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CDC reminder: COVID vaccine take 2 weeks to fully kick in after last dose

Staff Sgt. Ayanna McFaddin of the National Guard gives the Pfizer Biotech Covid-19 Vaccination on March 3 at the Holland Civic Center Place. A new CDC study underscores the effectiveness of the two-dose COVID vaccines once recipients are fully vaccinated.
Staff Sgt. Ayanna McFaddin of the National Guard gives the Pfizer Biotech Covid-19 Vaccination on March 3 at the Holland Civic Center Place. A new CDC study underscores the effectiveness of the two-dose COVID vaccines once recipients are fully vaccinated. (Bridge photo by Daytona Niles)

July 27: CDC recommends indoor mask use. But don’t expect mandates in Michigan

Not so fast.

If you’re still wearing a bandage from your second Pfizer or Moderna COVID vaccine, it’s probably too soon to strip off that mask with your friends, a new federal study indicates.

Based on data from 14 states including Michigan, the study confirms what doctors have been saying from the get-go: Immunity from the vaccine is excellent, but takes some time to fully build in your body. 

    In fact, there’s no protection at all immediately after the first of the two-shot vaccine regimen.


    It takes 14 days after a second shot of the two-dose vaccines to fully prime your immunity against COVID-19, a new report from the U.S. Centers for Disease Control and Prevention confirms.

    The two vaccine doses are usually given about three to four weeks apart. In the two weeks after the first dose, up through the first days after the second dose, the vaccines offer 64 percent protection against COVID-19, the study found. 

    “Protection grows over time,” said Emily Toth Martin, a University of Michigan epidemiologist and one of the report’s authors.

    Martin was one of several Michigan scientists who contributed data and input to the latest installment of the CDC’s Morbidity and Mortality Weekly Report — an important data source delivered to scientists each week. 

    The report underscores the level of patience required of vaccinated people as state and federal authorities are loosening guidelines for mask wearing and social interactions during the pandemic. The CDC released new guidelines Tuesday, saying fully vaccinated people can meet with each other in small groups with “minimal risk.”

    The key word, Toth said, is “fully” vaccinated, signaling that full immunity doesn’t build for up to 14 days after the second Moderna or Pfizer shot.

    “It’s an important message,” Toth told Bridge Michigan. “You've got to wait for it to start to work. You can't just get vaccinated, immediately go and start having high-risk behavior.”

    On Thursday, Gov. Gretchen Whitmer announced a “Vacc to Normal” plan that ties Michigan’s ability to loosen COVID restrictions to the pace at which state residents get vaccinated.  

    The CDC vaccine report focused on whether the two authorized mRNA vaccines, Moderna and Pfizer, were as effective in the real world as they were in clinical trials, where they had shown a 94-95 percent efficacy rate.

    Emily Toth Martin
    It takes time, not just a shot, to get fully immunized against COVID, said Emily Toth Martin, epidemiologist at the University of Michigan and a study author. (Bridge file photo)

    Researchers tracked ER visits and hospital admissions among people aged 65 and over in 14 states, including patients at U-M and parts of the Henry Ford Health System and St. Joseph Mercy Health System, over a nearly three-month period.

    The study reviewed only the most severe cases — those that prompted a trip to the hospital. Still, the results were “outstanding,” said Dr. Anu Malani, medical director of infection prevention and control at St. Joseph Mercy Health System, and another of the report’s authors.

    At the 24 hospitals, 398 of 417 patients, or more than 95 percent, weren’t vaccinated at all or were considered only partially vaccinated because they were sick before the end of the 14-day waiting period after a second dose.

    Just 19 patients — less than 5 percent — were considered fully vaccinated.

    Researchers didn’t consider the single-dose Johnson & Johnson vaccine because it wasn’t as widely used during the time period of the study.

    The study results confirmed the vaccine efficacy of 94-95 percent Pfizer and Moderna had announced during clinical trials last year, which were crucial in the vaccines’ authorization in December. The results also add to the growing evidence of the vaccines’ effectiveness in protecting people from COVID-19 or limiting the seriousness of their symptoms.

    Last fall, before the Pfizer and Moderna vaccines were approved for emergency use, Michigan residents over age 60 — considered the most vulnerable to the virus’ worst outcomes — made up 22.2 percent of Michigan’s COVID cases. 

    But after Michigan seniors were prioritized for getting early vaccines, the study showed, they comprised just 13.5 percent of new cases.

    Though the disease remains most lethal for seniors, their overall death rates have dropped as fewer of them contract COVID-19.

    Dr. Anu Malani
    “This is published evidence … that vaccines really are the way out of this,” said Dr. Anu Malani, a study author and infection prevention expert at St. Joseph Mercy Health System. (Courtesy photo)

    “[Clinical] trials are one thing. They are controlled … but I think the real world, what's happening, seeing people in the hospital — I think that's important,” St. Joseph’s Malani said of the report. “This is published evidence from multiple states, saying that vaccines really are the way out of this” pandemic. 

    Released Wednesday, the CDC study was limited to patients 65 and older, with the average age being 73. There’s reason to believe the results would be even more promising for younger vaccine recipients, Martin and Malani said.

    That’s because older residents often can’t muster the same immune response as their younger counterparts.

    “The take home (lesson) is that, with the vaccines, your risk of ending up in the hospital and having a really severe outcome is really really low,” Malani said.

    Bridge reporter Mike Wilkinson contributed to this report.

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