The majority of subjects in each group were women (61

The majority of subjects in each group were women (61.5%C65.0%, value = 0.961). (= 20). A booster dose of a COVID-19 vaccine was strongly associated with maintained or increased COVID-19 antibody levels. The booster dose was also more strongly associated with antibody responses than the primary vaccination series. Among patients receiving a booster dose of a mRNA vaccine or a heterologous regimen, antibody levels remained steady or even increased for 3 to 6 months after symptom onset compared with inactivated or viral Prochlorperazine vector vaccines. There was a strong correlation between anti-RBD IgG and neutralizing antibodies against the Delta variant. This study is relevant to resource-limited countries for administering COVID-19 vaccines 3 to 6 months after infection. Keywords: antibody response, booster, COVID-19 vaccine, neutralizing antibody, waning of immunity 1. Introduction Between the emergence of coronavirus disease 2019 (COVID-19) in late 2019 and the beginning of August 2022, over 582 million cases of infected patients and approximately 6.4 million deaths have been reported [1]. The primary cause was severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The precise and rapid diagnosis of this viral infection has been globally accepted as the key to successful treatment outcomes. Comprehensive vaccine administration is one of effective methods to prevent the progression of COVID-19, lower the mortality, and control disease transmission [2,3,4]. In many countries, a mRNA vaccine (PfizerCBioNTech BNT162b2) was the first COVID-19 vaccine. The vaccine was given emergency use authorization by the United Prochlorperazine States Food and Drug Administration on 11 December 2020. The organization officially approved the vaccine on 23 August 2021 [5]. In Thailand, COVID-19 vaccines first became available in February 2021. The main types were inactivated vaccines (CoronaVac and Sinopharm) and an adenovirus vector vaccine (ChAdOx1 nCoV-19, AstraZeneca). A small batch of the BNT162b2 (PfizerCBioNTech) vaccine was initially delivered in July 2021, some of which was retained for research. The mRNA-1273 (Moderna) vaccine started being delivered in November 2021. This meant that Thais could increasingly access mRNA COVID-19 vaccines. However, by late 2021, many Thais had already received a primary series based on the inactivated and adenovirus vector vaccines available from February 2021. Further vaccination with the mRNA vaccines was encouraged even if individuals had already been infected because the inactivated and adenovirus vector vaccines did not provide robust immunity [6,7]. BMP10 People that are infected with SARS-CoV-2 develop natural immunity which consists of humoral and cellular immunity. The antibody responses can be detected within the first week after the onset and last only a few weeks to several months before declining [8,9,10,11,12]. Neither the past infection nor vaccination provided lifelong protection against reinfection incidence. Booster vaccination doses were, therefore, considered a critical strategy to maintaining high levels of immune response and preventing reinfection at that time (around 2020C2021) [11,13]. Although the advantages of COVID-19 vaccination seem convincing, some patients hesitate or refuse to receive vaccines, either as primary series or booster doses. Their reluctance stems from the current lack of scientific data on the long-term effects of the COVID-19 vaccines [14]. The levels of antibodies (anti-spike immunoglobulin G [IgG], anti-receptor binding domain [RBD] IgG, anti-nucleocapsid IgG, and neutralizing antibodies) have become measurable indicators and have been widely reported [15,16]. Nevertheless, there was still limited evidence that patients receiving at least one booster dose after SARS-CoV-2 infection have stronger immunity than those without a booster dose around mid to late 2021. Siriraj Hospital, Thailand, implemented home isolation and hospital-affiliated hotel isolation (hospitel) management strategies for Prochlorperazine patients with asymptomatic and mild to moderate COVID-19 in the second trimester of 2021. Longitudinal data on the humoral immune responses of patients with SARS-CoV-2 infections can be helpful and may be associated with some clinical data. The results may materially affect vaccination recommendations and patients judgments on whether to receive a booster dose, especially in a resource-limited country. This study aimed to evaluate the dynamics of antibody responses for various vaccination statuses during the 6 months following a COVID-19 illness. Moreover, we examined the correlation between the responses of anti-RBD IgG and neutralizing antibodies against the Wuhan and Delta (B.1.617.2) variants of SARS-CoV-2. This arises from the concern over whether neutralizing antibody against the Delta strain may be.