Covid-19 Left U.K.'s Boris Johnson and Brazil's Jair Bolsonaro Unscathed Politically

Soon after Mr. Johnson tested positive for coronavirus on March 27, his condition worsened and he ended up in intensive care, prompting an outpouring of public support. Months later that boost has faded, opinion polls suggest, as the government he leads grapples with a fresh surge of infections.

Mr. Bolsonaro, a 65-year-old former army captain, got sick at the beginning of July, but ended up having a mild fever, a cough, and ultimately higher approval ratings.

Neither the Brazilian nor British leader, however, faced an election within a month of falling ill, and Mr. Trump had been eager to spend as much time as possible on the campaign trail with his opponent, Joe Biden, leading in polls.

In the eyes of many of his supporters in Brazil, Mr. Bolsonaro’s quick recovery substantiated his claims that Covid-19 is nothing more than a “little flu,” as he has frequently called the disease, and that the country needs to return to normal for the sake of the economy.

“It reinforced his narrative…he was lucky that his case was not serious,” said Carlos Melo, a political scientist at São Paulo’s Insper business school.

During upbeat videos posted to Facebook during his convalescence, Mr. Bolsonaro also used his illness to champion the use of the antimalarial drug hydroxychloroquine, which he has heralded as a form of miracle cure, and further vilify the press. Mr. Trump has also promoted the drug, which the U.S. Food and Drug Administration hasn’t approved as a coronavirus treatment, following evidence that pointed away from its usefulness for Covid-19 and toward cardiac and other risks.

The U.K. prime minister, who like Mr. Trump was overweight when he got ill, suffered a much more serious bout of the disease than his Brazilian counterpart. He was admitted to the hospital April 5, initially for tests after failing to shake persistent Covid-19 symptoms. His condition worsened and he was moved to an intensive care unit a day later.

The severity of his illness, coming when the pandemic raged at its fiercest, shook a country that prides itself on a cheery determination in the face of adversity, a sentiment Mr. Johnson has in the past tapped to his electoral advantage with a plucky persona and sunny optimism.

In the weeks before his hospitalization, he had exhorted Britons to sing “Happy Birthday” while washing their hands and seemed to take pride in having shaken hands with coronavirus patients and health-care staff as he visited them in the hospital. At regular news conferences he breezily assured Britons the country would “send this virus packing.”

His incapacitation and the specter of his death intensified doubts about his government’s handling of the public-health emergency and sowed concern that the country was at risk of another bout of political instability following a stormy four-year journey out of the European Union.

Public sympathy for the 56-year-old British premier boosted his personal poll ratings but didn’t affect Britons’ overall view of his government, according to analysis by pollster YouGov PLC. Mr. Johnson’s popularity rose during his hospitalization, peaking April 14 with around two-thirds of voters polled by YouGov reporting a favorable opinion of him.

He left the hospital April 12 and returned to work full-time April 27. Two days later Mr. Johnson and his fiancée Carrie Symonds announced they were expecting a baby boy. He has since urged Britons to lose weight, saying his own physical condition contributed to the intensity of his illness.

Mr. Johnson’s brush with Covid-19 chastened him, people who know him said in the weeks following his discharge from the hospital, and the experience has fueled a cautious approach from his government to relaxing restrictions on work and daily life. Some restrictions have since been reimposed as case numbers have increased. More than 42,000 people in the U.K. have died from Covid-19, the fifth-most in the world and the highest death toll in Europe.

Mr. Bolsonaro, for his part, from the beginning of the pandemic played down the risks of the virus, even as Brazil went on to become the country with the greatest number of fatalities after the U.S. Over 140,000 Brazilians have died from Covid-19.

When Mr. Bolsonaro announced he had tested positive for Covid-19 on July 7, many Brazilians who opposed the right-wing president took to social media to rejoice in the news, seeing it as the comeuppance for a leader who has often refused to wear a mask and called anyone isolating at home a “coward.”

Hours after the president’s announcement, one of the country’s biggest newspapers, Folha de S. Paulo, published a column with the title “Why I’m rooting for Bolsonaro to die,” arguing that his death might help Brazilians take the disease more seriously.

But Mr. Bolsonaro is more popular than ever. In the latest national Datafolha poll in August, 37% of respondents said they approved of the Bolsonaro administration, the best numbers he has registered since taking office in January 2019.

Political scientists largely attribute his growing popularity to his decision to hand out emergency payments to the poor during the pandemic. However, they say his contraction of Covid-19 helped consolidate support among his base, especially among evangelical Christians, who make up a third of Brazil’s population.

Ever since Mr. Bolsonaro survived a near-fatal stabbing during his campaign in 2018, many of his religious supporters believe he was chosen by God to lead the country.

His speedy recovery from Covid-19 only confirmed those beliefs, said Leonardo Barreto, a political scientist in Brasília. “It gave the impression of strength, of some extraterrestrial protection,” said Mr. Barreto.

Supporters also saw his recovery as testimony to his physical strength and virility. Mr. Bolsonaro, who likes to refer to himself as a former athlete, often performs push-ups in public engagements, a throwback to his time in the army under Brazil’s dictatorship.

—Luciana Magalhaes contributed to this article

Write to Samantha Pearson at samantha.pearson@wsj.com and Jason Douglas at jason.douglas@wsj.com