Most refugee minors and their respective families came from Kiev and larger Easter Ukrainian cities and were generally well educated. These findings are consistent with a larger-scale nation-wide survey in Germany in 2022 (11,753/48,000 Ukrainians contacted by post), with 80% female participants, 72% with university degree and about a third came from Charkiv (15%) or Kiev (19%). The predominance of women in both surveys results from the fact that men were only allowed to leave Ukraine if they were fathers of more than three children or had a handicapped child [1].

During the same period, we conducted a study of minors who had grown up in Germany, in which the same questionnaire was used to assess their general and mental health. Although two different populations are never exactly comparable, the German minors showed markedly better results (“at least good” general health 93% (732/783); mental health 91% (707/777)) [21, 22]. Reasons for poorer health perception could be traumatic experiences of armed conflict, flight and uprooting [3]. Well-being has been linked to regular school or daycare attendance [1], which emphasizes the need for rapid integration. However, it remains essential to investigate psychological distress and to provide psychological diagnostics and treatment if necessary in the native language [23].

Most reported diseases were bronchitis, congenital anomalies and developmental delay (each around 5%), other chronic diseases like bronchial asthma and diabetes mellitus corresponding with 1.3% and 0.5% to the prevalence reported for Ukraine [6], while epilepsy was less frequent with only 1.3% [7]. None of these diseases was more common in German minors.

Importantly, underweight (< P3) seemed to be more common in Ukrainian minors and might represent a significant health problem (11% vs. 7.5%, p < 0.05 [24]) with almost a quarter of under 7-year-olds affected. Therefore, growth and weight monitoring should be given special attention in care of Ukrainian minors. Interestingly, we noticed a discrepancy between the incidence of underweight (e.g. 13–18 years 2.1% instead of 5.3%, p = 0.1) and obesity (e.g. 13–18 years 12.8% instead of 3.2%, p < 0.01) when using the WHO percentiles compared to the percentiles published for Ukraine in 2018 [25], illustrating the lack of comparability between country-specific percentiles and WHO standards [26].

Regarding the data on SARS-CoV-2 in Ukrainian minors in comparison to the German minors from our studies mentioned above, antibodies against SARS-CoV-2 were detectable more often (spike antibodies 87.5% vs. 85.5%; nucleocapsid antibodies 88% vs. 67.2% [21]), while T cellular response were less often positive (IGRA 45.9% vs. 67.6% [27]), most likely due to a lower vaccination rate resulting in hybrid immunity.

In addition to vaccine hesitancy in Ukraine, lack of vaccine availability and the delayed implementation due to the war probably played a role. The role of cellular immune response for protection against SARS-CoV2 is still unclear, but vaccination—at least for the risk of chronically ill minors—is for Germany, for example strongly recommended [28].

Although TB incidence among Ukrainian minors is lower than in adults (1.8% vs. 10.9%) [29], it is still higher than in minors living in Germany (estimated incidence 7/100,000 vs. 1.3/100,000, [11]). With regard to the high prevalence of TB and very high level of drug-resistance in Ukraine, the low rate of positive TB IGRA in minors seems to be reassuring. However, it could also be biased by an assumable better socioeconomic status of this group. The risk to develop potentially infectious TB within the first 2 years after immigration is increased in refugees. Therefore, we recommend TB screening for all Ukrainian minor refugees in line with national regulations, even if they do not live in shared accommodation. History of contact had not been a reliable source of information in our cohort (e.g. for two children from different families, known TB was reported, but only one person reported household contact with TB).

The incidences for HIV (0.3%) and hepatitis C (0.5%) were higher than in age-matched German minors, but below expected occurrence of up to 1% HIV and 3.6% hepatitis C [15,16,17]. Multiple cases per family were also a rarity (HIV and hepatitis C 0.7% of cases each). Only for hepatitis C, several new diagnoses among the accompanying adults were detected, while most HIV and hepatitis B infections were already known. Screening for infectious diseases like HIV, hepatitis B and C should nevertheless be offered to all minors and their families [6, 15, 30].

Testing serological correlates of protection against vaccine-preventable diseases combined with a survey of respective history of vaccination status were essential parts of this study. In Ukraine, vaccinations are usually only documented by the healthcare provider who administered them [30], so many of our participants did not have a vaccination record. Therefore, the accuracy of the individual immunization history becomes important. History of chickenpox is a reliable marker for serological correlate of protection against varicella, while for other vaccine-preventable diseases history of infection insufficiently correlates with protection.

While we found broad antibody prevalence for polio, tetanus, diphtheria, haemophilus influenzae and mumps, serological protection against measles, varicella and hepatitis B is much lower. In principle, all undocumented and necessary vaccinations should therefore be carried out in accordance with the recommendations of the WHO [31] or the host countries (e.g. [28]).

We would like to focus on measles and hepatitis B in detail as examples.

Measles vaccination is one of the most important international public health intervention available, with > 90% effectiveness [32]. In Germany—as example for Western Europe—vaccination rates for measles are high with 97.4% for 1st vaccination [33], whereas serological protection rate against measles in the study cohort was lower (84.4%) and far below the WHO > 95% target. In a previous European survey, 86% of mothers from nine countries stated that their children had been vaccinated [34] and a German study [33] reported that 7.7% (6.5–9.1) of parents did not have their children vaccinated for fear of side effects. In Ukraine on the other hand, vaccine hesitancy has been very high [35]. Only after a large national measles outbreak in 2018 causing notable mortality in children, measles vaccination rates did increase [6], which is also certainly responsible for the decline in measles antibodies from the age of 12 years. Therefore, catch-up measles vaccination for this population seems to be mandatory.

Following the introduction of universal hepatitis B (HBV) vaccination in Ukraine, initially vaccination rates were high but subsequently decreased considerably (92–98% (2004–2007) vs. 21–48% (2010–2016) [30]). We found a serological correlate of protection against hepatitis B in less than 50% in Ukrainian minors ≥ 12 years, considerably lower than in age-matched Germans (84.4%) [33]. Therefore, especially adolescents should be offered HBV vaccination.

In addition to the possible selection bias (like high education and urban background of the Ukrainians included), there are some limitations to our findings. Although our cohort is the largest of its kind, it may not appropriately represent the Ukrainian refugee population. In addition to this, most of our data are survey based, so despite trained interpreters, it is limited in its validity. Furthermore, surveys of parents to assess child health always face the problem that the perception of the child itself might not be reflected. Not all participants were followed up, meaning that it is not possible to report detailed follow-up information. In addition, severity of illness and effects of interrupted medical care on the course of the illness were not recorded since invasion and flight until immigration to Germany.