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Federal Register / Vol. 86, No. 116 / Monday, June 21, 2021 / Rules and Regulations
lead to one additional case. As long as a virus has an R0 of more than 1, it is expected to continue to spread throughout the population. The observed R0 also known as simply R
must be below 1 to prevent sustained spread; such a reduction can be achieved through infection control interventions e.g., vaccination, nonpharmaceutical interventions that either reduce the susceptibility of the population to the virus or reduce the likelihood of transmission within the population Delamater et al., 2019.
During the early part of the COVID19
outbreak in China, before consistent protective measures were put into place, the R0 for SARSCoV2 was estimated as 2.2 Riou and Althaus, January 30, 2020. Higher estimates of the R0 early in China 5.7 have also been published Sanche et al., April 7, 2020. R0 ranges from 2 to 5 have been published for earlier MERS and SARSCoV1
coronavirus outbreaks WHO, May 2003;
Choi et al., September 25, 2017. Since the start of the COVID19 pandemic, the R0 has varied depending on the natural ebb and flow of rolling infection surges as well as the fluctuating nonpharmaceutical interventions NPIs put in place, such as face coverings, nonessential business shutdowns, and testing with follow-up isolation and quarantining. The R0 value in the U.S.
early in the pandemic was estimated to be approximately 2 Li et al., October 22, 2020, and this value has generally remained above 1 for the country as a whole throughout the pandemic, with various states well above and below this value at various times Harvard Chan School of Public Health, February 26, 2021; Shi et al., May 18, 2021.
Pre-symptomatic and asymptomatic transmission are significant drivers of the continued spread of COVID19
Johansson et al., January 7, 2021.
Individuals are considered most infectious in the 48 hours before experiencing symptoms and during the first few symptomatic days Cevik et al., October 23, 2020. The time it takes for a person to be infected and then transmit the virus to another individual is called the serial interval. Several studies have indicated that the serial interval for COVID19 is shorter than the time for symptoms to develop, meaning that many individuals can transmit SARSCoV2 before they begin to feel ill Nishiura et al., March 4, 2020;
Tindale et al., June 22, 2020. It is also possible for individuals to be infected and subsequently transmit the virus without ever exhibiting symptoms. This is called asymptomatic transmission. As noted earlier, a recent meta-analysis
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reviewed 13 studies in which the asymptomatic prevalence ranged from 4% to up to 41% Byambasuren et al., December 11, 2020.
The existence of both presymptomatic transmission and asymptomatic infection and transmission pose serious challenges to containing the spread of the virus.
Although the risk of asymptomatic transmission is 42% lower than from symptomatic COVID19 patients Byambasuren et al., December 11, 2020, asymptomatic transmission may result in more transmissions than symptomatic cases, perhaps because asymptomatic persons are less likely to be aware of their infection and can unknowingly continue to spread the disease to others. Similarly, presymptomatic individuals can transmit the virus to others before they know they are sick and should isolate, assuming they are aware of their exposure. Existing evidence demonstrates that asymptomatic transmission is a significant contributor to the spread of COVID19 in the United States. Johansson et al., January 7, 2021 conducted a study to assess the proportion of SARSCoV2
transmission from pre-symptomatic, never symptomatic, and symptomatic individuals in the community. Based on their modeling, they found 59% of transmission came from asymptomatic transmission, including 35% from presymptomatic individuals and 24% from individuals who never develop symptoms Johansson et al., January 7, 2021.
The SARSCoV2 virus also regularly mutates over time into different genetic variants. Many of these variants results in no increase in transmission or disease severity. However, the CDC monitors for variants of interest, variants of concern, and variants of high consequence CDC, May 5, 2021. A variant of interest is one with specific genetic markers that have been associated with changes to receptor binding, reduced neutralization by antibodies generated against previous infection or vaccination, reduced efficacy of treatments, potential diagnostic impact, or predicted increase in transmissibility or disease severity CDC, May 5, 2021. CDC-listed variants of interest include strains first identified in the United States e.g., B.1.526, B.1.526.1, the United Kingdom e.g., B.1.525, and Brazil e.g., P.2. A variant of concern is one for which there is evidence of an increase in transmissibility, more severe disease e.g., increased hospitalizations or deaths, significant reduction in neutralization by antibodies generated during previous infection or
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vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures CDC, May 5, 2021.
CDC-listed variants of concern include strains first identified in the United States e.g., B.1.427, B.1.429, United Kingdom e.g., B.1.17, Brazil e.g., P.1, and South Africa e.g., B.1.351. As of April 24, B.1.1.7 made up 60% of infections in the United States CDC, May 11, 2021. CDC notes that B.1.1.7 is associated with a 50% increase in transmission, as well as potentially increased incidence of hospitalizations and fatalities CDC, May 5, 2021. As new strains with increased transmissibility or more severe effects enter the U.S. population, healthcare workers may be among the first to be exposed to them when those who are infected seek medical care Howard, May 22, 2021.
OSHA also recognizes that reported cases of SARSCoV2 likely undercount actual infections in the U.S. population.
This finding is based on seroprevalence data, which measure the presence of specific antibodies in the blood that are typically developed when an individual is infected with SARSCoV2. Reported cases, in contrast, are based on COVID
19 tests that measure active infections.
Recent reported case numbers suggest that approximately 10% of the US
population has been infected. However, only seven states reported seroprevalence below 10% i.e., Alaska, Hawaii, Maine, New Hampshire, Oregon, Vermont, Washington and 23
states plus Washington DC and Puerto Rico exceeded 20% CDC, May 14, 2021. The likely reason for this difference is that serological tests measure antibodies in the blood that can be detected for a longer period of time than can an active COVID19 infection.
As such, serological testing may be able to detect past COVID19 infections in individuals who never sought out a viral test. A sampling of states from the Nationwide Commercial Laboratory Seroprevalence Survey illustrates this CDC, May 14, 2021. On March 30, 2021, California had reported 3,564,431
cases, but seroprevalence estimates indicate that there have been 7,986,000
cases in the state 95% CI: 7,023,000
8,965,000. Similarly, Texas has reported 2,780,903 cases, but seroprevalence data indicate 6,692,000
cases 95% CI: 5,624,0007,819,000.
Given the very real possibility of higher numbers of cases than are reported in national case counts, the disease burden discussed in this document may well be underestimated.

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