The COVID-19 pandemic resulted in a reduction in the number of applied doses of the MMR vaccine as a possible effect of the restrictive actions of COVID-19. The North, Northeast and South regions and the States of Acre, Amazona, Roraima, Paraiba, Sergipe, Rio de Janeiro and Santa Catarina showed a significant reduction in the median of MMR vaccine doses applied during the period that recommendations for social distancing were put in place in Brazil. High-High spatial clusters were formed by municipalities located mostly in the Northeast and North regions of the country.
National and international studies attributed a reduction of the population's demand for health services, with a consequent drop in vaccination coverage, to the restrictive mitigation measures adopted during the COVID-19 pandemic [1, 5, 21, 22]. However, there has been an observed trend in a decline in vaccine doses applied in Brazil over the last two decades [22], especially those immunobiologicals recommended in early childhood [13, 23]. Contextual and individual factors that have been cited in recent studies [15, 22] have attributed the decline based on vaccination coverage including the lack of planning by the Brazilian National Universal Healthcare System (SUS), social and cultural aspects effecting vaccination acceptance, logistical difficulties cited by the PNI in offering several routine vaccines as part of the national vaccine schedule, anti-vaccination movements, and inconsistencies in the availability of immunobiologicals offered by Primary Healthcare services.
In this study, three of the five Brazilian regions demonstrated a statistically significant reduction in the median of doses of the MMR vaccine applied during the period of social distancing measures. This scenario, added to the drop in vaccination coverage rates in recent years, point to a problem for collective immunity and the risk of outbreaks caused by measles [14, 23]. Furthermore, it is worth noting that the regional inequalities in vaccination coverage in Brazil has favored the formation of pockets of susceptible individuals [13, 23, 24].
Between 2015 and October 2018, Brazil experienced a significant drop in MMR vaccine coverage, from 96.1 to 86.7% and, only after the national vaccination campaign, in September 2018, did it reach the 95.0% target. These low vaccination coverage indicators, added to measles cases imported from Venezuela, triggered an epidemic of the disease that affected several Brazilian states, mainly states in the Northern regions [25].
A study that evaluated the availability of the MMR vaccine in Brazil from 2013 to 2014 indicated that the immunization services located in the North region had a inefficient structure for immunization actions and demonstrated a lower frequency of vaccine availability [15]. The lack of vaccine in the Northern region, even during short period of time, incurs a lost opportunity for vaccination and can compromise the achievement of vaccination coverage goals, increasing the number of susceptible individuals in this region [15].
The lower frequency of availability of the MMR vaccine, on top of the logistical and structural problems of the AB services in the Northern region, may have contributed to the formation of clusters with a higher percentage reduction in the coverage of the MMR vaccine in this region. Furthermore, it is noteworthy that measles is one of the most contagious infectious diseases known [26], making it necessary to adopt emergency strategies for vaccinating communities that formed clusters with a significant reduction in immunization coverage during the COVID-19 pandemic period. This strategy aims to reduce the chances of overlapping cases of measles and COVID-19, which could favor the collapse of healthcare services in these regions.
Furthermore, the collapse of health services in some states in the North and Northeast regions, due to the increasing demand for hospital beds for patients with COVID-19, may have contributed to the reduction in the population's demand for immunization services in these regions [27, 28]. Strategies to contain the pandemic in states and regions of Brazil were also not uniform, which may explain the percentage variations in the median of applied doses of the MMR vaccine, from 47.52% in the State of Sergipe (p = 0.041) to 64.91% in the State of Roraima (p = 0.000). While in some locations, the response to the epidemic phase of acceleration of the number of cases and deaths from COVID-19 was the mitigation by means of social distancing, other locations resorted to the strategy of total confinement, that is suspending all non-essential activities and limiting the circulation of people [29, 30].
In Brazil, more than a year after the first case of COVID-19, the country continues to lag behind many developing countries in an effort to immunize its population against COVID-19 [31] and many public health officials agree that long-term social isolation strategies will continue for several years to come [32]. Under this scenario, it is necessary to adopt health strategies and policies that ensure the population's universal access to immunization programs. The consequences of a lack of access would means living with the overlapping cases and deaths from COVID-19 with other infectious diseases, such as measles, rubella and mumps.
Limitations and study strengths
One of the weaknesses of the present study was in relation to the intrinsic limitations of studies that use secondary data, in addition to the fact that the available data were not specifically collected to answer the questions proposed in this research. Another point that deserves to be highlighted was the possible influences related to the standardization and quality of filling in the SI-PNI records, which may be subject to information bias. However, in this study, the SI-PNI registered population data was used during the study period, and the generalization of these results is relatively safe for national estimates. Also, to control biases, methodological rigor was taken into account during all of the stages of the study execution.