In the past few months, steady headline news has highlighted the amazing effectiveness of Covid-19 vaccines in the field, particularly mRNA vaccines from Pfizer-BioNTech and Moderna. Studies have shown that the vaccines are more than 90 percent effective in preventing the worst outcomes, including hospitalization and death.
But alongside this good news, there have been rare reports of severe Covid in fully vaccinated people.
For example, on June 3, Napa County announced that a fully vaccinated woman who was more than a month after her second Moderna shot had died after being hospitalized with Covid. The over 65-year-old woman with previous illnesses had tested positive for the alpha variant identified for the first time in Great Britain.
While these cases are tragic, they are unusual – and not unexpected.
"I am very sad that she had such a serious illness that she actually died," said Dr. William Schaffner, medical director of the National Foundation for Infectious Diseases and vaccines expert at Vanderbilt University. But, he said, "we expected the occasional breakthrough infection to occur."
Such cases shouldn't prevent people from getting vaccinated, scientists said. "There is no vaccine in history that has ever been 100 percent effective," said Dr. Paul Offit, the director of the Vaccine Education Center at Children's Hospital of Philadelphia. “This is your best chance to avoid serious, critical illness. But as with everything in medicine, it is not perfect. "
Severe Covid is rare in fully vaccinated people. In a paper released last month, the Centers for Disease Control and Prevention said they had received reports of 10,262 breakthrough infections as of April 30. That's only a tiny fraction of the 101 million Americans who have been vaccinated as of that date, though the agency found these were likely to be a "significant minority" of breakthrough infections.
Of these groundbreaking cases, 10 percent of patients were hospitalized and 2 percent died – and in some of those cases, patients were hospitalized or died of something unrelated to Covid-19. The average age of the deceased was 82 years.
June 9, 2021, 6:05 p.m. ET
Older adults, who are at a higher risk of Covid complications, are also more likely to develop breakthrough infections as they are known to build weaker immune responses to vaccines. People with weakened immune systems or other chronic illnesses may also be at increased risk.
Some of the variants – especially beta, which was first identified in South Africa – may be more likely to evade vaccine-induced protection. But beta isn't common in the United States right now, noted Dr. Conductor.
The alpha variant that infected the Napa County woman is highly contagious, but vaccines offer good protection against it – as well as against the original strain of the virus.
"Vaccines offer exceptional protection against death and disease from the virus, and all residents should continue to be vaccinated to protect themselves and others," said Dr. Napa County's health officer Karen Relucio in a statement.
Breakthrough infections are likely to decline as more people are vaccinated and community transmission rates decline. "The virus will find fewer and fewer people to infect – it will be more difficult for the virus to get through the population," said Dr. Conductor. “These are great vaccines. So that the vaccines work optimally – individually and collectively – as many people as possible must be vaccinated. "