STAT’s Helen Branswell writes that with a little luck and a lot of science, the world might in the not-too-distant future get vaccines against Covid-19. But those vaccines won’t necessarily prevent all or even most infections.
In the public imagination, vaccines are often seen effectively as cure-alls, like inoculations against measles.
Rather than those vaccines, however, the Covid-19 vaccines in development may be more like those that protect against influenza — reducing the risk of contracting the disease, and of experiencing severe symptoms should infection occur, a number of experts told STAT.
“We all recognize that flu vaccine, in a year when it’s efficacious, you have what, 50% protection? And in a year when it’s poor you have 30% or less than that — and still we use that,” said Marie-Paule Kieny, who is chairing a committee advising the French government on vaccines to prevent Covid-19.
Ideally, vaccines would prevent infection entirely, inducing what’s known as “sterilizing immunity.” But early work on some of the vaccine candidates suggests they may not stop infection in the upper respiratory tract — and they may not stop an infected person from spreading virus by coughing or speaking.
A recently released study in which macaques were vaccinated with one vaccine candidate — this one being developed by Oxford University and AstraZeneca — showed the primates were protected from Covid-induced pneumonia. But the macaques still had high levels of virus replicating in their upper airways. (The paper was a pre-print, meaning it hasn’t yet been peer-reviewed and published in a journal.)
Vincent Munster, who leads the team that conducted that study, said a vaccine that could mitigate the severity of the Covid-19 pandemic would still be a significant contribution in a world struggling to co-exist with a dangerous new virus.
“If we push the disease from pneumonia to a common cold, then I think that’s a huge step forward,” said Munster, chief of the virus ecology unit at the National Institute of Allergy and Infectious Diseases’ Rocky Mountain Laboratories in Hamilton, Mont.
The rush to develop vaccines means that ideal solutions may be out of reach in the immediate term; Munster said he anticipates seeing second-generation vaccines that could be more protective. Other scientists, though, are cautious about how much the world can expect from vaccines against this pathogen.
Michael Mina, an infectious diseases epidemiologist at Harvard’s T.H. Chan School of Public Health, thinks achieving sterilizing immunity with a vaccine will not be possible for Covid-19. Experience with human coronaviruses — and with multiple pathogens that cause colds — shows immunity that develops after infection with respiratory tract infections is not lifelong. In some cases, the duration is measured in months, not years.