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How Vaccines Protect Communities


People who’ve had the opportunity to be vaccinated so far are understandably feeling relief that they’re better protected. But even for someone who’s still patiently (or impatiently) waiting for the COVID-19 vaccine to become available, the rollout of vaccines to anyone in their community is still good news.

We talked to several Penn Medicine experts to learn more about how and why vaccines protect the communities we live in as a whole, even as we work to get more people vaccinated to reach herd immunity.

How much do we know about how well the vaccines can prevent infection and prevent transmission to others?

Most of the initial news stories and other information rightly centered on how effective a vaccine was at protecting the person who received it. That’s what those first studies were designed to do. Take the Moderna and Pfizer/BioNTech vaccines, for example, authorized by the U.S. Food and Drug Administration for emergency use and developed based on mRNA research from the lab of Drew Weissman, MD, PhD, a professor of Infectious Diseases in Penn’s Perelman School of Medicine, along with Katalin Karikó, PhD, an adjunct associate professor.

The Moderna vaccine holds a 94.1 percent efficacy at preventing symptomatic COVID-19 after the second dose. The Pfizer vaccine is 95 percent (efficacy refers to the performance of something in a controlled setting, whereas effectiveness refers to its performance in the “real world”). The latest vaccine from Johnson & Johnson, a one-shot vaccine approved by the FDA for emergency use on Feb. 28, holds an 85 percent protection against severe COVID-19 – and studies showed it prevents 100 percent of hospitalizations and death from the virus. Again, those initial percentages reflect how well it protects people from falling ill, not how effective it is at preventing an infection of the virus or spreading it to others. It wasn’t known at that time because they hadn’t measured it initially.

That’s changing, though, as data starts to come in. “Some studies are pointing in a very favorable direction,” Anthony Fauci, MD, the White House COVID-19 Response Team’s chief medical adviser, said during a White House briefing recently.

For example, a study from the University of Oxford suggests that the Oxford-AstraZeneca vaccine appears to substantially reduce transmission of the virus. The researchers found that the vaccine had decreased the number of positive tests among individuals by 67 percent. Another study found that two doses of the Pfizer vaccine reduced the chances of an infection that could be passed along by 86 percent.

Why do we still need to wear a mask and continue social distancing after being vaccinated?

Going off initial reports like the above studies and what’s known about vaccines in general, experts believe the COVID-19 vaccinations likely offer up protection to others. However, the limited amount of information on how effective they really are at stopping the spread means people still need to stay diligent.

It’s possible, researchers have said, that a vaccinated person with immune protection could still be shedding the virus and potentially infect others. The virus could be living in the respiratory tract or other places.

That’s why people still need to wear a mask and continue to practice social distancing.

The vaccine also holds the most promise due to the lack of effective treatments for COVID-19. Doctors possess limited tools to fight severely illness in patients who end up in the hospital, making the vaccine still the sharpest one.

Is my household overall safer if one household member got the vaccine but others are still waiting?

Because of the lack of data on the vaccines, it’s hard to know for sure, said Stephen Gluckman, MD, an infectious disease doctor at Penn Medicine, but he expects it reduces the risk to a degree.

“It’s likely the vaccine is preventing transmissions, so whatever that is adds to some safety in the household,” he said. “However, one shouldn’t rely entirely on the vaccine, where they neglect the tried-and-true methods of prevention, which are masks and distancing. When talking about vaccines, it’s important to not lose sight of what we know works now.”

Even people who have been vaccinated, including one sharing a household with non-vaccinated people, he added, should act as if they haven’t been to ensure they’re protecting others.

How else do vaccines protect communities?

The implications from COVID-19 go far beyond the medical. The pandemic left the U.S. in significant economic downturn and pushed millions of Americans out of their jobs. Businesses continue to close. Education has suffered. Travel has dropped sharply.

“It is unequivocally a social and economic issue,” Gluckman said. “When you look at so many people who have lost their jobs, their houses — they’re really struggling. That is a direct effect of COVID.”

Vaccinations will help put the economy on the road to recovery more quickly and help repair communities hit so heavily.

How can vaccination better protect communities in an equitable way?

Access to the COVID-19 vaccination plays another important role in protecting communities, particularly ones hit hardest by the pandemic, such as minority and vulnerable populations.

The disparity is wide: Despite being infected and dying at a higher rate, Black people are receiving vaccinations at a rate two to three times lower than white people in the U.S., according to a recent Kaiser Health News analysis.

“We need to ensure fair allocation if we want to protect our communities, not just bubbles,” said Michael Z. Levy, PhD, an associate professor of Epidemiology in the Perelman School of Medicine.

Efforts in Philadelphia and around the country continue to improve, as vaccine supply increases and more emphasis is placed on vulnerable populations. Penn Medicine and Mercy Catholic Medical Center – Mercy Philadelphia Campus came together in February with a coalition of faith and community leaders from West and Southwest Philadelphia to hold two mass vaccination clinics for community members at the Church of Christian Compassion and the Francis Myers Recreation Center. More than 1,300 people were vaccinated, with several more events planned in the future.

“We have turned our church into a hospital today,” said Pastor W. L. Herndon of the Church of Christian Compassion on a Facebook Live broadcast during the clinic. “There are some people who wouldn’t go to a place other than a place that they trust,” he said, recounting a conversation he had with a 78-year-old woman who had gotten vaccinated who hadn’t hugged or touched her children in nearly a year due to the pandemic. “That’s why this matters.”

Organizers aim to surpass the vaccination numbers from the first two events at a third clinic this weekend at the School of the Future on Parkside Avenue.

How have historical outbreaks and vaccination efforts protected communities?

Back in the 1940s, during a smallpox outbreak in New York City, intense worry over becoming infected or one’s children becoming infected, along with an aggressive vaccination campaign and rollout, led to more than 6 million adults and children vaccinated in just under a month, with only 12 infections and two deaths reported.

And when news of rising polio cases gripped the nation in the mid-1950s and virologist Jonas Salk, MD, announced over the radio a new vaccine to combat it, parents were eager to vaccinate their children from the debilitating disease former President Franklin D. Roosevelt had contracted three decades prior.

“Polio was terrifying to parents,” said Gluckman, who took part in a polio vaccine clinical trial when he was 7 years old. “Summers were over, in a sense. Swimming pools were closed. Kids weren’t allowed to play together. I suspect more kids got the vaccine because their parents were nervous, not because their parents thinking it was good for the public — even though it was.”

Widespread vaccination brought the cases down from about 30,000 in 1955 to about 1,000 by the early 1960s. By 1979, polio was considered eradicated in the United States.

History — even recent history — can also show us what happens when populations slide backwards with vaccinations. For the first time in 20 years, measles infections jumped to more than 600 cases in 2014, with nearly 150 of them linked back to a Disneyland outbreak. Many of the children had not been vaccinated by their parents or guardians because they felt vaccines were not safe.

In 2019, the number of cases hit an even higher record, at nearly 1,300. What started as small outbreaks grew into a much larger problem that began impacting an increasing number of communities, as the infection spread from one unvaccinated person to the next.

Not vaccinating yourself or your children puts the rest of society at high risk, Gluckman said at the time.

What about vaccinating children and safety from COVID-19 in schools?

The Biden Administration aims to get children back into the classroom safely within 100 days. A vaccine for children isn’t likely to be available by then, but trials are currently underway in children between the ages of 12 and 17 to test both their safety and efficacy. Johnson & Johnson also recently announced it will begin vaccine clinical trials in infants and newborns, along with pregnant women and people with compromised immune systems.

In addition to those trials, researchers are also working to better understand what level of vaccination needs to be reached to ensure better protection and less spread, as schools plan their re-openings. That’s important to know because just vaccinating adults likely isn’t enough to reach the ultimate goal of ending the pandemic.  

“Children are part of the equation,” said Levy, who historically investigates vector-borne diseases but, like so many researchers, has found himself heavily focused on SARS-CoV-2. “If we want to understand the course of the virus and variants in the future we need to better understand transmission, and the effect of the vaccine on transmission, among kids.”

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