How do COVID infections differ in vaccinated vs. unvaccinated people? What to know

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The coronavirus is running rampant again in the U.S., thanks to more dangerous coronavirus variants, which health experts say are fueled mostly by people who refuse to get vaccinated against COVID-19.

The nation’s seven-day average for new cases jumped 44% from the previous week, hospitalizations increased by 41%, and deaths surged 26%.

To be clear, infections are occurring in both unvaccinated and vaccinated people, but to a much lesser extent in the latter group. That’s because the vaccines have proven effective even against the delta variant, which is more contagious and may cause more severe disease.

According to Centers for Disease Control and Prevention national estimates, people who are vaccinated benefit from an 8-fold lower risk of developing COVID-19 once infected and a 25-fold lower risk of hospitalization and death. (There’s a difference between just getting infected and going on to develop the disease the coronavirus causes.)

On an individual level, risk of severe disease or death is reduced 10-fold or greater in vaccinated people, while risk of infection is reduced 3-fold.

While vaccination status certainly determines how one’s infection plays out, other factors, such as duration of exposure to the virus and proximity to sick people, can affect how severe or mild someone’s case is.

Not to mention, infection with a more transmissible variant can complicate things, including the data that guide public health recommendations as a fourth wave looms.

Here’s what the most up-to-date studies show about how infections differ in vaccinated and unvaccinated people.

Symptoms are milder and shorter-lived in vaccinated people

A CDC study using data collected before the delta variant became the dominant version of the coronavirus in the U.S. found that fully or partially vaccinated people had about a 60% lower risk of developing symptoms, such as fever or chills, compared to the unvaccinated when infected.

Some of the nearly 4,000 health care workers in the study who were vaccinated didn’t develop symptoms at all.

If they did, symptoms were shorter-lived — about 10 days long compared to about 17 days for the unvaccinated. That includes an average of two fewer sick days in bed.

The data confirms the vaccines are doing “exactly what they were supposed to do: prevent severe disease, hospitalization and death,” CDC Director Dr. Rochelle Walensky said during a White House COVID-19 briefing on Monday.

As of July 26, when more than 163 million people in the U.S. had been fully vaccinated, the CDC reported 6,587 people with breakthrough infections among the vaccinated who were sick enough to die or be hospitalized.

A total of 1,293 of them have died. That’s less than 0.001% of those who had been fully vaccinated at the time.

Infections in the vaccinated are likely less transmissible

Because symptoms are milder and tend to go away faster in vaccinated people, experts say this suggests they are less likely to spread the virus to others; less coughing or sneezing means fewer opportunities for the virus to latch onto others.

The delta variant, however, has challenged this idea (more on this below).

Viral load, or the amount of virus particles someone carries in their upper airways, is also 40% lower in infected fully or partially vaccinated people, the CDC study found, with the virus being detected for six fewer days in their respiratory samples compared to infected unvaccinated people.

Vaccinated people were also 66% less likely to test positive for the virus for more than one week compared to the unvaccinated.

“While these indicators are not a direct measure of a person’s ability to spread the virus,” the agency said, “they have been correlated with reduced spread of other viruses, such as varicella and influenza.”

Delta variant raises viral load, disease severity and risk of infection

The most recent data shows the delta variant is more transmissible than the common cold, smallpox, Ebola, influenza and the 1918 “Spanish” flu, according to the CDC, and that it is as transmissible as chicken pox.

Walensky said people infected with the delta variant can spread the virus to more than double the number of people than those infected with the previously dominant alpha variant.

Part of the reason is that the variant arms people with more virus particles in their noses and throats.

A study from China found that the viral load in delta-infected people was about 1,000 times higher than in people infected with the original version of the coronavirus.

And despite vaccination status, age or other health conditions, the delta variant still presented a 120% higher risk of hospitalization, 287% higher risk of intensive care unit admission, and 137% higher risk of death, according to a study from Canada.

Another paper from Singapore found that the delta variant increases infected people’s risk of needing supplemental oxygen and nearly doubles the risk of coronavirus-related pneumonia.

So, is vaccination even worth it as delta spreads?

Yes, health experts say, because without protection from vaccination, people are at the mercy of the delta variant.

“People should be reassured that if they are fully vaccinated that they are very likely, highly likely, to be protected against severe or critical illness, the kind of illness that would cause them to be hospitalized or killed by this virus,” Dr. Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, told The Washington Post. “Vaccines save your life.”

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