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This study aimed to compare the occurrence and nuisance of adverse events following administration of each COVID-19 vaccine dose between two groups: individuals given three doses of mRNA vaccine (homologous group, 3 × mRNA, n = 252) and those given two doses of adenoviral vector vaccine further boosted with mRNA vaccine (heterologous group, 2 × AZ + 1 × mRNA, n = 205). Although the studied groups differed significantly in the frequency and number of side effects after the first and second vaccine dose, no relevant differences were seen following the booster administration. Arm pain and fatigue were the most common effects, regardless of the vaccination group and vaccine dose. In the homologous group, female sex, lower BMI, and no history of regular influenza vaccination were associated with a higher frequency of side effects of a booster dose. In the heterologous group, the history of COVID-19 was associated with an increased number of side effects seen after a booster. In both groups, the number of side effects related to the first and second dose correlated with the number observed after administration of a booster dose. Individuals receiving a homologous booster reported a higher nuisance of side effects than the heterologous group. It was similar to the level reported after the second dose in both groups. The use of pharmaceuticals to counteract the side effects was more frequent after a first dose in the 2 × AZ + 1 × mRNA group, but higher after second dose in individuals receiving the 3 × mRNA vaccination scheme. The frequency of pharmaceutical use after a booster dose was similar in both groups (approx. 60%). Paracetamol was most frequently chosen, regardless of the group and vaccine dose. In addition, the vast majority of participants (93%) declared to accept future doses of the COVID-19 vaccine if their administration would be recommended. This study provides an overview of the response to homologous and heterologous mRNA vaccine booster dose that may be valuable in shaping accurate and honest communication with vaccinated individuals, especially in those regions which are yet to pursue booster strategies.

COVID-19 vaccinations are essential to mitigate the pandemic and prevent severe SARS-CoV-2 infections. However, the serum antibody levels in vaccinated individuals gradually decrease over time, while SARS-CoV-2 is undergoing an evolution toward more transmissible variants, such as B.1.617.2, ultimately increasing the risk of breakthrough infections and further virus spread. This cross-sectional online study of adult Poles (n = 2427) was conducted in September 2021 (before a general recommendation to administer a booster COVID-19 vaccine dose in Poland was issued) to assess the attitude of individuals who completed the current vaccination regime toward a potential booster dose of the COVID-19 vaccine and identify potential factors that may influence it. Overall, 71% of participants declared willingness to receive a booster COVID-19 dose, with a low median level of fear of receiving it of 1.0 (measured by the 10-point Likert-type scale), which was increased particularly in those having a worse experience (in terms of severity of side effects and associated fear) with past COVID-19 vaccination. The lowest frequency of willingness to receive a booster dose (26.7%) was seen in the group previously vaccinated with Ad26.COV2.S. The majority of individuals vaccinated previously with mRNA vaccines wished to receive the same vaccine, while in the case of AZD1222, such accordance was observed only in 9.1%. The main reasons against accepting a booster COVID-19 dose included the side effects experienced after previous doses, the opinion that further vaccination is unnecessary, and safety uncertainties. Women, older individuals (≥50 years), subjects with obesity, chronic diseases, and pre-vaccination and post-vaccination SARS-CoV-2 infections, and those with a history of vaccination against influenza were significantly more frequently willing to receive a booster COVID-19 dose. Moreover, the majority of immunosuppressed individuals (88%) were willing to receive an additional dose. The results emphasize some hesitancy toward potential further COVID-19 vaccination in the studied group of Poles and indicate the main groups to be targeted with effective science communication regarding the booster doses.

Pursuing vaccinations against COVID-19 brings hope to limit the spread of SARS-CoV-2 and remains the most rational decision under pandemic conditions. However, it does not come without challenges, including temporary shortages in vaccine doses, significant vaccine inequity, and questions regarding the durability of vaccine-induced immunity that remain unanswered. Moreover, SARS-CoV-2 has undergone evolution with the emergence of its novel variants, characterized by enhanced transmissibility and ability to at least partially evade neutralizing antibodies. At the same time, serum antibody levels start to wane within a few months after vaccination, ultimately increasing the risk of breakthrough infections. This article discusses whether the administration of booster doses of COVID-19 vaccines is urgently needed to control the pandemic. We conclude that, at present, optimizing the immunity level of wealthy populations cannot come at the expense of low-income regions that suffer from vaccine unavailability. Although the efficiency of vaccination in protecting from infection may decrease over time, current data show that efficacy against severe disease, hospitalization, and death remains at a high level. If vaccine coverage continues at extremely low levels in various regions, including African countries, SARS-CoV-2 may sooner or later evolve into variants better adapted to evade natural and vaccine-induced immunity, ultimately bringing a global threat that, of course, includes wealthy populations. We offer key recommendations to increase vaccination rates in low-income countries. The pandemic is, by definition, a major epidemiological event and requires looking beyond one’s immediate self-interest; otherwise, efforts to contain it will be futile.

COVID-19 vaccinations are about to begin in various countries or are already ongoing. This is an unprecedented operation that is also met with a loud response from anti-vaccine communities—currently using all available channels to manipulate public opinion. At the same time, the strategy to educate on vaccinations, explain their mechanism of action, and build trust in science is subdued in different world parts. Such actions should go much beyond campaigns promoting the COVID-19 vaccines solely on the information provided by the health institutions and national authorities. In this paper, actions provided by independent expert groups needed to counteract the anti-vaccine propaganda and provide scientific-based information to the general public are offered. These actions encompass organizing groups continuously communicating science on COVID-19 vaccines to the general public; tracking and tackling emerging and circulating fake news; and equipping celebrities and politicians with scientific information to ensure the quality of messages they communicate, as well as public letters, and statements of support for vaccination by healthcare workers, recognized scientists, VIPs, and scientific societies; and no tolerance to false and manipulated claims on vaccination spread via traditional and social media as well as by health professionals, scientists, and academics. These activities should be promptly implemented worldwide, regardless of the current status and availability of the COVID-19 vaccine in a particular region. If we are about to control the pandemic for the sake of public benefit, it is high time to collectively speak out as academic and medical societies with support from decision-makers. Otherwise, the battle will be lost to those who stand against scientific evidence while offering no feasible solution to the problem.