The withdrawal of Jamaica's Jackson, who had already skipped the 100m won by St Lucia's Alfred on Saturday, follows that of compatriot Shelly-Ann Fraser-Pryce from the shorter sprint.
Jackson, bronze medallist in the 100m in Tokyo three years ago, suffered an apparent injury in a meet in Hungary three weeks ago and had said her decision to miss the 100m was best for her "body, mind and soul".
Alfred's main threat now is likely to come from Tokyo Olympics 200m bronze medallist Gabby Thomas of the United States.
Alfred looked fresh, despite the emotion of winning St Lucia's first-ever Olympic medal.
She was so far ahead of her rivals she eased down 40 metres from the line, timing 22.41 seconds and still finished comfortably ahead of the runner-up, Gemima Joseph of France.
Alfred is attempting to match Jamaica's Elaine Thompson-Herah, who did the 100m-200m sprint double in Rio in 2016, repeating the feat at the Tokyo Games.
Thomas eased through her heat in a time of 22.20sec with her teammate, Brittany Brown, qualifying for the semi-finals in a time of 22.38sec.
The 29-year-old, who won 200m silver at the 2019 world championships but appearing at her first Olympics, said she had had a few rough years, with the Covid pandemic a factor.
"It took a bit of getting back on my feet and then I changed coaches and I think that it's all come together," she said.
"So it's been nice to have that feeling of like, you know, when everything arrives at the same time."
Brown's conqueror from Doha, Dina Asher-Smith, is seeking her first individual medal in her third appearance at Olympics.
The 28-year-old European 100m champion was eliminated at the semi-final stage of the shorter sprint on Saturday and used that disappointment to fuel her.
But the British sprinter finished a relaxed second in her heat on Sunday.
"I'm really happy with that," said Asher-Smith. It was really easy. I ran angry.
"My coach (Edrick Floreal) and I are just taking one round at a time. I know I'm in great shape."
The 200m semi-finals are scheduled for 1845 GMT on Monday, with the final listed for 1940 on Tuesday.
