Although vaccination is carried out worldwide, the vaccination rate varies greatly. As of 24 May 2021, in some countries, the proportion of the population fully vaccinated against COVID-19 has exceeded 50%, but in many countries, this proportion is still very low, less than 1%. This article aims to explore the impact of vaccination on the spread of the COVID-19 pandemic. As the herd immunity of almost all countries in the world has not been reached, several countries were selected as sample cases by employing the following criteria: more than 60 vaccine doses per 100 people and a population of more than one million people. In the end, a total of eight countries/regions were selected, including Israel, the UAE, Chile, the United Kingdom, the United States, Hungary, and Qatar. The results find that vaccination has a major impact on reducing infection rates in all countries. However, the infection rate after vaccination showed two trends. One is an inverted U-shaped trend, and the other is an L-shaped trend. For those countries with an inverted U-shaped trend, the infection rate begins to decline when the vaccination rate reaches 1.46–50.91 doses per 100 people.

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Methamphetamine is a prevalent recreational drug among men who have sex with men (MSM) living with HIV and could cause the cognitive impairment and memory loss. However, studies on the association between methamphetamine use and adherence to antiretroviral treatment (ART) are limited and had inconsistent findings. This study aimed to determine the impact of methamphetamine use on adherence to ART among MSM living with HIV. From December 2018 to October 2019, MSM living with HIV were recruited (N = 351) and non-adherence to ART was defined as a Medication Adherence Report Scale score of <23. Overall, 16.0% of the participants reported methamphetamine use in the prior three months and 13.4% of the participants had non-adherence to ART. The proportion of non-adherence to ART among HIV-positive MSM were 28.6% and 10.5% with and without methamphetamine use, respectively. After controlling for demographics, illicit drug use, and comorbidities, methamphetamine use during the prior three months was associated with a higher risk of non-adherence to ART (adjusted odds ratio = 3.08; 95% confidence intervals: 1.24-7.69). Compared with HIV-positive MSM with non-adherence to ART, HIV-positive MSM with good adherence to ART had a higher CD4 counts and were more likely to achieve an undetectable viral load. Since poor adherence to ART is associated with an increased HIV viral load and the risk of HIV transmission to others, our study suggests that it is imperative to screen HIV-positive patients for methamphetamine use and to provide effective therapy to reduce methamphetamine use and the associated non-adherence to ART.As of 2018, there are 37.9 million people living with HIV/AIDS (PLWHA) worldwide 1 . The widespread use of antiretroviral therapy (ART) has significantly decreased the risk of opportunistic infections and mortality among PLWHA 2,3 . Although ART could markedly improve the survival in PLWHA, treatment compliance to ART plays