SEOUL—Days before Wednesday’s national legislative election, candidate Ko Min-jung stood in the bed of a campaign truck slowly trawling alleys and side streets for voters.

In any other election, she and hundreds of others on the ballot would be freely addressing crowds and glad-handing supporters. Instead, Ms. Ko was ferried past darkened buildings and closed storefronts, delivering her message over a microphone wrapped in a pink polka dot slipcover.

“I can’t see your faces, but I can see your hearts and minds,” said Ms. Ko, wearing white gloves and a face mask bearing the inscription of the left-leaning Democratic Party of Korea.

South Korea is holding the world’s first national vote in a country deeply hit by the coronavirus pandemic. All 300 National Assembly seats are up for grabs, attracting dozens of political parties. President Moon Jae-in’s ruling Democratic Party, which uses the slogan “Winning the Covid-19 War,” currently holds the most seats, though not a majority.

The campaigns are an experiment in social outreach in the era of social distancing. South Korea politics look a lot different when voters are instructed to literally stay out of reach.