The team from China, the United States, and Australia conducted a model study that found that only a vaccine that was nearly 100% effective would suppress the epidemic enough to bring the U.S. population back to pre-pandemic life and lose the need for social distancing and face masks.
If a high potency vaccine could not be obtained, using a moderately (80%) potency vaccine combined with 30 to 40% use of the face mask could be a plausible alternative, say the researchers.
“Vaccinations combined with a modest number of non-pharmaceutical measures such as the use of face masks in public spaces (shopping malls and transportation) could be a viable option to further suppress the epidemic in the long term,” writes Lei Zhang of Xi’a Jiaotong University Health Science center and colleagues.
The researchers say the study results could serve as a guide for plans to introduce vaccines and ongoing implementation of non-pharmaceutical interventions (NPIs).
A pre-print version of the paper is available on the server medRxiv *while the article is being peer reviewed.
Model calibration and data fitting based on reported confirmed COVID-19 cases and deaths in four states i.e. New York (ab), Texas (cd), Florida (ef) and California (gh). The blue areas indicate 95% confidence intervals. Dashed lines, dot-dash lines, and dotted lines denote the social distancing order (person-to-person contact rates have decreased), face mask order, and reopening (person-to-person contact rates have been restored from no more than 100% of the prepandemic level) Directives implemented in each state.
The United States was one of the hardest hit countries
Since the first cases of COVID-19 were first identified late last year (2019) in Wuhan, China, the unprecedented spread of the pandemic has had a devastating impact on global public health and the economy.
The impact in the United States has been particularly severe, with confirmed infections now exceeding 9.4 million and deaths exceeding 232,000.
Contour plots of infections averted as a function of vaccine effectiveness and vaccine coverage rate in four states, when social distancing is returned to pre-pandemic levels shortly after vaccination began. The first row preserves the use of face masks at baseline levels, the second row reduces the use of face masks to half the baseline level, and the third row does not use a face mask. The black solid isoclines indicate the threshold that the number of infections averted is zero. The black dashed lines represent the minimum vaccine effectiveness and vaccine coverage rate when the number of infections averted is zero.
With a number of vaccine candidates now entering Phase III clinical trials, there is growing hope that the restrictions on social distancing and the need to use face masks could soon be eased so that Americans can live like this again, as you know it.
However, the extent to which these control measures could be relaxed will depend on the effectiveness of the potential vaccines, which is currently unknown.
“In order to allow careful planning of what restrictions may need to continue, there is an urgent need for research to predict how the effectiveness of a potential vaccine may affect the course of the COVID-19 pandemic in the US,” they say Researcher.
It is also important to determine how the current NPIs could be incorporated into an overall control strategy that takes into account the different efficacy of different vaccines.
What did the researchers do?
The team developed dynamic simulation models for COVID-19 transmission for the four hardest-hit US states of New York, Texas, Florida and California.
The models are designed to account for the differences in social distancing and face mask guidelines that apply across states.
Researchers used the models to assess the level of vaccine effectiveness and coverage that would be needed to avert COVID-19 cases and deaths in scenarios where social contact returns to pre-pandemic levels and the use of Face masks should be reduced.
Each of the country-level models have been calibrated based on the latest daily and cumulative COVID-19 data (as of January 26)th until September 15thth, 2020) from the Coronavirus Resource Center at Johns Hopkins University.
What did the models predict?
Without a vaccine, the spread of COVID-19 across the four states could be suppressed by maintaining current social distancing measures and the use of face masks.
However, returning social contact to pre-pandemic levels without changing current face mask use requirements would lead to new outbreaks, Zhang and colleagues say.
That would result in 0.8 to 4 million infections and 15,000 to 240,000 deaths in the four states within a year.
In this scenario, introducing vaccination would help reduce the number of infections and deaths, even if the vaccine’s effectiveness and coverage were relatively poor, the researchers say.
However, if the rate of face mask use decreased by 50%, the introduction of a weak vaccine (only 50% effective) with little coverage would not be enough to suppress the epidemic.
If face mask use was halved in these states, a weak vaccine would require 55 to 94% population coverage to suppress the epidemic, while a moderately effective vaccine (80%) would require 32 to 57% coverage and a strong vaccine ( 100% effective) would only require 24 to 46% coverage.
However, if the use of face masks were stopped altogether, a weak vaccine would not be enough to suppress the epidemic, even with high coverage, and more major outbreaks would occur.
A moderate vaccine, on the other hand, would suppress the epidemic with coverage of 48 to 78%, while a strong vaccine would suppress it with coverage of 33 to 58%.
What do the researchers advise?
“Given that the willingness to take a COVID-19 vaccine in the US has been estimated at only 58%, just a strong vaccine with a high potency of nearly 100% would be enough to quell and ease the epidemic alone social distancing and face mask requirements, ”write Zhang and colleagues.
However, if a strong vaccine is not achievable, a moderately effective vaccine and face mask usage rate of around 30-40% would be a plausible alternative to achieve this goal.
“The results of this study provide up-to-date information that enables policymakers to plan the potential release of a COVID-19 vaccine and understand its effects in different regions of the US under different social distancing and face mask use scenarios,” the team concludes .
* Important NOTE
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.
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