Study: Pfizer vaccine protects against hospitalization for six months

The Pfizer-BioNTech coronavirus vaccine is 90 percent effective in preventing hospitalization for up to six months, with no signs of decline during this time, according to a large new American study conducted by researchers at Pfizer and Kaiser Permanente.

The vaccine also offers potent protection against the highly contagious Delta variant, the scientists found. In a subset of people who had samples of their virus sequenced, the vaccine was 93% effective against hospitalization of Delta, compared with 95% against hospitalization of other variants.

“Protection from hospitalization remains high over time, even when Delta is predominant,” said Sara Tartof, epidemiologist at Kaiser Permanente Southern California and first author of the study.

However, the vaccine’s effectiveness against infection declined over time, from 88 percent in the first month after vaccination to 47 percent after five months.

The findings, published in The Lancet on Monday, come amid a debate over whether and when booster shots may be needed. The Food and Drug Administration has authorized boosters for Pfizer vaccine recipients who are 65 years of age or older or at high risk of infection or serious illness. And the Biden administration has been pushing for boosters to be more widely available to the general public.

But many scientists and public health experts have backed down, arguing that the country’s priority should be to vaccinate people who have not yet been vaccinated and that vaccines still seem to offer good protection against the worst consequences, including serious illness and death.

Data from Israel indicates that the effectiveness of the Pfizer vaccine against infection fell to 39 percent in late June and early July, from 95 percent from January to early April. But it remained over 90 percent effective against serious illness during that time.

On the other hand, a recent study from the Centers for Disease Control and Prevention reported that the vaccine’s effectiveness against hospitalization fell to 77 percent after four months, compared to 91% in the first few months.

In the new study, researchers analyzed the electronic health records of more than 3.4 million members of Kaiser Permanente Southern California, between December 14, 2020 and August 8, 2021.

Overall, the vaccine was 90 percent effective against hospitalization and 73 percent against infection. Among those who were 65 years or older, it was 86% effective against hospitalization and 61% against infection.

Researchers have sequenced more than 5,000 samples of the virus. Overall, the Delta variant accounted for 28% of these samples, although it was the dominant variant in June and July.

The vaccine was slightly less effective against Delta than the other variants, providing 75 percent protection against Delta infection, compared to 91 percent protection against the other variants.

But protection against infection has declined at a similar rate over time, the researchers found. After four months, the efficacy against infection had fallen to 53% against Delta and 67% against the other variants.

The findings could fuel both sides of the adjunct debate, Dr Tartof said.

“The question is, what do you want your booster program to do? ” she said. Some may say that this data supports boosters, as it shows an increase in breakthrough infections over time, she said. Others, however, might point out the vaccine’s constant protection against serious illness and argue that boosters are not necessary.