Biden received a second support. That’s why it wasn’t enough to prevent infection.

President Biden has contracted the coronavirus is a stark illustration that Covid vaccines, powerful as they are, are far from the bulletproof shields that scientists once hoped for.

mr. Biden received multiple doses of the Pfizer-BioNTech vaccine; his last shot, second boosterit was March 30th. Studies show that these doses will provide powerful protection against severe illness – and indeed, according to the White House, the president has only mild symptoms so far.

But even booster doses provide little protection against infection, especially against the most recent versions of the virus. What little protection they offer disappears abruptly and quickly. research showed. In the President’s case, the booster shot he received almost four months ago has likely lost much of its effectiveness in preventing infection.

Previously during the pandemic, experts believed that vaccines would be enough to prevent not only serious illnesses, but the vast majority of infections. And that was true when earlier versions of the virus, including the Delta variant, swept the world.

But the Omicron variant overturned those hopes. As more of the population gained some immunity, whether from infection or vaccines, the virus evolved to evade that protection. BA.1, a sub-variant of Omicron that circulated during the winter, was able to cause infections even in those who had received a booster dose of the vaccine just a few weeks before.

Each subsequent avatar of the virus got better and better, bypassing immunity. BA.5, which currently accounts for nearly 80 percent of cases in the United States, is the most insidious. Detailed data collected in Qatar suggest that immunity from previous infection and vaccines weakest against BA.5 compared to their predecessors.

BA.5 is also highly contagious. The country averages about 130,000 cases per day; this number is probably a gross underestimate because most people test at home or don’t test at all.

Hospitalizations have also skyrocketed over the past few weeks, although BA.5 does not appear to cause more serious illness than other forms of Omicron.

Given how much the virus has changed, the administration is debating the value of allowing additional shots of the original vaccine in the fall. offer second boosters adults under the age of 50. FDA Advisory Group said last month that vaccine manufacturers should vaccinate with the latest options.

But it’s unclear if those shots will arrive in time to prevent an autumn surge, and if the virus will once again develop out of their reach.