Understanding the Debate Over Covid Booster Shots

(Bloomberg) -- With the especially contagious delta variant threatening efforts to end the pandemic, a growing number of wealthy countries are planning to or considering administering booster shots of Covid-19 vaccines, at least to particularly vulnerable groups. U.S. regulators said Sept. 22 that people 65 and over and others at high risk of severe Covid or Covid complications can receive a third dose of the Pfizer Inc.-BioNTech SE vaccine. Officials at the World Health Organization have characterized the wide rollout of boosters in wealthier countries as unethical as long as poorer countries still lack supplies to cover significant portions of their populations with initial doses. 

1. What’s a booster shot?

The term traditionally has referred to an additional dose of a vaccine given some time after the initial course of inoculation to bolster protection that may have started to wane. While many vaccines produce long-lasting immunity, the U.S. Centers for Disease Control and Prevention recommends that adults receive boosters of the tetanus vaccine every decade, for example. For Covid-19, a new disease, researchers are working out the optimal schedule and dosage for a wide variety of vaccines on the fly in the midst of an ongoing pandemic. The term booster is being used loosely to refer to additional shots given for a variety of reasons to people who have already received the prescribed course of a Covid vaccine, meaning one dose of Johnson & Johnson’s formulation or two doses of any of the others. With the messenger RNA vaccines, the first two shots were given relatively close together, either three or four weeks apart. If an additional dose is given six months or so after the first two, it may produce longer-lasting immunity, by training the immune system to realize that Covid is a long-term threat.

2. What are the reasons?

There’s a small group of people with weakened immune systems, such as transplant recipients, who are likely to need an additional shot sooner rather than later. The extra shot isn’t a traditional booster, as these people likely never get an adequate response to an initial course of Covid vaccine. For the rest of the population, an additional shot (or shots) may prove to be helpful if immunity wanes over time or if new coronavirus variants emerge that evade vaccine protection. In the first scenario, giving another dose of the original vaccine may be sufficient. That’s mostly what is being considered for the immediate future. In the second scenario, shots customized against new variants may be needed. 

3. What other countries have signed on to extra Covid shots?

Germany, France and the United Kingdom are among those that have started or decided to offer them to more vulnerable groups, such as the elderly, those over 50, or those who are immunocompromised. Offering them more broadly to people months after their last dose are Israel, Russia, Hungary and the United Arab Emirates. Some countries plan to give extra shots using a vaccine type that’s different from the one people got initially. For example, Chile announced plans to offer booster shots from AstraZeneca Plc to people 55 and older who earlier received the vaccine from Sinovac Biotech Ltd. This mix-and-match strategy is called a heterologous boost, and there’s some evidence it can provide an advantage over an additional dose of the same formulation.

4. What’s motivated the move to boosters?

The rise of the delta strain, combined with some preliminary data suggesting that Covid vaccine effectiveness may decline relatively quickly, has intensified the focus on booster shots. In Mesa County, Colorado, where delta took off earlier than in other parts of the state, a study by state health officials found that vaccines were 78% effective in a two-week period ending June 5, versus 89% in other counties. And an observational study from Israel, one of the first countries to vaccinate most of its population, suggested that a third dose of the Pfizer-BioNTech shot dramatically boosted protection in people 60 and over, at least in the short term. According to the data published in the New England Journal of Medicine, confirmed infection rates were 11 times lower in the booster group compared to those who had only gotten the standard two doses starting 12 days after the third dose. A separate analysis of data from the final-stage trial of the Pfizer-BioNTech vaccine showed that efficacy eased to about 84% at the end of a six-month period compared with 96% early on.

5. Is everything pointing toward a need for boosters?

No. Moderna Inc. said on Aug. 5 that data from its final-stage trial showed its vaccine remained 93% effective through six months, just one percentage point less than the initial shorter term results. (Moderna does say it expects protection to wane over time, and it has applied for emergency clearance in the U.S. for a third shot.) A U.K. study published in the New England Journal of Medicine in July found that the Pfizer-BioNTech vaccine was 88% protective against symptomatic cases of the delta variant, while AstraZeneca’s vaccine was 67% effective. In September, a published analysis of data from 21 US hospitals in 18 states found that while the Pfizer-BioNTech vaccine declined in protection against hospitalization after about four months, protection from Moderna’s shot remained stable. 

6. How are decisions about boosters made?

It’s a judgment call by public health officials, since there’s no scientific consensus for when booster shots become necessary. In the U.S., the Food and Drug Administration official in charge of vaccine regulation, Peter Marks, has said that the U.S. doesn’t have a “predetermined minimum” for how much efficacy must fade before it authorizes booster shots. 

7. What are the objections?

“It would be unconscionable to offer people already fully vaccinated another dose before protecting people who haven’t been vaccinated at all,” the global nonprofit Doctors Without Borders said in a July 22 statement. Epidemiologists warn that allowing the coronavirus to continue to run rampant in some parts of the world increases the odds that more dangerous variants will arise. Those new variants may make their way across the globe and prolong the pandemic. Drug companies with a financial interest in selling more doses have been some of the loudest voices talking up the need for boosters. And Covid vaccines seem to be holding up well in achieving their key goals -- preventing severe disease, hospitalization and death -- even if they aren’t quite as effective at blocking milder cases of symptomatic infection with delta. In the U.S., for example, as of Sept. 13, only about 15,800 patients with Covid vaccine breakthrough infections had been hospitalized or died, a tiny fraction of the total hospitalizations and deaths, according to the CDC. 

8. Is it possible to expand the vaccine supply?

White House spokeswoman Jennifer Psaki has called the WHO’s position that rich countries should put boosters on hold until poor countries vaccinate more of their population a “false choice.” The U.S. can both donate vaccines abroad and provide boosters domestically if regulators recommend them, she said Aug. 4. But in reality, the Covid vaccine supply is limited, and wealthier countries have bought up a hugely disproportionate share of the available shots. In September, Covax, the global program to immunize the world against Covid, cut its 2021 supply forecast by 25%, citing hurdles in production and other constraints. The 5.95 billion doses given as of Sept. 19 is only enough to fully vaccinate just under 38.7% of the world population, according to the Bloomberg Vaccine Tracker. Countries and regions with the highest incomes are getting vaccinated more than 20 times faster than those with the lowest. At the current rate of giving shots, it will take six months to cover 75% of the world population, according to the tracker.

The Reference Shelf

• Related QuickTakes on delta, how well vaccines are working, breakthrough Covid, herd immunity and vaccine mixing.
• Bloomberg News details the months of internal debate over boosters between political appointees and health and science officials in the Biden administration.
• Bloomberg Opinion’s Faye Flam argues that it’s not yet the time for boosters, while Max Nisan argues that a big push for them would be wrong and dangerous.
• The U.S. CDC explains how vaccines work.

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