using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var d = JsonConvert.DeserializeObject<PatientImmunization>(json);

        Console.WriteLine(string.Join(",", d.Immunizations.Select(x => x.DateOfDose)));     

    }

    static string json = @"{

    'Immunizations': [{ 

            'VaccineName':'HPV',

           'DateOfDose': '2021-01-2'

        },

        {

            'VaccineName': 'P23',

            'DateOfDose': '2021-01-23'

        },

        {

            'VaccineName': 'P23',

            'DateOfDose': '2000'

        }

    ]

}";

    public class PatientImmunization

  {

​

    /// <summary>List of patient immunization records</summary>

    public List<ImmunizationRecord> Immunizations { get; set; }

  }

    public class ImmunizationRecord

  {

    /// <summary>Vaccine Name</summary>

    public string VaccineName { get; set; }

​

    /// <summary>Date of Dose</summary>

    public DateTime? DateOfDose { get; set; }

  }

}