It was a cross-sectional study, conducted in an urban area from the field practice area of a medical college from Sangli district of Maharashtra, India. The study was conducted from June 2021 to March 2022.

Institutional ethical committee approval, permissions from the relevant authorities and the written informed consent from each participant were acquired. The study population were children under the age of 5 years during March to December 2020, i.e. during first COVID-19 wave and lockdown. All the government advisory precautions on COVID-19 and lockdown were meticulously followed for the data collection.

Sampling technique applied was cluster random sampling, The municipal corporation is divided in territorial constituencies known as wards. A ward was selected randomly; mapped and visits were conducted to all the houses in the ward. In the households with children belonging to targeted age groups, parents were requested to participate in the study. The information regarding the study subjects and consent for participation was acquired from the parents/reliable informant. The exclusion criteria were non consent by parent(s), closed house and unavailability of the vaccination card at the time of data collection. If the household had more than one eligible child, then separate proforma was filled for each of them. After the completion of data collection, required vaccination counselling was given to the parents. Children who had missed vaccination at the time of data collection were noted, their parents were counselled, and with their consent, the information was shared with medical social worker (MSW) for follow-up. It was ensured with the help of MSW that those children received the missed dose and date of vaccination noted in the original data collection sheet. It was decided that the parents of children with missed vaccination, not consenting for the follow-up by the MSW and subsequent vaccination, should be considered as consent withdrawal from the study. However, we did not encounter any such case, and all the “missed” children were vaccinated. Choudhary et al. reviewed the data of NFHS-IV (2015–2016); he observed timeliness of OPV3 was lowest at 35%, i.e. delay of more than week in 65% children. Hence, 65% was considered as expected proportion for our study [9]. The calculated minimum sample size (confidence level at 99%, absolute precision at 5%) was 1434, but due to sampling method, the data was collected for 2274 study subjects.

Vaccination cards were used to confirm the dates of vaccination and date of birth of the child. For the purpose of the study, only the vaccines under Universal Immunization Programme (UIP) in the study area, until 5 years of age, were considered, and the optional vaccination or additional vaccines recommended by professional bodies like Indian Academy of Paediatricians (IAP) were not considered.

There is no universally accepted definition for “delayed vaccination”. It varies based on vaccine in question, study area and many other factors. In the literature, the definition of “delayed vaccination” varies from the strict definition of postponement of even a single day to loose definition of 30- to 90-day postponement [9,10,11]. In our study area, health facilities follow a practice of reserving a fixed day of a week for vaccination, to avoid wastage of vaccine vials and other resources (e.g. vaccination may be available every Thursday). This practice may inevitably result in a waiting period of up to 7 days from the expected date of vaccination. Hence, operational definition for the “delayed vaccination” in our study was vaccination postponement by more than 7 days from the expected date. We also took in account the minimum required interval while calculating expected date of vaccination. Hence, e.g. if dose 1 (6 week) was delayed, that does not automatically mean that dose 2 (10 weeks) was automatically delayed as the new expected date 4 weeks apart was applied.

Dose

Vaccines given under UIP (considered for this study)

Dose 0 (at birth)

BCG, OPV, hepatitis B birth dose

Dose 1 (6 weeks)

OPV-1, pentavalent-1, Rotavirus vaccine-1 (RVV), fractional dose of inactivated poliovirus vaccine (fIPV-1)

Dose 2 (10 weeks)

OPV-2, pentavalent-2, RVV-2

Dose 3 (14 weeks)

OPV-3, pentavalent-3, RVV-3, fIPV-2

Dose 4 (9 months)

Measles and rubella (MR)-1

Dose 5 (18 months)

MR-2, diphtheria-pertussis-tetanus (DPT) booster-1, OPV

Dose 6 (60 months)

Diphtheria-pertussis-tetanus (DPT) booster-2

A pretested study questionnaires was used to collect the data from the parents. The initial section of proforma had basic information like birth date of child and mother’s education; the second section was for noting dates of vaccination from vaccine cards, and final section had questions regarding attitude of parents towards vaccination and reasons for delay in vaccination, if any. Only the information regarding vaccines and reasons for their delay, if any, which were due during the March to December 2020 were noted and included in the study. The proforma was finalized after pilot study.

Analysis was done using IBM SPSS-22™ and Microsoft Excel™ 2007. For the simplicity of presentation, the data is presented in the form of doses, which represent all the vaccines given at that age; individual vaccines are not considered.

Median, interquartile range, percentage and chi-square were the statistical tests applied. Data from the pilot study and incomplete proforma were not included in the final analysis.