The best way to avoid new Covid variants is to delay booster shots

Walmart pharmacist holds a vial of the Moderna coronavirus disease (COVID-19) vaccine inside a Walmart department store in West Haven, Connecticut, U.S., February 17, 2021.
Walmart pharmacist holds a vial of the Moderna coronavirus disease (COVID-19) vaccine inside a Walmart department store in West Haven, Connecticut, U.S., February 17, 2021.
Image: Reuters/Mike Segar
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As the delta variant makes breakthrough infections of Covid-19 more common, countries that include the US, the UK, Denmark, France, Germany, Greece, Spain, and Israel are at various stages of rolling out booster shots for vaccinated people.

The hope is that booster shots might offer added protection against the virus. But some scientists say that right now, the best protection against delta and other variants isn’t prioritizing booster shots, but making sure that everyone in the world has the opportunity to get their first doses.

“If you want to change the arc of the pandemic, vaccinate people who are unvaccinated,” says Paul Offit, a pediatrician specializing in infectious diseases at the Children’s Hospital of Philadelphia, who is also a member of a Food and Drug Administration (FDA) advisory committee on vaccines.

Booster shots versus global vaccine equity

The World Health Organization (WHO) has called for wealthy countries to put off distributing booster shots through the end of the year, in the interest of getting vaccine supplies to people in low-income nations. “Because manufacturers have prioritized or been legally obliged to fulfill bilateral deals with rich countries willing to pay top dollar, low-income countries have been deprived of the tools to protect their people,” WHO director-general Tedros Adhanom Ghebreyesus said last week.

US surgeon general Vivek Murthy, however, argues that getting booster shots to Americans and distributing vaccines to poorer countries aren’t mutually exclusive endeavors. “We clearly see our responsibility to both, and that we’ve got to do everything we can to protect people here at home while recognizing that tamping down the pandemic across the world and getting people vaccinated is going to be key to preventing the rise of future variants,” Murthy said on Aug. 19.

It’s true that the US has already donated 115 million vaccine doses worldwide, with plans to distribute 500 million more. But it’s also true that vaccine supplies are currently limited due to insufficient manufacturing capacity. For now, distributing booster shots on a national scale will inevitably leave fewer doses available to be shipped to other countries.

And many countries are desperately in need. Only 2% of people in low-income countries have received at least one dose, according to a recent estimate from Our World in Data, which collects statistics from global governments and health ministries. By comparison, 66% of people in high-income countries have had at least one dose.

Vaccine inequity is bad for wealthy countries, too

That gap is problematic from a global vaccine equity standpoint, but it’s also bad news for vaccinated people. “Until we get the world vaccinated, the pandemic will be prolonged,” says Anna Durbin, a professor and infectious disease specialist at Johns Hopkins Bloomberg School of Public Health. One big concern is that “as long as you have naive populations that can spread and transmit the virus, you’re going to see new variants emerge.”

New Covid variants can easily cross national borders, which means any strain that emerges in a poorer country where fewer people are vaccinated poses a threat to inhabitants of wealthy countries, too.

The delta variant, which is twice as contagious as previous strains, has already offered a terrible demonstration of how important it is to limit the virus’s opportunities to mutate. And while unvaccinated people are far more vulnerable to delta than vaccinated people, the variant has impacted both groups. Delta has many parents worried about the safety of kids too young to receive jabs, and breakthrough infections—however limited our understanding of them—show that future variants could be even more adept at overcoming the body’s defenses.

A worst-case scenario would be the emergence of variants that are resistant to Covid-19 vaccines entirely, “where it’s almost like a new virus and our immune system may not recognize it as readily,” Durbin says.

Thankfully, chances of that happening are low—but it’s a possibility everyone wants to avoid, and one that highlights the stakes of mass vaccination.  ”A more vaccinated world creates a more hostile global environment for SARS-CoV-2,” explains Katherine J. Wu in The Atlantic. “Mutations will still occur, but fewer of them will be of consequence; lineages will still splinter, but they’ll do so less often.”

Do booster shots make a big difference?

Another reason to put global vaccine distribution ahead of booster shots, according to Offit at the Children’s Hospital of Philadelphia: There’s not a ton of evidence supporting the idea that booster shots offer significantly greater protection against severe illness than two doses.

Offit says that so far the vaccines seem to be doing what they’re supposed to do: protecting against hospitalization and death. That’s true despite the fact that the delta variant has led to an uptick in breakthrough Covid cases in vaccinated people. He points to this summer’s Provincetown, Massachusetts outbreak, in which a striking 74% (346) of 469 people diagnosed with Covid-19 were vaccinated, but only four of the 346 people were hospitalized. “The hospitalization rate was 1.2%, which means the vaccine was doing its job,” Offit says.

As long as vaccines are preventing people from getting severely ill, Offit says there’s not a strong reason to think that a booster shot would make people much safer. An international group of scientists made similar points in an opinion piece published in the journal The Lancet Monday, saying that their review of recent studies shows that while “the efficacy of most vaccines against symptomatic disease is somewhat less for the delta variant than for the alpha variant, there is still high vaccine efficacy against both symptomatic and severe disease due to the delta variant.” (The calculus is different when it comes to immunocompromised people, who make up about 3% of the US population, and who have already been authorized by the FDA to receive a third dose.)

Complicating our understanding of booster shots is the fact that we’re still learning how long immunity from vaccination lasts. A new analysis from Pfizer, released by the FDA and based on data coming out of Israel and the US, found that the vaccines’ protection against severe cases could “eventually follow observed reductions in effectiveness against” breakthrough infections in general. The FDA will discuss Pfizer’s new data, as well as its own forthcoming report on booster shots, at a public meeting on Sept. 17.

Reducing the risk of new variants

In the long term, booster shots may well be necessary. Durbin says the “when” depends in part on how long it takes for the world to reach sufficient immunity, via a combination of vaccination and natural infections, so that Covid poses less of a threat to our bodies and is more comparable to a common cold. It may also turn out that certain vulnerable demographics will need booster shots earlier than the general population.

“Eventually this will be a three-dose vaccine,” Offit predicts. “I think that’s right. The question is, does it need to be a three-dose vaccine right now?”

Based on the currently available information, the most impactful way for wealthy countries to protect the health of all people—including their own citizens—is to pour more resources into revving up vaccine production and worldwide distribution. “It’s not just an equity issue,” says Durbin. “It helps protect the world and get us out of Covid at a much faster pace.”