New CDC data shows Covid-19 vaccines developed by Pfizer/BioNTech and Moderna are highly effective in real-world conditions. But even as the vaccines continue to roll out, coronavirus cases are rising again, leading President Biden to urge states to reimpose or sustain coronavirus-related restrictions.

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CDC data confirms the effectiveness of mRNA Covid-19 vaccines

CDC on Monday released a Morbidity and Mortality Weekly Report focused on Covid-19 vaccines developed by Pfizer/BioNTech and Moderna using messenger RNA (mRNA). Each of the vaccines require that patients receive two doses a few weeks apart.

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For the study, CDC researchers evaluated the effectiveness of mRNA Covid-19 vaccines by examining coronavirus cases among 3,950 health care workers, first responders, and other essential workers in six states over a 13-week period from Dec. 14, 2020, to March 13, 2021. Each participant self-collected a nasal swab each week, and the samples were sent to Marshfield Clinic Research Institute, the research division of Marshfield Clinic Health System, for testing to identify symptomatic and asymptomatic coronavirus cases.

Among the participants with no previous confirmed coronavirus cases, 477—or 12.1%—received only one vaccine dose during the period examined, while 2,479—or 62.8%—received two vaccine doses.

Overall, the researchers found the vaccines were 80% effective at preventing infections two weeks after participants received their first vaccine dose and 90% effective two weeks after participants received their second vaccine dose. According to STAT News, CDC's findings are consistent with the efficacy rates reported by Pfizer/BioNTech and Moderna in clinical trials.

The researchers identified 58% of coronavirus cases among participants through weekly testing before the participants developed symptoms, and they confirmed 42% of cases after participants developed symptoms and underwent testing. Most of the participants who tested positive for the coronavirus developed Covid-19 symptoms, but 10.7% had no symptoms. Among those who tested positive for the coronavirus, 23% required medical care, and two were hospitalized. No deaths occurred in the study.

"This study shows that our national vaccination efforts are working," CDC Director Rochelle Walensky said. "The authorized vaccines are the key tool that will help bring an end to this devastating pandemic."

'This is not a time to lessen our efforts'

The new findings come as President Biden and top health officials on Monday urged Americans to remain vigilant and continue to follow precautions aimed at preventing the coronavirus's spread as recent data indicates the number of coronavirus cases is climbing once again.

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"This is not a time to lessen our efforts," Biden said. "If we let our guard down now, we could see the virus getting worse, not better." Biden called on state officials to pause their plans to reopen and reimplement mask mandates.

"Reinstate the mandate if you let it down, and businesses should require masks as well," Biden said. "A failure to take this virus seriously—precisely what got us into this mess in the first place—risks more cases and more deaths."

Similarly, Walensky urged all Americans, including elected officials and community leaders, to get vaccinated and continue to practice social distancing and wearing face masks to contain the coronavirus's spread. Walensky said, "I am asking you to just hold on a little longer, to get vaccinated when you can, so that all of those people that we all love will still be here when this pandemic ends."

Walensky added, "I'm going to reflect on the recurring feeling I have of impending doom. We have so much to look forward to, so much promise and potential of where we are and so much reason for hope. But right now, I'm scared."

Experts have said the recent uptick in coronavirus cases likely stems from two key factors: states easing coronavirus-related restrictions, and the spread of more transmissible coronavirus variants.

According to data compiled by the Times, the United States' average daily number of newly reported coronavirus cases over the past week was 65,382—up by 19% compared with the average from two weeks ago.

The Times' data showed that, as of Tuesday morning, the rates of newly reported coronavirus cases were "staying high" in the U.S. Virgin Islands and 25 states that have reported a daily average of at least 15 newly reported cases per 100,000 people over the past week. Those states are Colorado, Connecticut, Delaware, Florida, Idaho, Illinois, Iowa, Maryland, Massachusetts, Michigan, Minnesota, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Vermont, Virginia, and West Virginia.

In addition, the rate of newly reported coronavirus cases was "going up" as of Tuesday morning in Hawaii, Indiana, Missouri, Puerto Rico, and Washington, which have had comparatively lower case rates, the Times reports.

Even as cases are increasing, new hospitalizations and deaths are continuing to decline. According to the Times' data, 39,924 Americans with Covid-19 were hospitalized on Monday—down by 5% from the average from two weeks ago. Further, 685 new deaths were linked to the coronavirus on Monday, down 29% from the average two weeks ago.

(Kolata, New York Times, 3/29; Hopkins, Wall Street Journal, 3/29; Branswell, STAT News, 3/29; Banerjee/Chander, Reuters, 3/29; Miller, Associated Press, 3/30; Bernstein et al., Washington Post, 3/29; Owermohle/Banco, Politico, 3/29; LaFraniere/Stolberg, New York Times, 3/29; New York Times, 3/29).