Everything we know so far about COVID boosters


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Between efforts to get enough Americans vaccinated against COVID-19 and worries about new variants, you may be wondering if you’ll have to get a booster dose soon. Scientists and public health officials are still working to figure out who needs a booster shot right now, and whether we all will eventually.

Whether or not we will need a “booster,” or an extra vaccine dose that gives the immune system a lift against a virus, depends on a few factors, according to a June 23 presentation by a Centers for Disease Control and Prevention working group. These include the risk of waning immunity from the original doses, as well as the risk that new COVID-19 variants will mutate enough to get around the vaccines. On an individual level, your level of vulnerability to COVID-19 could also affect how soon you might need a booster.

Dr. Anthony Fauci, chief medical advisor to the president, said in an interview with PBS Tuesday that the “bottom line” when it comes to booster shots is “you keep an open mind always.” 

“I would think it was likely, at some time, we may need a booster,” Fauci said. “When that will be will be determined by the studies that are being done.”

There are studies being conducted now about booster shots, as well as whether or not the current vaccines are effective against the new and highly contagious delta variant. Current expert advice on whether boosters are necessary for delta is a bit confusing. Pfizer announced on July 9 it is at work on a booster targeting delta, prompting the CDC and Food and Drug Administration to release a joint statement the same day stating that fully vaccinated Americans don’t need one.  

While some countries move ahead with booster shot recommendations for certain people, and we sift through conflicting advice in the US, we outline everything we know so far about COVID boosters . 

Who might need a booster first?

Right now, there isn’t sufficient data for health officials in the US to recommend a booster shot to the general population. But they are monitoring the situation, particularly for certain at-risk groups. 

At the meeting on June 23 with the CDC and the Advisory Committee on Immunization Practices, members presented that there’s “no data to support recommendations for booster doses currently.” That could change, they said, if there’s evidence of declining vaccine effectiveness, or evidence that a COVID variant gets around the vaccines and significantly lowers their protection. 

“I would want greater certainty on the safety data if we’re talking about boosting before it’s clear what the risk data will look like,” ACIP Safety Chair Dr. Grace Lee said at the CDC meeting, per CNBC. “If we’re seeing severe breakthrough cases then I think the decision-making moves forward even if there’s uncertainty with the safety data.” As of May 1, the CDC only monitors breakthrough COVID-19 cases in vaccinated individuals that are severe, meaning they result in hospitalization or death.

But earlier booster shots could benefit people who are most at risk for COVID-19. At the meeting, members pointed out that immunocompromised folks, people aged 65 and older, those taking certain drugs, people recovering from cancer or an organ transplant, and those who have other conditions that suppress immunity should be monitored in their need for a booster. Health care workers should also be monitored, they said.

That’s because those with certain health conditions that suppress the immune system are less protected by the vaccine. Research from late 2020 also showed that certain health conditions make it much harder for the immunocompromised to clear COVID-19 from their body, dragging illness on. On June 23, a study in the New England Journal of Medicine found that a third shot “significantly improved” the vaccine’s effectiveness in solid organ transplant patients, who had a weak immune response to just two doses of an mRNA vaccine.

Some countries have already given the green light for boosters for people most in need. France has made the call to recommend a third COVID vaccine for the severely immunocompromised, including transplant recipients, people with certain autoimmune diseases and dialysis patients, the Boston Globe reported. On Wednesday, health officials in Britain started planning a booster shot program for the most vulnerable populations as early as September, the Guardian reported.


In other countries, COVID booster plans are in the works for certain groups. 

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There’s a chance you won’t need a booster at all

Recent findings from a study on mRNA vaccines suggest that those who got both shots of Pfizer or Moderna may have immunity for years without a booster. By the same logic, people who were infected with COVID-19 and recovered before being vaccinated may not need a booster at all, The New York Times reported. Although the study was small (scientists looked at 14 people), it offers reason to be cautiously optimistic that immunity from mRNA vaccines could offer lasting protection to the general population, with exceptions for the immunocompromised, the elderly and other vulnerable groups.

Again, though, boosters could become necessary for everyone if a new variant of the virus sidesteps the current vaccines. Fortunately, that doesn’t seem to be the case for the current “variant of concern,” the delta variant.

How the vaccines stack up against delta

Good news — all three vaccines are proving to be effective against severe disease caused by the delta variant, though the level of research on this varies vaccine to vaccine.

Research in the United Kingdom found that, though AstraZeneca’s and Pfizer’s effectiveness was slightly lowered when faced with delta compared to the earlier alpha variant, two doses of either vaccine were effective against symptomatic disease from delta — about 88% for Pfizer, and 60% for AstraZeneca. Getting only one dose showed significantly lowered protection against delta.

The UK study didn’t include Moderna (it wasn’t widely available there), but given that Moderna is also an mRNA vaccine and has a very similar efficacy rate to Pfizer, the news is promising for that vaccine, too. Additionally, preliminary data released by Moderna found that the vaccine only showed a “modest reduction” in antibodies against delta, meaning it’s still effective.

Information from Israel shows that Pfizer is less effective against COVID-19 infection from delta than previous studies found, but still highly effective at preventing severe disease. On July 5, Israel’s Ministry of Health said that Pfizer’s protection against COVID-19 infection from delta has fallen to 64%, Haaretz reported, down from 91.2% efficacy in March. The ministry said that Pfizer is 93% effective at preventing hospitalizations and severe symptoms. 

As far as Johnson & Johnson is concerned, research published on July 1 about the US’s only single-dose vaccine is promising. In a study on health care workers in South Africa who had been vaccinated with J&J, only 2% of breakthrough COVID infections were severe. Protection against severe disease is the biggest benefit of the vaccines, as this leads to fewer deaths. 

In the study’s report, co-principal investigator Professor Glenda Gray said of Johnson & Johnson: “We have mounting data to suggest that immunity increases over time and that it retains its efficacy against important variants such as beta and delta.”

Dr. Angela Rasmussen, a virologist who received a J&J vaccine herself and had urged those who also received one to consider a shot of an mRNA vaccine, said on Twitter that the latest research indicates that J&J is effective against delta, but that “we need more info about frequency of breakthrough and what they mean by immunity improving over time.” 


The three vaccine makers producing shots for the US (Moderna, Pfizer and Johnson & Johnson) are studying the effectiveness of their vaccines, and the potential for a booster. 

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What the vaccine companies are saying

Pfizer recently announced that it is developing an updated version of its vaccine that targets the delta variant. The company also said that a third shot of their original vaccine “has the potential to preserve the highest levels of protective efficacy” against all variants (including delta), citing the real-world data from Israel’s Ministry of Health that suggests protection from symptomatic infection might decline over time.

A spokesperson for J&J said that the vaccine “continues to offer durable protection, and at present there is no evidence to suggest a need for a booster dose to be administered.” They also said that the company is “confident that the efficacy of the Johnson & Johnson COVID-19 will be preserved against the delta variant.” In fact, in a press release, J&J suggested its vaccine might be more protective against delta than the beta strain (first detected in South Africa), as data shows the vaccine “elicited neutralizing antibody activity against the delta variant at an even higher level.”

Moderna didn’t immediately respond to request for comment, but in a report June 27, Moderna CEO Stephane Bancel told Barrons that he proposes “we should rather be two months too early, than two months too late” on a COVID booster. 

Can you switch vaccine companies for a booster dose?

If you do end up needing a booster, it could potentially be tricky to get one from the same company as your original doses. But if you can’t get access to the same vaccine again, is it safe to mix and match? The three vaccines offer the same effect, but deliver in different ways. Moderna and Pfizer’s COVID-19 vaccines have two-dose regimens that use a new mRNA technology, while Johnson & Johnson’s one-dose vaccine uses viral vector technology. 

Health officials in the US aren’t yet ready to make the call that mixing COVID vaccine brands is safe, but research is underway. In the UK, scientists at the University of Oxford found that mixing doses of Pfizer and AstraZeneca generated a strong immune response, BBC reported. Mixing brands for other vaccines, such as the HPV vaccine, has also been safely done.

On June 1, the National Institutes of Health started a trial that tests mixing COVID-19 vaccines, and will determine if those who got Pfizer or J&J initially can safely receive a Moderna booster. The initial results of the study are expected in late summer 2021, the NIH said in a news release.

“The results of this trial are intended to inform public health policy decisions on the potential use of mixed vaccine schedules should booster doses be indicated,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in the release.

If research proves that mixing and matching COVID-19 vaccine doses is safe, that will open doors of access for people needing a booster quickly, or those wanting a different one than the vaccine they originally received. For example, women under age 50 who first received Johnson & Johnson’s vaccine may opt for a different booster, as the CDC has warned that women under 50 should be “especially aware” of the very rare risk of blood clots affecting the group.

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What comes next 

Similar to how there was a need-based rollout system for the first rounds of COVID-19 vaccines, there will probably be a similar system in place when boosters are recommended in the US — those most at risk of severe disease from COVID-19 will get them first. While we all wait with bated breath for more direction, the best thing you can do now is make sure you’re up-to-date on your regularly scheduled COVID vaccine regimen. 

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.


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