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Federal Register / Vol. 86, No. 116 / Monday, June 21, 2021 / Rules and Regulations requiring hospitalization and those resulting in death, as well as less severe symptomatic infections.
As stated above, the three authorized vaccine were shown to be highly efficacious in clinical trials. Clinical trial results are commonly considered a best case scenario e.g., conducted in relatively young and healthy populations, while evidence from follow-up observational studies provides insight on a more diverse population. This essential data from observational studies in populations who were vaccinated outside of clinical trials is emerging and shows that the mRNA vaccines are highly effective. At this time, observational studies for the single dose, viral vector vaccine are not available. Some of the studies for mRNA
vaccines examined high-risk populations, such as healthcare workers. Thus, the degree of protection in these studies can be extrapolated to a wide range of workplace settings in healthcare. The results from these studies are very encouraging.
A study of 3,950 health care personnel, first responders, and other essential workers who completed weekly SARSCoV2 testing for 13
consecutive weeks reported 90%
effectiveness 95% confidence interval CI = 68%97% after full vaccination with either mRNA vaccine Thompson et al., April 2, 2021. Still, 22.9% of PCR-confirmed infections required medical care; these included two hospitalizations but no deaths. A study of more than 8,000 individuals in the U.S. general population found that two doses of either mRNA vaccine were 88.7% effective in preventing SARS
CoV2 infection Pawlowski et al., February 27, 2021. Similar to the above results in essential workers, although breakthrough infection occurred, vaccinated patients in this study who were subsequently diagnosed with COVID19 had significantly lower 14day hospital admission rates than matched unvaccinated participants 3.7% vs. 9.2%. Hall et al., April 23, 2021, in a study of U.K. healthcare workers with bi-weekly testing, documented an 85% effectiveness of the Pfizer-BioNTech vaccine, though those authors required only one week after dose two for classification as fully vaccinated. Research from Israel provides additional evidence of high effectiveness for the Pfizer-BioNTech vaccine Dagan et al., February 24, 2021.
Data available regarding vaccine efficacy against some SARSCoV2
variants of concern illustrate that the vaccines remain effective at reducing symptomatic infections. Two doses of
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the Pfizer-BioNTech COVID19 vaccine was highly effective 8586% against SARSCoV2 infection and symptomatic COVID19 during a period when B.1.1.7 was the predominant circulating strain in the UK Hall et al., April 23, 2021. In Israel, the PfizerBioNTech vaccine was 92% effective even with the proportion of cases due to the B.1.1.7 becoming the dominant virus in circulation towards the end of the evaluation period Dagan et al., February 24, 2021. Another study testing the Pfizer-BioNTech COVID19
vaccine found that it was equally capable of neutralizing the notable variants from the United Kingdom and South Africa Xie et al., February 8, 2021. This finding was then reflected in a Qatari study that found that the PfizerBioNTech vaccine was not only effective at preventing disease in people infected by those variants, but was observed as 100% effective in preventing fatalities from COVID19
Abu-Raddad et al., May 5, 2021. The Janssen vaccine clinical trial was conducted during a time in which SARSCoV2 variants were circulating in South Africa B.1.351 variant and Brazil P.2 variant. At 28 or more days past vaccination, efficacy against moderate to severe/critical disease was 72% in the United States; 68% in Brazil;
64% in South Africa FDA, February 26, 2021. Although some studies have reported antibodies to be less effective against the B.1.351 variant, antibody activity in serum from vaccinated persons was generally higher than activity from serum of persons who recovered from COVID19 CDC, April 2, 2021.
A major question not fully addressed in the original clinical trials is whether vaccinated individuals can become infected and shed virus, even if they are asymptomatic. Thompson et al., April 2, 2021, reported that 11% of the PCRconfirmed breakthrough infections in their essential worker population were asymptomatic, indicating a concern for asymptomatic transmission. However, this concern is based on studies indicating asymptomatic transmission among unvaccinated individuals and it is not known if this phenomena occurs in infected vaccinated individuals. In the Moderna clinical trial, reverse transcription polymerase chain reaction RTPCR testing was performed on participants at their second vaccination visit; asymptomatic positives in the vaccinated group were less than half those in the placebo group Baden et al., December 30, 2020, supplemental files Table s18. In a Mayo clinic study, an 80% reduction in risk of positive pre-

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procedural screening tests was observed in patients tested after their second vaccine dose Tande et al., March 10, 2021. A study of more than 140,000
healthcare workers and their almost 200,000 household members reported a 30% reduction in risk of documented COVID19 cases in the household members after the healthcare provider was fully vaccinated Shah et al., March 21, 2021. In the Israeli general population, the estimated vaccine effectiveness for the asymptomatic infection proxy group infection without documented symptoms, which could have included undocumented mild symptoms was 90% at 7 or more days after the second dose Dagan et al., February 24, 2021. Preliminary data from Israel suggest that people vaccinated with the Pfizer-BioNTech COVID19 vaccine who develop COVID19 have a four-fold lower viral load than unvaccinated people LevineTiefenbrun, February 8, 2021. As noted by CDC April 2, 2021, this observation may indicate reduced transmissibility, because viral load is thought to be a major factor in transmission Marks et al., February 2, 2021.
The CDC has acknowledged that a growing body of evidence suggests that fully vaccinated people are less likely to have asymptomatic infection or transmit SARSCoV2 to others CDC, April 2, 2021. The decreased risk for infection, especially serious infection, combined with decreased risk of transmission to others has allowed the CDC to relax some recommendations for individuals who are in community or public settings and who are fully vaccinated with one of the three FDA authorized vaccines, as follows.
Quarantine is no longer required for fully vaccinated individuals who remain asymptomatic following exposure to a COVID19 infected person CDC, May 13, 2021.
Testing following a known exposure is no longer needed for a fully vaccinated person, as long as the individual remains asymptomatic and is not in specific settings such as healthcare CDC, April 27, 2021a, nonhealthcare congregate facilities e.g., correctional and detention facilities, homeless shelters or high-density workplaces e.g., poultry processing plants CDC, May 13, 2021.
In non-healthcare settings, fully vaccinated people no longer need to wear a mask or physically distance, except where required by federal, state, local, tribal, or territorial laws, rules, and regulations, including local business and workplace guidance CDC, May 13, 2021. In healthcare settings, the picture is more mixed. While the
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