Coronavirus not under control in US, relaxing social distancing could double the deaths in two months: Study
Increasing surveillance and monitoring capacities will be essential to avoid a second wave, warn scientists
In the US, May 25 is Memorial Day, which marks the unofficial start of the American summer. Every state is relaxing quarantine rules to some extent, betting that the country finally has Covid-19 under control. The coronavirus pandemic, however, is not under control in much of the US and increased mobility as lockdown measures are eased could result in a surge of coronavirus infections and deaths, warn scientists.
An estimated 24 states still have a reproduction number above the critical threshold of one, meaning that each coronavirus patient is infecting more than one person, according to the research team from Imperial College London. Texas tops the list, followed by Arizona, Illinois, Colorado, Ohio, Minnesota, Indiana, Iowa, Alabama, Wisconsin, Mississippi, Tennessee, Florida, Virginia, New Mexico, Missouri, Delaware, South Carolina, Massachusetts, North Carolina, California, Pennsylvania, Louisiana and Maryland. Any reproduction rate above one means the virus spreads exponentially. According to the experts, for an outbreak to be under control, the reproduction has to be below one, but only 15.7% of states "have 95% credible intervals that are completely below one".
The scientists also found that increased mobility following the relaxation of social distancing rules could lead to the doubling of Covid-19 deaths over the next two months.
The team calculated how many people in each US state have been infected with Covid-19 and how many people are currently infectious. Their estimates rely on death data, which they say is the most reliable and consistent source of information on the spread of the pandemic. The researchers also incorporate patterns of human movement in their epidemiological model. "We model the epidemics in the US at the state-level, using publicly available death data. For each state, we estimate the time-varying reproduction number (the average number of secondary infections caused by an infected person), the number of individuals that have been infected, and the number of individuals that are currently infectious. We use changes in mobility as a proxy for the impact that non-pharmaceutical interventions (NPIs) and other behavior changes have on the rate of transmission of SARS-CoV-2 (the virus that causes Covid-19)," the research team says in their findings.
Nationally, the estimates show that the percentage of individuals that have been infected is 4.1% (ranging between 3.7%-4.5%), with wide variation between states. For all states, even for the worst affected states, the team estimates that less than a quarter of the population has been infected. In New York, for example, analysis shows that 16.6% (12.8%-21.6%) of individuals have been infected to date. New Jersey has an attack rate of 16.1%, while Connecticut, Massachusetts and Washington, DC all have attack rates of over 10%.
Earlier in the outbreak, the US had an initial 2.2 national average reproduction number. The findings reveal that while all US states have substantially reduced their reproduction numbers, there is no evidence that any state is approaching herd immunity or that its epidemic is close to over. The team says that without changes in behavior that result in reduced transmission, or interventions such as increased testing that limit transmission, new infections of COVID-19 are likely to persist and in the majority of states, grow.
The findings bolster the warnings being made by many scientists in the US about the loosening of restrictions. Accordingly, as states reopen, the Imperial modelers recommend careful surveillance and monitoring to avoid a deadly second wave. "Our estimates suggest that the epidemic is not under control in much of the US. As of May 17, 2020, the reproduction number is above the critical threshold (1.0) in 24 states. Higher numbers are geographically clustered in the South and Midwest, where epidemics are still developing, while we estimate lower reproduction numbers in states that have already suffered high Covid-19 mortality (such as the Northeast). These estimates suggest that caution must be taken in loosening current restrictions if effective additional measures are not put in place," the researchers caution.
The report examines the impact of relaxing social distancing measures with a 20% and 40% return in mobility. The report does not address the potential effect of additional behavioral changes or interventions such as increased mask-wearing or testing and tracing strategies. In addition, it assumes the relationship between mobility and transmission remains unchanged. The estimates illustrate the potential consequences of increasing mobility across the general population: in almost all cases, after eight weeks, a 40% return to baseline leads to an epidemic larger than the current wave.
"We predict that deaths over the next two-month period could exceed current cumulative deaths by greater than two-fold if the relationship between mobility and transmission remains unchanged. Our results suggest that factors modulating transmission such as rapid testing, contact tracing, and behavioral precautions are crucial to offset the rise of transmission associated with loosening of social distancing," says the research team.
As of May 24, over 1,622,610 coronavirus cases have been reported across the US and more than 97,080 have died in the Covid-19 pandemic, according to data compiled by Johns Hopkins.