CSV Splitter in Bash

I am splitting a csv file where the first 3 columns will be common for all the output files.

input file:

h1 h2 h3 o1 o2 ....
a  b  c  d  e  ....
a1 b1 c1 d1 e1 ....

output files:

o1.csv:

h1 h2 h3 o1
a  b  c  d  
a1 b1 c1 d1  

o2.csv:

h1 h2 h3 o2
a  b  c  e
a1 b1 c1 e1 

So if there are n columns in the input file , the code creates n-3 output files. However my code is inefficient and is quite slow. It takes 20 seconds for 50000 rows.

old_IFS=$IFS
START_TIME=`date`
DELIMITER=,           

# reading and writing headers    
headers_line=$(head -n 1 "$csv_file")
IFS=$DELIMITER read -r -a headers <<< $headers_line
common_headers=${headers[0]}$DELIMITER${headers[1]}$DELIMITER${headers[2]}

for header in "${headers[@]:3}"
do
   # writing headers to every file
   echo $common_headers$DELIMITER$header > "$header$START_TIME".csv
done

# reading csv file line by line
i=1
while IFS=$DELIMITER read -r -a row_data
do
    test $i -eq 1 && ((i++)) && continue      # ignoring headers

    j=0

    common_data=${row_data[0]}$DELIMITER${row_data[1]}$DELIMITER${row_data[2]}
    for val in "${row_data[@]:3}"
    do
        #  appending row to every new csv file
        echo $common_data$DELIMITER$val >> "${headers[(($j+3))]}$START_TIME".csv
        ((j++)) 
    done

done < $csv_file
IFS=${old_IFS}

Any suggestions are appreciated.