Milena Silva Souza

To the Editor: In this Journal, Antonelli and colleagues reported the positive clinical impacts of booster COVID-19 vaccine usage in vulnerable groups and posited that these observations should encourage vaccine uptake.1 According to the World Health Organization (WHO), more than 13.6 billion COVID-19 vaccine doses have been administered worldwide since 2021.

Abstract This study evaluated tilapia fed diets supplemented with levels of betaine and l-carnitine, simultaneously. Diets supplemented with levels of l-carnitine (500 and 1000 mg kg−1 of feed) and betaine (500 and 1000 mg kg−1 of feed) were used, in addition to the control diet. Weight gain, daily weight gain, and specific growth rate in fish fed diets containing 1000–500 and 1000–1000 mg kg−1 betaine and l-carnitine performed worse than the other inclusion levels, including the control diet.

1 INTRODUCTION More than 763 million people have been affected globally by the Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)1 since its emergence, resulting in more than 6.9 million deaths.2 The numbers of COVID-19 cases have diminished mainly due to the progress of vaccination3, 4 using antigens based on the wild-type (WT) virus.