COVID-19 vaccines could end the pandemic by eliminating severe cases
Here’s what it means for vaccines to prevent severe disease.
The Biden administration announced this week that it will purchase an additional 200 million doses of the COVID-19 vaccines from Pfizer and Moderna, which means the United States will have enough vaccine doses to immunize 300 million people (nearly all of the country’s 328 million residents) by the end of the summer.
In clinical trials, these vaccines boasted an efficacy rate of 94 to 95 percent at preventing symptomatic cases of COVID-19. There’s some early evidence the shots also reduce asymptomatic infections in people who are exposed to the virus after vaccination, although more research will be needed to confirm this. And, as the vaccine distribution ramps up over the next few months, there should be another boon: a huge drop in the occurrence of severe COVID-19.
“What it would mean for our healthcare system and for our societies to have that severe disease reduced would be huge,” says Stacey Schultz-Cherry, an infectious disease researcher at St. Jude Children’s Research Hospital in Memphis. “If we could cut down on severe disease, in some ways we would be able to go closer to normal.”
It’s expected that some proportion of people will still be vulnerable to infection after being vaccinated against a given disease, including COVID-19. However, research shows that vaccines can limit how ill people become if they do get infected. The seasonal flu shot reduces a person’s risk of being admitted to an intensive care unit or dying and shortens the duration of hospitalizations. “Even if the flu shot isn’t an exact match for the strain of virus that’s circulating, it will still prevent you from getting severe disease,” Schultz-Cherry says. “The same is true with measles; the measles vaccine is fantastic at preventing infection and reducing severe disease.”
COVID-19 vaccines also seem to lower the likelihood that people will become gravely ill if they do get infected. In unvaccinated people, the seriousness of COVID-19 varies wildly, from no symptoms to mild pneumonia to life-threatening illness. These extreme cases may involve an overactive or dysfunctional response from the body’s immune system.
“The vaccine-induced immune response allows the body to control the virus before you get all the way to the pathologic inflammatory response, the severe disease phase,” says Mark J. Mulligan, director of the NYU Langone Vaccine Center. “You kind of arrest things very early, so either maybe there is no disease or just very limited virus multiplication.”
The virus itself can also wreak havoc as it invades tissues throughout the body. “It really is the virus going in [and] causing damage on top of some other damage that your body will cause trying to fight the virus,” Schultz-Cherry says. “There are so many different things that we are seeing in these severe COVID patients.”
During clinical trials for the COVID-19 vaccines that have received emergency authorization, which includes Moderna’s and Pfizer’s, the researchers considered a number of criteria for severe COVID-19. Among these indicators were a racing heart, being put on a ventilator, shock, problems with the nervous system and organs, and admission to the ICU.
In Moderna’s clinical trial, all 30 participants who developed severe cases of COVID-19 had received the placebo rather than the vaccine candidate. During the trial for the vaccine from Pfizer and BioNTech, nine people in the placebo group and one in the vaccine group developed severe COVID-19. The U.S. Food and Drug Administration wrote that this participant met the criteria for severe COVID-19 because their blood oxygen levels fell just below the normal range. However, they were not hospitalized and didn’t seek further medical care, the agency noted.
“The vaccines are very effective at preventing severe disease, which basically amounts to respiratory failure or impending respiratory failure,” Mulligan says. “That was one of the truly impressive aspects of these trials.”
Over the course of the clinical trials, COVID-19 vaccines prevented severe disease across demographics such as age, race, and health status. “So far it looks like it’s doing pretty well across the board, at least in these early days, but there always is variability in people’s response, whether it be infection or vaccination,” Schultz-Cherry says. “Something we’ll have to really watch over time is, do your antibodies to COVID wane faster if you’re in a certain demographic?”
However, the degree of protection the vaccine offers is encouraging. “In general with vaccines, older individuals don’t respond as well,” Mulligan says. “That seems to be a little different here; the older adults are responding very well to these RNA vaccines.” This is crucial, he says, because older adults face a heightened risk of hospitalization and account for about eight out of 10 COVID-19 deaths in the United States.
Researchers have only had the opportunity to track the novel coronavirus for about a year. They’re still working to understand long-haul COVID-19, which involves symptoms that persist for weeks or months after the initial infection. There’s also concern that the virus may cause damage in seemingly mild cases that will show up later. “One of the scary things about this virus is we really don’t know, whether you have a severe infection or mild, what it means longer-term,” Schultz-Cherry says.
However, she and Mulligan are optimistic that vaccines will be able to ward off both severe COVID-19 and the potential for any lingering complications. “If the vaccine is preventing you from getting infected, meaning you don’t have any virus replicating in your respiratory tract, then yes, absolutely it would protect you from those long-term complications,” Schultz-Cherry says. “Even if you still have some virus replicating, but it’s much lower levels or can’t get deep in your lungs, you would also predict that you would have less long-term complications.”
Early data also indicate that the Moderna and Pfizer vaccines will be effective against new variants of the virus such as the one recently identified in the United Kingdom. The vaccines may be somewhat less potent against another variant of the virus that emerged in South Africa, but provoke antibody responses that likely remain high enough to offer protection. “Even if there is a little less efficacy, I think it will still do a very nice job preventing and limiting disease severity,” Schultz-Cherry says.
However, it will be important to continue surveilling the novel coronavirus even as vaccines become more accessible. As the virus continues to mutate over time, Mulligan says, “We may see some erosion of the absolute protection against laboratory-confirmed COVID or perhaps of an ability to prevent severe disease.”
In addition to sparing people who catch COVID-19 from life-threatening illness, the ability of vaccines to avert severe cases will be vital for reining in the pandemic. “If severe disease somehow reflects a higher level of virus, those people may be more contagious,” Mulligan says. “[By] preventing the severe cases, there might be less virus transmission, and people would be more likely to recover as opposed to die.”
Currently, severe COVID-19 is placing a huge strain on healthcare systems across the country. Earlier this month, hospitals in Los Angeles were forced to prepare to ration care as severe cases spiked. Many doctors, nurses, and other healthcare workers are struggling with burnout. Clinical trials and elective procedures for other conditions have been put on hold.
“We need to decrease the number of people getting infected, and more importantly, if somebody is going to get infected, we have to make sure that we can reduce that disease severity,” says Schultz-Cherry. “Because that’s what’s devastating about the infection, is that you can get very severe disease, especially in certain high-risk groups.”