Which booster should I get? What you should know about mixing COVID vaccines

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Which COVID-19 vaccine should you choose for your second booster shot? It’s a question again – Pfizer or Moderna? – after the US Centers for Disease Control and Prevention agreed second booster dose of both vaccines for all adults 50 years and older, people with a weakened immune system (12 years and older) and those who have received two Johnson & Johnson syringes. If you are eligible, you can get a second booster shot four months after your last shot.

Months ago, the CDC and the US Food and Drug Administration approved the use of heterologous booster dosesor a “mix-and-match” approach to COVID-19 boosters, meaning people aren’t married to the COVID-19 vaccine they originally received.

In addition, both are mRNA vaccines (Pfizer and Moderna). recommended over Johnson & Johnson vaccine. The single-dose vaccine is associated with very rare but serious side effects (not seen with Pfizer’s or Moderna’s vaccines) and may also offer less protection from COVID-19 emergency departments, according to a CDC report published Tuesday. Because of this, most people should choose either an mRNA vaccine for a booster shot or a first shot, the agency says. But which one?

Children and adolescents aged 12 to 17 are only eligible for a booster dose of the Pfizer/BioNTech vaccine as this is the only vaccine available approved for younger age groups. But for everyone else, US public health guidance is a little less clear, raising questions about the differences between vaccines.

Here’s what we know about mixing and matching COVID-19 vaccines.

What is the difference between the Pfizer and Moderna booster?

The booster dose from Pfizer and BioNTech is the same size as the original vaccine, which is 30 micrograms. While Moderna’s booster dose is half the size of the doses administered as the first two shots, it’s slightly larger at 50 micrograms. Both are mRNA vaccines that teach our cells to make a specific protein and build immunity to a virus.

The booster shot and the Johnson & Johnson vaccine have the same dose. It is a viral vector vaccine uses a harmless virus to activate an immune response that teaches our body what to fight against in future infections.

Continue reading: I am eligible for a second admission. should i get it now


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Why mix and match?

Mixing COVID-19 vaccines when you choose a different booster shot may enhance the immune response that National Health Institute says, and it also allows for more flexibility when people make an appointment to get vaccinated or look for a shot. Other countries have allowed people to mix shots for their primary COVID-19 vaccine series.

“The most important reason is that mixing offers benefits in an enhanced immune response and therefore expects improved protection,” said Dr. William Schaffner, professor of preventive medicine at Vanderbilt University, told the UK health site Patiently. However, he added that the benefit of mixing two mRNA vaccines (Pfizer and Moderna) is less than the benefit someone who originally received Johnson & Johnson would get from an mRNA booster.

the CDC report A study published this week found that people who received two doses of Johnson & Johnson’s vaccine were less protected from emergency room or urgent care visits due to COVID-19 disease (54% effective) than people who received one dose of Johnson & Johnson followed by another received mRNA boosters (79% effective). People who received three doses of an mRNA vaccine were 83% protected from emergency visits.

Based on the new data, adults received two cans of the Johnson & Johnson vaccine are among the group of people who may receive another booster shot of either Pfizer or Moderna, the CDC said says.

During a mix-and-match COVID-19 vaccine study funded by the National Institute of Allergy and Infectious Diseases (before omicron was the dominant variant), boosters from all three vaccine manufacturers were used induced good immune responses in about 450 people who received different vaccines. In the study, Moderna’s booster showed the most robust response. However, this study examined a full dose of Moderna and not the approved half dose of the company’s booster, which could minimize Moderna’s advantage over Pfizeras The Atlantic reported.

If you’re looking to move from Pfizer to Moderna or vice versa, the answer to a benefit may be a little less clear than the data or recommendations for Johnson & Johnson. But the Pfizer and Moderna vaccines are “not interchangeable,” said Dr. Eric Topol, Professor of Molecular Research at Scripps Research said on Twitter while suggesting that the differences between the vaccines might be of enough benefit for someone to consider switching.

If due to a medical condition or age, the best refresher may be the one most comfortable for you. People age 50 and older with a condition and adults age 65 and older are most likely to benefit from a second booster shot right now, CDC Director Dr. Rochelle Walensky said Wednesday.

If you have specific questions about which syringe is best for you, consult your doctor.


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

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Can I mix and match the first two shots?

No, health authorities’ permission to mix COVID-19 vaccines is for booster shots only. So far, the FDA has only approved one mixed-batch booster, meaning the first batch of coronavirus vaccines must consist of two doses of Moderna or Pfizer, or one dose of Johnson & Johnson.

Further data on mixing for booster shots will inform decisions about the co-use of primary coronavirus vaccine series, which could make it easier to reach underserved communities and potentially reduce health care and vaccine inequality.

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 healthcare provider with any questions about a medical condition or health goals.

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