of the annual flu vaccine. Before the results of the mRNA vaccines from Pfizer and Moderna raised expectations, scientists hoped for something similar to the flu shot. “Even that 50 percent range, given the severity of illness and death toll, would have been a game changer,” says Kelly Moore, the deputy director of the Immunization Action Coalition, a nonprofit that works with the CDC and others on disseminating vaccine information.
The non-mRNA vaccines have logistical advantages, too. The AstraZeneca, Novavax, and Johnson & Johnson vaccines can all be stored at normal fridge temperatures. In addition, the Johnson & Johnson vaccine is one dose, not two. A one-dose regimen means half as many syringes, half as many appointments, and a much simpler tracking system, making the vaccine much easier to deliver to remote and underserved communities.
How quickly these vaccines can help contain a global pandemic will depend on how quickly they can be produced. Johnson & Johnson has fallen behind on its manufacturing and is not expected to catch up until April, according to The New York Times. Novavax’s U.S. trial was delayed because of manufacturing challenges.
Additional vaccines—with different mechanisms and different efficacies—do further complicate the messages that public-health officials have to deliver. “These new vaccines provide great opportunities, but they also provide terrific communications challenges,” says Moore. Some people might be tempted to hold out for what looks like a more effective COVID-19 vaccine. But as Moore emphasizes, “any degree of protection is going to be better than putting off protection. This is not the time to be picky. I strongly recommend you go ahead and get it.” Johnson & Johnson is also testing a two-dose regimen for its vaccine; given how vaccines usually work, two doses will almost certainly be more protective than one.
It may be that no matter which vaccine you start with, you’ll eventually need a booster—or even multiple boosters, similar to annual flu shots. Vaccine makers are already working to update their vaccines against the South Africa variant. A second variant, from Brazil, has several of the same key mutations and may also decrease vaccine efficacy. And although the vaccines seem equally effective against the U.K. variant, it is more transmissible and becoming only more dominant in the U.K. and elsewhere. The longer the coronavirus runs unchecked and the more people it infects, the more opportunities for dangerous new variants to arise. The global vaccination effort is now in a race against the evolution of the virus—and the more vaccines we have, the better our collective chances.