Zie ook in gerelateerde artikel. 

1 april 2021: Bron: CDC, Centers for Diasease Control and Prevention

Een vaccinatie tegen het coronavirus - Covid-19 beschermt zowel de persoon die zich laat vaccineren zelf als zorgt ervoor dat deze persoon ook anderen niet besmet. Dat blijkt uit een nieuwe studie gepubliceerd door het CDC - Centers for Diasease Control and Prevention.
Na de eerste prik daalde de besmettingskans binnen twee weken met 80 procent, na de tweede prik zelfs met 94 procent liet een studie zien bij 3.950 gezondheidswerkers, hulpverleners en anderen werknemers die door hun werk een hoge kans liepen om besmet te worden met het Coronavirus - Covid-19. De onderzoekers namen in drie maanden (tussen 14 december 2020 en 13 maart 2021) elke week een PCR-test af bij de mensen, of ze nu wel of geen klachten hadden. 

De Amerikaanse studie onderzocht de effecten van de mRNA-vaccins, zoals die van Pfizer/BioNTech en Moderna. Maar de onderzoekers verwachten dat dit ook geldt voor andere vaccins.

Hier de originele studie, abstract staat onderaan artikel. 

Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

In Nature werd een Israelische studie gepubliceerd die nagenoeg dezelfde resultaten laat zien over de effectiviteit van het Pfizer/BioNTech-vaccin met ook een 90 procent bescherming. Ouderen boven de 80 jaar en mensen met onderliggende medische aandoeningen als diabetes of COPD reageerden wel duidelijk minder op het vaccin.

Zie dit studieverslag. 

Initial report of decreased SARS-CoV-2 viral load after inoculation with the BNT162b2 vaccine

Dit is het persbericht dat het CDC liet uitgaan nav hun laatste studie :

CDC Real-World Study Confirms Protective Benefits of mRNA COVID-19 Vaccines

Study involved health care personnel, first responders, and essential workers in six states

Press Release

Embargoed until: 11 a.m. ET, Monday, March 29, 2021
Contact: Media Relations
(404) 639-3286

A new CDC study provides strong evidence that mRNA COVID-19 vaccines are highly effective in preventing SARS-CoV-2 infections in real-world conditions among health care personnel, first responders, and other essential workers.  These groups are more likely than the general population to be exposed to the virus because of their occupations.

The study looked at the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines in preventing SARS-CoV-2 infections among 3,950 study participants in six states over a 13-week period from December 14, 2020 to March 13, 2021.

Results showed that following the second dose of vaccine (the recommended number of doses), risk of infection was reduced by 90 percent two or more weeks after vaccination. Following a single dose of either vaccine, the participants’ risk of infection with SARS-CoV-2 was reduced by 80 percent two or more weeks after vaccination.

It takes about two weeks following each dose of vaccine for the body to produce antibodies that protect against infection. As a result, people are considered “partially vaccinated” two weeks after their first dose of mRNA vaccine and “fully vaccinated” two weeks after their second dose. These new vaccine effectiveness findings are consistent with those from Phase 3 clinical trials conducted with the vaccines before they received Emergency Use Authorizations from the Food and Drug Administration. Those clinical trials evaluated vaccine efficacy against COVID-19 disease, while this study evaluated vaccine effectiveness against infection, including infections that did not result in symptoms.

“This study shows that our national vaccination efforts are working. The authorized mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation’s health care personnel, first responders, and other frontline essential workers,” said CDC Director Rochelle P. Walensky, MD, MPH. “These findings should offer hope to the millions of Americans receiving COVID-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead. The authorized vaccines are the key tool that will help bring an end to this devastating pandemic.”

One of this study’s strengths is its design: participants self-collected nasal swabs each week for RT-PCR laboratory testing, regardless of whether they had developed symptoms of illness.  Researchers were able to look for evidence of SARS-CoV-2 infection irrespective of symptoms. A small number (10.7 percent) of infections in this study were asymptomatic (i.e., did not result in symptoms). However, the majority of infections (58 percent) occurred among people whose infections were identified by testing before they developed symptoms or knew they were infected. The study demonstrates that these two mRNA vaccines can reduce the risk of all SARS-CoV-2 infections, not just symptomatic infections.

This is important because preventing both asymptomatic and pre-symptomatic infections among health care workers and other essential workers through vaccination can help prevent the spread of SARS-CoV-2 to those they care for or serve. Findings from this study complement earlier reports that these two mRNA COVID-19 vaccines can reduce both asymptomatic and symptomatic SARS-CoV-2 infections.

This study also provided positive news about partial (one-dose) vaccination. The one-dose VE estimate of this study (80 percent) is consistent with other recent VE studies following the first dose of Pfizer-BioNTech vaccine among health care providers.  Studies conducted in the United Kingdom and Israel showed that one dose was about 70 percent and 60 percent effective, respectively, against SARS-CoV-2 infection.  The current results provide reassurance that people start to develop protection from the vaccine two weeks after their first dose. The greatest protection was seen among those who had received both recommended doses of the vaccine.

This CDC study was conducted through the HEROES-RECOVER network, a network of prospective cohorts that share a common protocol and methods. This network is part of a vaccine effectiveness surveillance system made possible by federal pandemic flu preparedness funding.

This study is the first of many planned COVID-19 vaccine effectiveness studies CDC is conducting to evaluate the benefits of COVID-19 vaccines in various populations and across different outcomes, such as preventing infections, doctor’s visits, hospitalizations, or deaths. Results from these studies assist the medical and public health experts on the Advisory Committee on Immunization Practices and CDC to make important vaccine policy decisions aimed at saving lives.

The mRNA-1273 vaccine showed 94.1% efficacy at preventing Covid-19 illness, including severe disease.

Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

List of authors.
  • Lindsey R. Baden, M.D., 
  • Hana M. El Sahly, M.D., 
  • Brandon Essink, M.D., 
  • Karen Kotloff, M.D., 
  • Sharon Frey, M.D., 
  • Rick Novak, M.D., 
  • David Diemert, M.D., 
  • Stephen A. Spector, M.D., 
  • Nadine Rouphael, M.D., 
  • C. Buddy Creech, M.D., 
  • John McGettigan, M.D., 
  • Shishir Khetan, M.D., 
  •  for the COVE Study Group*



Vaccines are needed to prevent coronavirus disease 2019 (Covid-19) and to protect persons who are at high risk for complications. The mRNA-1273 vaccine is a lipid nanoparticle–encapsulated mRNA-based vaccine that encodes the prefusion stabilized full-length spike protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes Covid-19.


This phase 3 randomized, observer-blinded, placebo-controlled trial was conducted at 99 centers across the United States. Persons at high risk for SARS-CoV-2 infection or its complications were randomly assigned in a 1:1 ratio to receive two intramuscular injections of mRNA-1273 (100 μg) or placebo 28 days apart. The primary end point was prevention of Covid-19 illness with onset at least 14 days after the second injection in participants who had not previously been infected with SARS-CoV-2.


The trial enrolled 30,420 volunteers who were randomly assigned in a 1:1 ratio to receive either vaccine or placebo (15,210 participants in each group). More than 96% of participants received both injections, and 2.2% had evidence (serologic, virologic, or both) of SARS-CoV-2 infection at baseline. Symptomatic Covid-19 illness was confirmed in 185 participants in the placebo group (56.5 per 1000 person-years; 95% confidence interval , 48.7 to 65.3) and in 11 participants in the mRNA-1273 group (3.3 per 1000 person-years; 95% CI, 1.7 to 6.0); vaccine efficacy was 94.1% (95% CI, 89.3 to 96.8%; P<0.001). Efficacy was similar across key secondary analyses, including assessment 14 days after the first dose, analyses that included participants who had evidence of SARS-CoV-2 infection at baseline, and analyses in participants 65 years of age or older. Severe Covid-19 occurred in 30 participants, with one fatality; all 30 were in the placebo group. Moderate, transient reactogenicity after vaccination occurred more frequently in the mRNA-1273 group. Serious adverse events were rare, and the incidence was similar in the two groups.


The mRNA-1273 vaccine showed 94.1% efficacy at preventing Covid-19 illness, including severe disease. Aside from transient local and systemic reactions, no safety concerns were identified. (Funded by the Biomedical Advanced Research and Development Authority and the National Institute of Allergy and Infectious Diseases; COVE ClinicalTrials.gov number, NCT04470427. opens in new tab.)

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