A vaccine scare ripples around the world: The week in Covid-19 news.

Safety worries about the AstraZeneca and Johnson & Johnson Covid-19 vaccines in the United States and Europe have reverberated around the world, undercutting faith in two sorely needed shots and threatening to prolong the coronavirus pandemic in poorer countries that cannot afford to be choosy about vaccines. With new infections surging on nearly every continent, signs that the vaccination drive is in peril are emerging, most disconcertingly in the continent of Africa.

In many African countries, vaccination campaigns have been hindered by factors like science skepticism, limited or no efforts to educate the public, inefficient distribution systems and concerns over the extremely rare but serious cases of blood clots being investigated among a small number of people who received the AstraZeneca and Johnson & Johnson vaccines. Those two vaccines, which require less stringent refrigeration, are crucial to efforts to immunize populations in poorer countries.

But in Malawi, some people are asking doctors how to flush the AstraZeneca vaccine from their bodies. In South Africa, health officials have stopped giving the Johnson & Johnson shot, two months after dropping the AstraZeneca vaccine because it was less effective against the dominant variant there.

Across the continent, public confusion over whether to get inoculated — and if so when and where to do so — has contributed to the expiration of doses. South Sudan saw 59,000 unused doses expire this month, and in the Democratic Republic of Congo, 1.7 million AstraZeneca doses have gone unused.

The actions of U.S. and European officials have stoked doubts in poorer countries where a history of colonialism and unethical medical practices have left a legacy of mistrust in vaccines. If the perception takes hold that rich countries are dumping second-rate shots on poorer nations, those suspicions could harden, slowing the worldwide rollout of desperately needed doses.

Here’s what else you may have missed:

  • In India, about 32 million people were driven into poverty by the pandemic last year, according to the Pew Research Center — accounting for a majority of the 54 million who slipped out of the middle class worldwide. A second wave of Covid-19 is threatening the dreams of millions more looking for a better life.

  • Keeping the middle seats vacant during a flight could reduce passengers’ exposure to airborne coronavirus by 23 to 57 percent, researchers reported in a new study. This reduction in risk stemmed from increasing the distance between an infectious passenger and others as well as from reducing the total number of people in the cabin. But the study may have overestimated the benefits of empty middle seats because it did not take into account mask-wearing by passengers.

  • More exercise means less risk of developing severe Covid, according to a compelling new study of physical activity and coronavirus hospitalizations. The study found that those who had been the most active before falling ill were the least likely to be hospitalized or die as a result of their illness.