Researchers Predict Whether COVID Vaccines Will Protect Against Variants

Vaccine syringes on a pink background.

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Key Takeaways

  • A new analysis found that the COVID-19 vaccine’s efficacy wanes over time.
  • The analysis also shows the vaccines may be less effective against different COVID-19 strains.
  • Experts encourage people to get their booster dose if they’re eligible.

With the constant rise of new COVID-19 variants, experts have continued to question how well the vaccines protect against these new strains. Now, researchers are trying to answer that.

A November analysis, which was published in the journal Lancet Microbe, included data from 24 studies to try to determine the level of immunity offered by COVID-19 vaccines against several virus variants.

The researchers found that the vaccines were less effective against what the World Health Organization classifies as COVID-19 variants of concern: Alpha, Beta, Gamma, and Delta than they were against the original SARS-CoV-2. They found that antibodies induced by infection were less effective against variants of concern, too.

What Is a Variant of Concern?

The Centers for Disease Control and Prevention (CDC) defines variants of concerns as those where there is evidence of an increase in transmissibility, more severe disease, and reduced effectiveness of treatments or vaccines. Currently, the CDC only lists Delta as a variant of concern.

The researchers’ models also predicted that the vaccines’ efficacy against variants over time could drop below 50% within the first year after vaccination. Over time, they saw a drop in neutralizing antibodies.

This, they concluded, suggests that booster doses of the COVID-19 vaccine are extremely important for populations as a whole to keep immunity against the virus. If people don’t get boosters, the researchers argued, protection from symptomatic COVID-19 could drop below 50% after six months. As a result, more people could get infected.

“It is likely that new COVID-19 variants will continue to emerge, as we have seen with Delta, with varying transmissibility and severity. Vaccines may not work as well against some of these variants,” Jamie Triccas, PhD, a professor of medical microbiology at the University of Sydney, said in a press release. “Essentially, we can predict how current vaccines will work against new variants, and test the efficacy of new vaccines, based on the results of small clinical trials that measure antibody responses. That’s a huge win for the battle against COVID-19.”

We're already seeing the rise of new virus variants, with reports of Omicron now spreading globally. As experts learn more about this new variant, they'll need to learn how vaccines hold up against its mutations.

But still, while vaccine immunity wanes over time, the researchers pointed out that protection against severe COVID-19 and death from the virus will likely stay high in the first year after someone is vaccinated.

"Optimal timing for boosters will depend on the availability of boosters, and whether the aim is to reduce overall case numbers or reduce the burden on the health system,” Deborah Cromer, PhD, lead study author from the University of New South Wales Sydney’s Kirby Institute, said in a statement

What Other Research Shows

Amesh A. Adalja, MD, an infectious disease expert and a senior scholar at the Johns Hopkins Center for Health Security, told Verywell that it’s “not surprising” that the most recent meta-analysis shows that the vaccine’s ability to protect against symptomatic COVID-19 wanes with time.

Richard Watkins, MD, an infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University, agrees. “The finding of the study mirror what is being seen in clinical practice, namely, that immunity wanes over time,” he told Verywell.

Research has repeatedly shown that the effectiveness of the COVID-19 vaccines reduces over time. One small study of public health data from Israel published in The Lancet in July estimated that the Pfizer-BioNTech vaccine was 39% effective at keeping people from getting COVID-19 in June and early July—a significant drop from the 95% protection they had from January to early April. Still, the researchers found, the vaccine was more than 90% effective at preventing severe disease in people, even during the summer as the Delta variant spread widely.

A study published in The Lancet analyzed data from 728,321 people in Israel who either had a third dose of the COVID-19 vaccine or the standard two-dose administration. The researchers found that the vaccine’s effectiveness was 93% after five months for those who received three doses.

The researchers concluded that having a third dose of an mRNA COVID-19 vaccine is “effective in protecting individuals against severe COVID-19-related outcomes, compared with receiving only two doses.”

Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo in New York, told Verywell that “it makes sense” that people may be able to get a year’s worth of protection with a booster shot.

“We can an annual flu shot booster as well,” he pointed out. “It’s not a big to-do if we need to get an annual booster for COVID.”

But, Russo said, “we have to track things out to see how long neutralizing antibodies last after this booster shot. It may be more than a year.”

The CDC has opened up eligibility for booster doses of the COVID-19 in the U.S. to everyone over the age of 18. People who received either the Pfizer-BioNTech or Moderna vaccine can receive a booster dose if at least six months have passed since they completed their primary vaccination series. Those who received an initial shot of the Johnson & Johnson vaccine may get a booster when at least two months have passed since their original dose.

This All May Change

Adalja said that it’s important for people to remember that the current COVID-19 vaccines are the first of their kind. “There are going to be second-generation vaccines for which this type of analysis may not necessarily apply because they may induce more and different types of immunity,” he said.

Adalja said that “there may be a role for additional doses, particularly in those with high-risk conditions at a very frequent interval like a flu vaccine, but maybe less so for those without high-risk conditions.” But, he added, “second-generation vaccines will likely have different properties and possibly not have the same frequency of dosing.”

Currently, vaccine manufacturers like Moderna and Pfizer are already developing these second-generation vaccines. Some are even aimed at specific viral variants.

Russo noted that it’s important for doctors and scientists to keep tracking the data to see how often booster doses will be needed. “At the end of the day, real-world rules,” he said.

What This Means For You

Getting your COVID-19 booster shot is the best way to make sure you’re as protected as possible against the virus. You can find an appointment hear you here.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Cromer D, Steain M, Reynaldi A et al. Neutralising antibody titres as predictors of protection against SARS-CoV-2 variants and the impact of boosting: a meta-analysis. The Lancet Microbe. 2021. doi:10.1016/s2666-5247(21)00267-6

  2. Centers for Disease Control and Prevention. SARS-CoV-2 Variant Classifications and Definitions. Updated October 4, 2021.

  3. Haas E, Angulo F, McLaughlin J et al. Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data. The Lancet. 2021;397(10287):1819-1829. doi:10.1016/s0140-6736(21)00947-8

  4. Barda N, Dagan N, Cohen C et al. Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational studyThe Lancet. 2021. doi:10.1016/s0140-6736(21)02249-2

  5. Centers for Disease Control and Prevention. Everyone Ages 18 and Older Can Get a Booster Shot. November 19, 2021.

By Korin Miller
Korin Miller is a health and lifestyle journalist who has been published in The Washington Post, Prevention, SELF, Women's Health, The Bump, and Yahoo, among other outlets.