COVID-19 Booster Vaccine: A Timeline for Third Dose Effectiveness and Immunity – GoodHousekeeping.com

With the confirmation of the brand new Omicron COVID-19 variant in the United States and with new cases of the disease projected to spread over the December holiday season Americans are queueing up for additional doses of their vaccines.

Officials at the World Health Organization classified Omicron, the latest variant of the SARS-CoV-2 virus that leads to a COVID-19 diagnosis, as a "variant of concern" just a few days after it was first reported by scientists; the announcement coincides with expanded eligibility for third dose and booster shots for all Americans who have received their first initial vaccines at least two months (for Johnson & Johnson recipients) or six months (Pfizer, Moderna) prior.

Because COVID-19 vaccines were just developed this year, messaging earlier in the pandemic was unclear on how long the immunity earned from a vaccine would last. Leading health officials at the Centers for Disease Control and Prevention have since clarified that booster vaccines (or additional doses for immunocompromised individuals) are necessary to replenish your body's protection against COVID-19 infection as immunity wanes over time; and since we're still in the thick of the global pandemic, expanding eligibility to all Americans for a booster dose ensures most will keep an optimal amount of antibodies during the winter season into the new year.

How long exactly does it take for a booster dose to impact our immune system? If you've already been vaccinated, especially with a two-dose mRNA vaccine series made in part by teams at Pfizer or Moderna, you may recall hearing that you weren't "fully" vaccinated until two weeks out from your last shot.

The logic and subsequent timeline may not be exactly the same for those who are receiving additional doses this month, which is good news for those who are seeking protection against viral variants, including Omicron.

Data suggests that the immune response to an additional COVID-19 vaccine dose is different than when your body is first introduced to the vaccine and experts are breaking down what that means for you below.

Put simply: It all depends on whether this is your initial COVID-19 vaccine, or if you've already received a full vaccination series prior (or at least one dose of the Johnson & Johnson vaccine). During your first vaccine, your body's immune system becomes active and builds antibodies to SARS-CoV-2 within two weeks of your first shot. Federal guidance indicates that people are "fully" vaccinated with mRNA immunity about 2 weeks after your second dose and two weeks after the single Johnson & Johnson shot.

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But as we know, high immunity can't last forever, and scientists have spent the bulk of this year determining how effective COVID-19 vaccines are in real-time. "Detectable antibodies peak around two to three months after full immunization, and then begin to wane thereafter," explains Shruti Gohil, M.D., University of California Irvine Health's associate director of epidemiology and infection prevention as well a professor at the UCI School of Medicine

Dr. Gohil cites current research that suggests the majority of people experience waning levels of COVID-19 antibodies around 6 months after vaccination. It's not that one won't have any protection against COVID-19 at this point, she stresses, but "having fewer circulating antibodies means there will be a delay in your immune response to COVID infection compared to when antibodies are circulating in greater numbers."

Additional doses of the vaccine, then, will "revive your circulating antibody population sufficient to reduce your risk of infection," Dr. Gohil adds.

There isn't as much established research or federal health guidance in understanding when immunity has reached its peak after a booster COVID-19 vaccine, but experts are aware that the process likely occurs faster for most based on their knowledge of how vaccines work in the first place. After all, your immune system has been previously introduced to the vaccine by the time you receive a booster shot.

A pre-print study of research conducted in Israel, which has yet to be peer-reviewed, indicated that immunity may be heightened within just one week of a booster shot. And the effectiveness of the booster is likely doubled in the second week. "We found that seven to 13 days after the booster shot, there is a 4868% reduction in the odds of testing positive for SARS-CoV-2 infection," the Maccabi Healthcare Services researchers shared.

Dr. Gohil indicates that most healthcare providers in the U.S. have been sharing similar figures with their patients.

"Boosting should result in antibody production within days of the booster vaccine, but peak levels still occur around the two-week mark, similar to initial vaccines," she tells Good Housekeeping. "Why? The speed of the antibody production is determined by the same mechanisms the cells are using the same 'machinery' with the same turnaround time as they did the first time around."

Ultimately, you should rest easy knowing that your body's immune response kicks in almost immediately after a booster dose. But expect to enjoy a higher level of protection around two weeks after your latest dose.

Anyone over the age of 18 is now eligible for a booster COVID-19 vaccine, as long as it's been two months for Johnson & Johnson recipients or six months for those who signed up for any two-dose mRNA vaccine. So far, according to official CDC data, around 15% of those who are now eligible for this vaccine have received a booster.

Federal health officials have also approved mixing and matching of various manufactured COVID-19 vaccines. Most healthcare professionals recommend sticking with the same type of shot you received on your first vaccination, unless you received a Johnson & Johnson single-dose shot. You should consult your primary healthcare provider if you have questions about which vaccine you should receive as a booster, as some research has indicated that Moderna boosters may provide some form of enhanced protection, as reported by the Los Angeles Times.

But if you only have access to one kind of shot Pfizer or Moderna alone you shouldn't delay a booster altogether, as they're necessary to keep safe during the coming weeks and months, when transmission risk is expected to skyrocket.

When it comes to earlier strains of COVID-19, including Beta, Lambda, even Delta, federal health officials say a booster vaccine can help keep you as protected as possible from becoming sick this winter. It's especially crucial as flu season is also predicted to impact many Americans, and immune systems can easily be overwhelmed with two infections at once.

As far as Omicron goes, researchers still have a lot to learn about this version of the virus. Dr. Gohil adds that it's too early to say whether current vaccines can provide perfect protection against this variant, but that everyone in the scientific medical community believes that additional antibodies always equate to better protection overall.

"Although Omicron is very different from the original variant to which the vaccines were made, and we expect efficacy to be lower for this variant, we would still expect some amount of cross-reactive antibodies that could potentially afford protection," she explains.

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COVID-19 Booster Vaccine: A Timeline for Third Dose Effectiveness and Immunity - GoodHousekeeping.com