It’s also not clear how long first-dose protection lasts without the boost from a second dose, Dr. Fauci said during a White House press briefing in April.
“We have been concerned, and still are, that when you look at the level of protection after one dose, you can say it’s 80 percent, but it’s a somewhat tenuous 80 percent,” Dr. Fauci said. He said there’s concern that more-contagious variants that continue to spread around the globe could partially-evade vaccine-induced antibodies after just one dose. “You’re in a tenuous zone if you don’t have the full impact” of two doses, he said.
Although breakthrough infections after vaccination are rare, they do happen. A recent study of 250 people in Israel who were infected after they were partially vaccinated with the Pfizer vaccine — between two weeks after the first dose and one week after the second dose — showed that they were disproportionally infected by B.1.1.7, the variant first identified in Britain. The same study found that in a group of 149 people infected after the second dose of vaccine, eight infections with B.1.351 (the variant first identified in South Africa) occurred between days seven and 13 following the second dose. No breakthrough infections with the South Africa variant were seen 14 days after the second dose. Although it was a small sample, the finding suggested that full vaccination offers more protection against the variants, said Adi Stern, the study’s senior author, a professor at the Shmunis School of Biomedicine and Cancer Research, Tel Aviv University.
Another study showing the benefits of full vaccination looked at a group of 91,134 patients who had previously been seen by doctors in the Houston Methodist Hospital system and followed them between December and April. Most were not vaccinated, but 4.5 percent were partially immunized and 25.4 percent were fully immunized. There were 225 deaths from Covid-19 in the group, and 219 (97 percent) were among the unvaccinated. But five deaths (2.2 percent) occurred among the partially immunized. Only one person (0.004 percent) died in the fully immunized group. In that study, full vaccination was 96 protective against hospitalization and 98.7 percent protective against dying from Covid-19. But the partially vaccinated were only 77 percent protected from hospitalization and 64 percent protected from fatal Covid-19.
The study’s senior author, Saad B. Omer, director of the Yale Institute for Global Health, said he began the research with a “neutral” view about the benefits of two doses versus a single dose. But he’s now convinced the benefits of a second dose are meaningful.
“Given the data from our study and other evidence, it does not make sense for people to skip their second dose,” Dr. Omer said. “When it comes to prevention of deaths through vaccines, the glass is 64 percent full, but wouldn’t you rather have it nearly 100 percent full for such a drastic and irreversible outcome as death?”
Beyond the obvious health risks, skipping the second dose also could make your life more complicated if you want to travel or visit facilities that require proof of vaccination. “You will not be considered fully vaccinated,” Dr. Brownstein said. “It may have implications for getting back to normal again. If your vaccine passport or card doesn’t show a complete status, you may not be able to do certain things. You may not be able to get on a plane.”
