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.