Worried About the COVID Delta Variant? Experts Explain Risk of Breakthrough Infections to the Vaccinated

Breakthrough infections of the Delta variant are increasing.

As breakthrough infections are on the rise from the highly contagious Delta strain of the coronavirus, the precise risk to fully vaccinated individuals can be confusing.

Northwestern Medicine experts explain why the Delta strain’s breakthrough infections are on the rise, who’s at risk, and why you may need to take extra precautions depending on your age.

Who Gets Breakthrough Infections?

dr. Robert Murphy: “The vaccine is about 90% effective against the Delta variant, so one person in 10 vaccinated and exposed to SARS-CoV-2 will get a breakthrough infection. Everyone is at risk, not just the immunocompromised. They are athletes. They are perfectly healthy people. Certainly, the immunocompromised people are at higher risk because they cannot mount a strong enough immune response to the vaccine. Older people may also have a weaker response to the vaccine.

“The end game is that most people who get breakthrough infections either have very mild symptoms or have no symptoms. They rarely end up in the hospital and don’t die.

“The big question is how contagious are they? We are trying to find that out.”

Murphy is along with Drs. Chad Achenbach and Claudia Hawkins in a study with the University of Illinois at Champaign and Johns Hopkins on the infectiousness of vaccinated students who developed COVID-19 infections. Results are expected in the next one to two months.

Will we see more breakthrough infections of the Delta variant?

Carnethon: “We are seeing breakthrough infections and while we know that no vaccine is 100% effective, it feels scary. However, infections will occur and the reassuring thing is that most breakthrough infections do not cause serious illness and death. We’re not sure why the number of infections – both new and breakthrough – seems to be on the rise.

“One concern is that the Delta variant evades the vaccines. Another concern is that any virus that causes a high viral load would breach vaccine protection — and there is some evidence that the delta variant causes higher viral loads earlier in the course of infection. We will never get away from these concerns because the virus will continue to mutate itself into new variants as long as it circulates among the population, and the greatest room it has to circulate is among the unvaccinated.”

Do we need to change our behavior now that the Delta variant is the main source of breakthrough infections?

dr. Benjamin Singer: “In places with high vaccination coverage and low community transmission, you don’t have to change your behavior. Of course, vaccinated people can still choose to wear masks if they or someone in their household is at particularly high risk.

“But in places with low vaccination coverage and high community transmission, I think it makes sense to add masking when you’re indoors as an extra layer of protection against a more contagious strain.

“Delta is a more contagious variant than previous SARS-CoV-2 variants and has a weak ability to evade vaccine immunity, at least in those only partially vaccinated with one dose of an mRNA vaccine. Therefore, breakthrough infections may be more common in Delta.”

Mercedes Carnethon: “The Delta variant will not change my behavior in a community where test positivity remains low, indicating low community transfer. At this point, however, I wouldn’t choose to travel to a hotspot. But if I had to go, I’d wear my mask and try to avoid crowds of people. I would not take unvaccinated relatives to a current hot spot or relatives who have been vaccinated but remain vulnerable due to age or other conditions.

“I follow local guidelines regarding wearing masks and so feel comfortable inside without a mask. The reason I haven’t returned to wearing masks indoors in public areas is because breakthrough infections have been minimally symptomatic or asymptomatic for the most part.

“If we have hit a wall in encouraging adults to vaccinate, then as a society we need to change our mindset to treat this as another endemic virus that will infect people every year, just like the other coronaviruses that cause colds. every year. When a virus becomes endemic and infects and re-infects people over time, it becomes less virulent over time. The number of unvaccinated people who are now in hospital with this new variant shows that it is not yet mild and harmless.”

“Nevertheless, it is not sustainable to operate under the same fear level as last spring. Nor is it necessary if we have significant evidence that most of the vaccinated individuals who contract the disease recover. There are still unknowns about long-term risks of infection or long-term COVID, but I personally can’t handle that level of worry and fear about strangers. I suspect many adults feel the same way. I’ve taken all necessary precautions, but I won’t do stupid things like walking around a hot place indoors without a mask.”

Should your behavior change when you are an older adult?

Carnethon: “All vulnerable individuals, whether because of their age or pre-existing conditions, should take precautions because if they become infected or re-infected, it may not be a mild disease. The highest death rates are consistently older adults, traditionally defined as age 65 and older. However, the risks of serious illness increase with each decade of life and there is no age limit where the risk of illness is significantly lower. There are 40-year-olds with health profiles that we know are associated with serious diseases: obesity, diabetes, uncontrolled hypertension, cancer or pre-existing heart disease. These individuals, regardless of age, are just as vulnerable as older adults and should also take precautions.”

About the experts

dr. Robert Murphy is executive director of the Institute for Global Health at Northwestern University Feinberg School of Medicine.

Mercedes Carnethon, vice president of preventive medicine at Feinberg.

dr. Benjamin Singer, assistant professor of medicine in pulmonary and intensive care at Feinberg.