A vial of the Pfizer vaccine for COVID-19. A new...

A vial of the Pfizer vaccine for COVID-19. A new CDC study showed that vaccines sharply cut all COVID-19 infections — not just symptoms. Credit: AP / Ted S. Warren

Following pandemic news too closely can be an emotional roller coaster, with dire public health warnings immediately followed by hopeful new studies. The latest soaring discovery: a new CDC study showing vaccines sharply cut all COVID-19 infections — not just symptoms. That news puts to rest one worst-case-scenario: that vaccines might protect the vaccinated against hospitalization, but allow millions of silent infections to continue circulating.

The new data were collected from 4,000 health care workers, first responders, delivery workers and teachers who were vaccinated with the Pfizer or Moderna vaccines between December 2020 and March 2021. The participants were asked not only to monitor symptoms but also to test themselves weekly. The study authors concluded the vaccines caused a 90% reduction in all infections. If people aren’t getting infected, they can’t transmit the virus to others.

The next drop on the roller coaster could come from new virus variants, some of which have shown ability to evade antibodies generated by the original strain. But experts such as Paul Offit of the Children’s Hospital of Philadelphia are more optimistic. The vaccines show some efficacy against all the currently known variants, and good efficacy against one — the B.1.1.7 strain identified in the U.K. last year.

Even before the new study came out, Offit saw enough other evidence of decreased transmission from vaccines that he said he liked the idea of issuing vaccine passports for travel, restaurants or other venues. Data from Israel, where most of the population is already vaccinated, show rapidly dropping deaths and hospitalizations. "Nothing is foolproof," he says, but people will be much safer mixing with others who are vaccinated than those who are not.

The new study results should also allay fears that the vaccines’ astounding clinical trial results wouldn’t hold up in the real world. One concern was a small sample size. While there were thousands of people enrolled in those trials, infections were relatively uncommon so only a small number of people became infected in either the vaccine arm or the placebo group.

In this new study, there were 161 infections in the control group of 994 unvaccinated people. By contrast, among the 2,479 vaccinated participants, only eight became infected between their first and second doses, which are given three or four weeks apart. Only three people were infected after they were fully vaccinated (two weeks after receiving the second shot).

One reason Offit said he was so optimistic was that the vaccines induce not just antibodies, but so-called cellular immunity. That is, they stimulate production of specialized virus-fighting cells called T-cells, which can work against a broader range of variants than antibodies. The T-cells also last longer than antibodies and are what give vaccines the power to "remember" and fight a pathogen weeks or even months later.

He was also enthusiastic about the Johnson & Johnson vaccine, though it was only used in five people in the CDC study. That vaccine induces cellular immunity after just one shot, he says, while the Pfizer and Moderna vaccines induce T-cells only after two shots. (For that reason, he does not advise skipping the second shot of the two-shot vaccines in order to conserve supply.)

Monica Gandhi, an infectious disease doctor at UCSF, said that she thinks the shots will effectively end the pandemic because the T-cells can fight different variants. "I do understand it almost seems too good to be true that the vaccines will get us out of this," she says. "But they will."

One thing we’ve learned is that it’s hard to predict the course of this pandemic — given how hard it is to predict human behavior and the fast evolutionary path of the virus. Even the vaccine optimists such as Gandhi and Offit don’t see eradication of the virus in sight. But they do see the possibility the virus could become less of a threat to life and health than seasonal flu, after which it will be hard to hold back a return to normal life — one with restaurants, international travel, and yes, roller coasters.

Faye Flam is a Bloomberg Opinion columnist and host of the podcast "Follow the Science." She has written for the Economist, the New York Times, the Washington Post, Psychology Today, Science and other publications.