Inadequate vaccine and epidemic control in the US

A new paper published on the preprint server medRxiv* in May 2020 shows that vaccination must be combined with nonpharmacological interventions (NPIs) to achieve rapid and effective control of the ongoing pandemic.

The appearance of the novel coronavirus infection COVID-19 in the USA poses a huge public health burden as well as severe economic hardship. The decline in productivity and health has already led to an unemployment rate causing a decrease in both human and economic productivity (translating to about 30% unemployment and a predicted decrease in GDP by 50% within a few months).

As of now, the lack of a vaccine or effective drugs against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to the use of NPIs, including physical distancing, regular and effective handwashing, wearing face masks outside the home and contact tracing, in addition to self-isolation and the quarantine of suspected COVID-19 cases.

NEW YORK - APRIL 01, 2020: An EMS worker outside of a Mount Sinai ambulance in Tribeca, New York City during the COVID-19 pandemic. Image Credit: Jennifer M. Mason / Shutterstock
NEW YORK - APRIL 01, 2020: An EMS worker outside of a Mount Sinai ambulance in Tribeca, New York City during the COVID-19 pandemic. Image Credit: Jennifer M. Mason / Shutterstock

The Vaccine Race

Multiple pharmaceutical companies and researchers are frantically working on a safe and inexpensive vaccine, which usually takes a decade or more. However, some researchers are trying to speed up vaccine studies and trials, such as fast-tracking the vaccine development against the virus.

Many agencies have already begun trials at some phase, to prove the efficacy of the vaccine molecule. The candidate vaccine developed by the Jenner Institute at Oxford University is currently in early trials. If all goes well, they hope the first few million doses will be on the market by September 2020.

Others have not been slow to follow. The current study by researchers at Arizona State University and University of Florida aims at filling the gap for the development and use of a mathematical model to evaluate what effect a vaccine would have on the disease.

The Effect of Social Distancing

The researchers simulated the first situation without either vaccination or public mask use. This is used to measure the impact of physical distancing measures when the latter is the only intervention used at the community level. This shows a significant reduction in the number of new cases from a projected 120,000 to about 64,000 with social distancing.

Vaccines are also not suitable for some groups:

  • Too young or with weak immunity
  • Too old, or another medical condition, or unwilling for traditional or religious reasons.

The Vaccination Percentage for Herd Immunity

The researchers then ask for the least percentage of the population that must be vaccinated to protect themselves and others from severe or critical diseases. This also includes those of advanced age or who opt out for cultural, traditional, or religious reasons.

The result will hopefully be herd immunity – when enough members of a community are infected and recover, the viral transmission is blocked so that non-immune individuals are also protected against the disease. The best way to achieve herd immunity is vaccination.

The researchers found that, according to their analysis, effective pandemic control in the U.S. is possible if vaccination over 90% is achieved. This refers to the use of a suboptimal vaccine with a protection rate of 80%. The use of masks as well by just half of Americans markedly reduces the percentage required to be vaccinated to 78%.

Combination of Vaccination with NPIs

The increase in vaccination rates from baseline will be small (about 10%) in states like Florida or New York but quite large in the USA as a whole. Nationwide prospects of viral elimination using the hypothetical imperfect vaccine are small due to the very high coverage required.

However, the study shows that “COVID-19 elimination (measured in terms of bringing Rc (the control reproduction number) to a value less than unity) is feasible even if social-distancing is implemented at a low level of effectiveness.”

With low and moderate effectiveness of social distancing, vaccination of at least 80% and 67% respectively will lead to the elimination of the virus in the U.S. According to the simulations, say the researchers, elimination of COVID-19 “using a vaccine is greatly enhanced if the vaccination program is complemented with another public health intervention at moderate to high effectiveness.” This could be mask use in public or continued social distancing.

Again, vaccine coverage of 90% or more of the whole U.S. population is needful for herd immunity. This may be unrealistic since sufficient vaccine doses are expected to be unavailable at the beginning, many people are indifferent about the vaccine, and a significant number of people cannot be vaccinated for medical reasons.

This lends urgency to the task of complementing vaccination with a meaningful public health intervention by universal mask use in public. With higher vaccination rates, the daily and the overall number of deaths due to COVID-19 will fall.

Effect of Social Distancing and Public Mask Use

For example, we showed that for low, moderate, and high effective social distancing, in New York, vaccination of 80%, 67% and 61%, or more, can lead to virus elimination provided social distancing is also enforced at high or moderate levels.

They also simulated the effect at the population level of combining the vaccination strategy with a public mask use strategy. They found a reduction in the value of the reproduction number Rc) as vaccine effectiveness and mask use increases – with just a 10% use of masks in public. The use of a vaccine with only 80% efficacy, vaccine coverage of 90% can eliminate the virus from the whole population.

As mask use increases to 30% or 50%, vaccine coverage of 86% and 82%, respectively, will still lead to viral elimination. The required coverage for New York State and Florida will be lower, according to this model, at around 82% to 71% vaccination for mask use of 10% and 50%, respectively.

In summary, this study shows that COVID-19 in the states of New York and Florida, as well as the entire U.S., can be eliminated even with an imperfectly effective vaccine. However, the use of other public health measures to limit community spread will significantly increase the success of virus control.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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