Boosters provide excellent protection against omicron, new data confirms. Which one to choose ?

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For the latest news and information on the coronavirus pandemic, visit the WHO and CDC websites.

Although the definition of “fully vaccinated” has not changed, you are not considered “up to date” by the United States Centers for Disease Control and Prevention until you receive your COVID-19 reminder (when you are eligible). Indeed, growing evidence shows that boosters are needed to restore protection against the new omicron variant, which has reduced the effectiveness of vaccines against COVID-19 infection.

However, two reports released Friday by the CDC revealed good news about how our boosters are holding up to omicron and how vaccines continue to protect against hospitalizations caused by COVID-19. When the omicron variant first appeared in the United States, adults given a booster shot were five times less likely to be infected than unvaccinated adults. Third doses or boosters from Pfizer or Moderna were also 90% effective in preventing hospitalization with COVID-19 when omicron emerged, the CDC found.

Anyone 12 years of age or older is eligible for a booster. Recently, the CDC even shortened the period a person who received the vaccine from Pfizer or Moderna must wait for a booster, up to five months instead of six. (People who received the Johnson & Johnson vaccine should still receive a booster at least two months after their single-dose vaccine.)

The booster recommendation is clear now (get one), but the advice leaves you with a bit of choice. While the CDC has recommended that everyone get a booster dose of the vaccine from Pfizer or Moderna (the mRNA vaccine is preferred over Johnson & Johnson in most cases, according to the CDC, even if you initially received the J&J). That’s because people are now able to “mix and match” COVID-19 vaccines after heterologous booster doses were authorized by the US Food and Drug Administration.

As the world continues to monitor the coronavirus and scientists adjust information accordingly, here’s what to know about choosing a booster.


CDC data shows that in December, unvaccinated adults ages 50 to 64 were 44 times more likely to be hospitalized with COVID-19 than fully vaccinated and boosted adults. The risk was even higher, 49 times, for adults 65 or older compared to the same age group who had been boosted.

US Centers for Disease Control and Prevention/Screenshot from January 21

How are COVID-19 vaccines different?

Although all three vaccines have the same effect – protection against severe COVID-19 disease – the way they work is a bit different. Pfizer and Moderna are mRNA vaccines, which teach our cells to make a specific protein and build immunity against a virus. Johnson & Johnson (the only authorized single-dose vaccine) is a viral vector, which uses a harmless virus to activate an immune response that teaches our bodies what to fight against in future infections.

Both types of vaccines prepare our immune system for COVID-19 infection and none of the coronavirus vaccines infects us with the real coronavirus. Pfizer’s and Johnson & Johnson’s boosters are the same dose as the original vaccines, while Moderna’s booster is half the size of its original vaccine.

After an outside committee advising the CDC raised concerns about a rare but sometimes fatal blood clotting disorder this can happen after vaccination with the Johnson & Johnson vaccine, the CDC recommends people get the vaccine or booster from Pfizer or Moderna instead. However, Johnson & Johnson’s vaccine is still licensed and available to people 18 and older if they prefer it.

Does mixing and matching work?

Research currently available in the United States as well as other countries shows that choosing a different COVID-19 vaccine as a booster is effective. In some cases, mixing and matching seems to produce a stronger response compared to sticking to the original vaccine.

In a mixed COVID-19 vaccine trial funded by the National Institute of Allergy and Infectious Diseases (before omicron was the dominant variant), boosters from all three vaccine companies induced good immune responses in about 450 people who received different vaccines. In the study, Moderna’s booster gave the most robust response. However, this study looked at a full dose of Moderna, rather than the company’s authorized half-dose recall, which may minimize Moderna’s advantage over Pfizer, as reported by The Atlantic.

Another preliminary study involving 64 people found that people who initially received the Pfizer vaccine, but then received a booster vaccine from Johnson & Johnson, had a stronger response to the Johnson & Johnson vaccine. This included the harder-to-measure T-cell immune responses that Johnson & Johnson’s vaccine appears to protect as opposed to the antibody response alone – which Johnson & Johnson says could be the reason two doses of his vaccine provide great protection against hospitalization and illnesses caused by the omicron variant.

An earlier Spanish study published in the journal Nature in May 2021 found that mixing a dose of AstraZeneca (a similar vaccine to Johnson & Johnson) with a dose of Pfizer produced a higher antibody response than people who receive two doses of AstraZeneca. However, it is unclear whether this group had a higher immune response than people who received two doses of Pfizer.


The definition of “fully vaccinated” has not changed. A person is considered fully immunized two weeks after their second dose of Pfizer or Moderna, or two weeks after a single dose of Johnson & Johnson.

Sarah Tew/CNET

Which booster injection should I receive?

Regardless of which COVID-19 vaccine you originally received (Pfizer, Moderna, or Johnson & Johnson), you should receive a vaccine booster from Moderna or Pfizer, according to the CDC. However, children and adolescents between the ages of 12 and 17 should receive a Pfizer booster, as Pfizer is the only COVID-19 vaccine authorized for people under the age of 18.

The preference for one or the other mRNA vaccine followed concerns about a rare but serious blood clotting disorder associated with Johnson & Johnson’s vaccine, called thrombosis with thrombocytopenia syndrome. Since the CDC suspended distribution of the disorder to investigate, more information has revealed that it is less rare than previously thought and occurs in both men and women. (Although still rare overall, occurring in 57 cases out of 16.9 million doses of Johnson & Johnson administered, according to the CDC, women between the ages of 30 and 49 are at higher risk of developing this disorder, about 1 woman out of 100,000 by being a victim). Nine people have died from TTS and all cases required hospitalization or intensive care admission, according to a CDC presentation.

The Johnson & Johnson vaccine is available to you if you prefer it for some reason, or if you cannot take the Moderna or Pfizer vaccine due to an allergy. But given the excellent safety and wide availability of Pfizer’s and Moderna’s vaccines, the CDC made the recommendation consistent with what other countries have done for AstraZeneca’s vaccine, which is associated with the same rare problem.

A study published by the CDC in September (before omicron) compared the effectiveness of the vaccine in the real world found that two doses of Moderna’s vaccine were 93% effective in preventing hospitalization, two doses of Pfizer were effective at 88% and a dose of Johnson & Johnson was 71% effective. And although omicron eludes our protection against COVID-19 infection given by vaccines, some protection against serious disease remains.

According to booster dose data collected by the CDC, most people who received the vaccine from Pfizer or Moderna appear to stick with their original brand of vaccine (most people who received the vaccine from Johnson & Johnson originally received a different recall). However, millions of Americans have opted for a different brand of vaccine as a booster, and no safety concerns have been raised by the FDA or CDC in people who have mixed and matched.

Are you fully vaccinated after your booster?

Importantly, the definition of fully vaccinated has not changed (although it may happen in the future). You are still fully vaccinated two weeks after your second Pfizer or Moderna injection or two weeks after your Johnson & Johnson vaccine. The fact that a person has received a booster does not affect their “fully vaccinated” status.

Can I mix and match the first two plans?

No, the CDC’s statement on mixing COVID-19 vaccines only applies to recalls. For now, the FDA has only authorized a mixed-series booster, which means the first round of coronavirus vaccines must be one dose of Johnson & Johnson or two doses of Moderna or Pfizer.

Once mixed round boosters begin to roll out in greater numbers to Americans, there will be more data on the safety and effectiveness of a mixed round of COVID-19. While it may be too early to hope, this could mean that data on the mix for boosters will inform decisions on which primary coronavirus vaccine series are used together, making it easier to reach underserved communities. and eventually reduce health care and vaccine inequities.

The information in this article is for educational and informational purposes only and is not intended to constitute medical or health advice. Always consult a physician or other qualified health care provider with any questions you may have about a medical condition or health goals.

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