In the aftermath of disasters in areas where populations live in close proximity and where sanitation and water supplies are compromised, an environment is created which is conducive to epidemics of vaccine-preventable diseases.
A strong earthquake occurred in Haiti in January 2010, severely affecting Port au Prince, the capital of the country, and the Government was functionally damaged. Over 220,000 people lost their lives and over 300,000 were injured.
Around 1.3 million people are living in temporary shelters in the Port-au-Prince metropolitan area and over 500,000 people have left the disaster areas to seek refuge in the rest of the country.
In Haiti, one of the world's most impoverished countries, the weak routine vaccination coverage was noted and the vaccination campaign was concerned as one of the first priorities.
The Japanese Red Cross (JRC) sent a medical team, called an ERU (Emergency Response Unit) right after the earthquake and provided medical services such as clinics in affected areas.
At the same time, we were involved in the vaccination campaign as one of the key players in the International Federation of the Red Cross and Red Crescent Societies (IFRC) in responding to the mass vaccination campaign by the Ministry of Health supported by WHO (World Health Organization) and UNICEF.
More than 150,000 people were vaccinated in 1 month by all Red Cross members. 35,217 of them were by JRC and the coverage was 75.5% according to the random survey. Including all the activities, it took more than 3 months and 62% of initially estimated population was vaccinated until the end.
After disasters, people typically move to other places seeking a better environment so mass vaccination campaign has to be carried out immediately, once it is decided upon. The selection of target populations, vaccines and good cooperation with other organizations is the key to success.

Objective: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant B.1.1.529 (Omicron) was first detected in Japan in November 2021. In Osaka, public health centres subsequently increased active case finding and encouraged self-isolation. This study investigated the effectiveness of these countermeasures. Methods: Cases targeted for analysis were persons who had neither recently travelled abroad nor had contact with foreign tourists but tested positive for SARS-CoV-2 between 24 November 2021 and 4 January 2022 and were suspected or confirmed to have the Omicron variant. We performed a descriptive analysis and calculated the reproduction number (R) for each generation using the branching process method. Genomic sequencing data were analysed to plot a haplotype network. Results: A total of 251 cases were analysed. The median age was 30 years, and 46% (115/251) were in their 20s or younger. The first Omicron case in Osaka was detected on 21 December 2021. Local public health centres conducted health monitoring and contact tracing. We analysed R, using information from six clusters, including 42 pairs with a clear relationship between the case and the infected contact (infector–infectee pairs); the clusters had 19, 21 and 2 cases in each subsequent generation. The basic R (t = 0) was estimated to be 3.2, and subsequent generations (t = 1, 2) of R decreased to 1.1 and 0.1, respectively. The haplotype network showed that these cases constituted a monophyletic group with others detected around Osaka, indicating that these case-related clusters had been contained and were not involved in the nationwide Omicron waves. Discussion: Active case finding and self-isolation were found to be effective in limiting the spread of an emerging novel variant.