# Is a COVID-19 Vaccine Likely to Make Things Worse?

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## Abstract

**:**

## 1. Introduction

## 2. Methods

**Remark**

**1.**

## 3. Results

#### 3.1. Parameter Estimates

#### 3.2. Before Vaccination

#### 3.3. After Vaccination

#### 3.4. Threshold Behaviour

#### 3.5. Discussion

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**PRCCs before vaccine introduction for (

**a**) 75–80% and (

**b**) 85–90% levels of transmissibility. The outcome variable is the daily risk of infection before vaccination, ${r}_{1}$.

**Figure 2.**PRCCs for limiting cases: (

**a**) non-compliance with physical distancing rules, (

**b**) shortage of face masks and (

**c**) no hand sanitizing. The outcome variable is the daily risk of infection before vaccination, ${r}_{1}$, and we consider high transmissibility ($0.85\le \beta \le 0.90$).

**Figure 3.**Sensitivity of the daily risk of COVID-19 to transmission rates when the only protection option available is the vaccine. (

**a**) The red dots represent the pre-vaccination risk of infection, while the blue dots represent the post-vaccination daily risk. The fraction of people getting vaccinated, ${q}_{7}$, ranges from 0.25 to 1. (

**b**) The outcome variable is the daily risk of infection after vaccination, ${r}_{2}$, and the fraction of people vaccinated, ${q}_{7}$, ranges from 0 to 0.2 (purple dots), from 0.2 to 0.4 (orange), from 0.4 to 0.6 (yellow), from 0.6 to 0.8 (green) and from 0.8 to 1 (light blue).

**Figure 4.**Sensitivity of the daily risk of COVID-19 to (

**a**) vaccine uptake ($0.25\le {q}_{7}\le 1$), (

**b**) the fraction of people using no protection, (

**c**) vaccine efficacy and (

**d**) the ideal scenario of perfect vaccine uptake (${q}_{7}=1$). Note the reduced scale on the y-axis in the last figure. The transmission rate $\beta $ is between $0.7$ and 1.

**Figure 5.**Boxplots of 1000 sampled values using the LHS ranges from Table 1, except with ${q}_{7}$ varying and other ${q}_{i}$ values set to zero. The horizontal red line indicates the median value. We present the daily risk of COVID-19 under three scenarios: (

**a**) before the vaccine; (

**b**) after the vaccine but with imperfect vaccine uptake ($0.25<{q}_{7}<1$); and (

**c**) after the vaccine and with perfect vaccine uptake (${q}_{7}=1$).

**Figure 6.**Sensitivity of the threshold level, ${r}^{*}$, to vaccine uptake, ${q}_{7}$. The transmission rate $\beta $ ranges between $0.7$ and $0.75$ (brown dots) or between $0.85$ and $0.90$ (pink).

**Figure 7.**PRCCs after vaccine introduction. (

**a**) Vaccination is the only option available; (

**b**) all options and their combinations are in use; (

**c**) when physical distancing is not possible; (

**d**) when masks are not available. All values are as in Table 1, except that we constrained $0\le {q}_{7}\le 0.142$ in (

**b**–

**d**).

**Table 1.**Parameter values before and after vaccine introduction. We assumed a uniform use of all available protection protocols (including no protection) before the vaccine. Thus, there are eight possible combinations of protection protocols: ${p}_{0}$ through ${p}_{6}$ and no protection ($1-{p}_{0}-{p}_{1}-{p}_{2}-{p}_{3}-{p}_{4}-{p}_{5}-{p}_{6}$). The upper bound of the range of values for each proportion is equal to 0.125. After the introduction of a vaccine, we considered both the extreme case where vaccination was the only available protection option ($0<{q}_{7}<1$) and the vaccine in combination with other protection options (with upper bound 0.142, including ${q}_{7}$).

Parameter | Definition | Range |
---|---|---|

$\beta $ | Transmissibility | 0.7–1 |

${e}_{D}$ | Physical distancing | 0.21–0.78 |

${e}_{M}$ | Face coverings | 0.2–0.9 |

${e}_{H}$ | Handwashing | 0.24–0.31 |

${e}_{V}$ | Vaccine efficacy | 0.85–1 |

${p}_{0}$ | Fraction of people practicing only physical distancing | 0–0.125 |

${p}_{1}$ | Fraction of people only wearing face coverings | 0–0.125 |

${p}_{2}$ | Fraction of people only practicing regular handwashing | 0–0.125 |

${p}_{3}$ | Fraction of people practicing physical distancing and | |

wearing face coverings | 0–0.125 | |

${p}_{4}$ | Fraction of people practicing physical distancing and | |

regular handwashing | 0–0.125 | |

${p}_{5}$ | Fraction of people wearing face coverings with regular handwashing | 0–0.125 |

${p}_{6}$ | Fraction of people practicing physical distancing with regular | |

handwashing and wearing face coverings | 0–0.125 | |

${q}_{0}$ | Fraction of people only practicing physical distancing post-vaccination | 0 |

${q}_{1}$ | Fraction of people only wearing face coverings post-vaccination | 0 |

${q}_{2}$ | Fraction of people only practicing regular handwashing post-vaccination | 0 |

${q}_{3}$ | Fraction of people practicing physical distancing and | |

wearing face coverings post-vaccination | 0 | |

${q}_{4}$ | Fraction of people practicing physical distancing and | |

regular handwashing post-vaccination | 0 | |

${q}_{5}$ | Fraction of people wearing face coverings with regular | |

handwashing post-vaccination | 0 | |

${q}_{6}$ | Fraction of people practicing physical distancing with regular | |

handwashing and wearing face coverings post-vaccination | 0 | |

${q}_{7}$ | Fraction of people using only the vaccine | 0–1 |

${q}_{8}$ | Fraction of people using the vaccine and practicing physical distancing | 0–0.142 |

${q}_{9}$ | Fraction of people using the vaccine and wearing face coverings | 0–0.142 |

${q}_{10}$ | Fraction of people using the vaccine with handwashing | 0–0.142 |

${q}_{11}$ | Fraction of people using the vaccine, practicing physical distancing | |

and wearing face coverings | 0–0.142 | |

${q}_{12}$ | Fraction of people using the vaccine, practicing physical distancing | |

with handwashing | 0–0.142 | |

${q}_{13}$ | Fraction of people using the vaccine, wearing face coverings | |

with handwashing | 0–0.142 |

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**MDPI and ACS Style**

Abo, S.M.C.; Smith?, S.R. Is a COVID-19 Vaccine Likely to Make Things Worse? *Vaccines* **2020**, *8*, 761.
https://doi.org/10.3390/vaccines8040761

**AMA Style**

Abo SMC, Smith? SR. Is a COVID-19 Vaccine Likely to Make Things Worse? *Vaccines*. 2020; 8(4):761.
https://doi.org/10.3390/vaccines8040761

**Chicago/Turabian Style**

Abo, Stéphanie M. C., and Stacey R. Smith?. 2020. "Is a COVID-19 Vaccine Likely to Make Things Worse?" *Vaccines* 8, no. 4: 761.
https://doi.org/10.3390/vaccines8040761