CDC Studies Show Vaccine Protection Wanes Over Time, Less Effective Against Delta Variant

The Centers for Disease Control and Prevention Wednesday released three studies on the effectiveness of the Pfizer and Moderna vaccines. A UK study released Tuesday showed people with “breakthrough” infections carry as much virus as the unvaccinated.

New COVID vaccine data released Wednesday by the Centers for Disease Control and Prevention (CDC) confirms COVID vaccine effectiveness against infection has decreased over time, and is less effective in combating the Delta variant.

“The data we will publish today and next week demonstrate the vaccine effectiveness against SARS CoV-2 infection is waning,” CDC Director Dr. Rochelle Walensky said during a press briefing. “And even though our vaccines are currently working well to prevent hospitalizations, we are seeing concerning evidence of waning vaccine effectiveness over time, and against the Delta variant.”

The CDC released three new studies focusing on the vaccines’ effectiveness in light of the Delta variant.

One study assessed Pfizer and Moderna’s effectiveness over time against infections among nursing home residents, and found it dropped from 75% pre-Delta to 53% when Delta became dominant. The study didn’t differentiate between asymptomatic, symptomatic and severe infections.

Another study used data from 21 hospitals to estimate the effectiveness of Pfizer and Moderna mRNA vaccines against hospitalization over time. Among 1,129 patients who received two doses of a mRNA vaccine, vaccine effectiveness was 86% 2 to12 weeks after vaccination and 84% at 13 to 24 weeks.

The third study, using New York state data, found all three vaccines’ effectiveness against infection dropped from 92% in early May to 80% at the end of July, but the effectiveness against hospitalization remained relatively stable.

Data from the three reports in the CDC’s Morbidity and Mortality Weekly Report, helped convince the Biden administration to recommend booster shots to people eight months after receiving their second dose, despite no completed late-stage clinical trials assessing the safety, efficacy and immunogenicity of a third dose.

Under Biden’s plan announced Wednesday, boosters will start being administered Sept. 20 — pending authorization of a third dose from the U.S. Food and Drug Administration and the CDC’s advisory committee.

Health experts said the CDC data should make the case that it’s more important to get initial doses to the unvaccinated, and boosters to immunocompromised people and nursing home residents, rather than to the entire population.

“I mostly care about hospitalizations, I don’t care about infections because this is not what we’re using vaccines for. We’re not trying to stop infections, and there’s no evidence that a third booster will stop infections,” said Jennifer Nuzzo, an epidemiologist and senior scholar at the Johns Hopkins Center for Health Security.

Nuzzo said people need to remember vaccines aren’t force fields. “They don’t prevent infections,” she said. “They train your immune system to respond quickly to infections and hopefully limit the number of cells that get infected. They work to limit infections to prevent severe disease, hopefully to keep people out of the hospital.”

Celine Gounder, an infectious disease doctor at Bellevue Hospital Center and former adviser on COVID to the Biden campaign, said, “It makes sense to give an extra dose of vaccine to vaccinated nursing home residents, but what will have an even bigger impact on protecting those nursing home residents is to vaccinate their caregivers.”

President Biden announced Wednesday he is ordering the U.S. Department of Health and Human Services to require nursing homes to have vaccinated staff, or lose federal Medicare and Medicaid funding.

The new vaccination requirement comes after the Biden administration announced July 30 that federal government, civilian federal employees and contractors would be required to show proof of vaccination against COVID or submit to regular COVID testing, wear masks and socially distance.

Fully vaccinated people with ‘breakthrough’ infections carry as much virus as the unvaccinated

A British public health study released Aug. 16, indicates vaccinated people with “breakthrough” infections could pose a significant infection risk to those who have not been vaccinated, CBS News reported.

study by University of Oxford scientists found people who contract the COVID Delta variant after being fully vaccinated carry a similar amount of the virus as those who catch the disease and have not been vaccinated.

The study also found protection was greatest in those vaccinated who already had natural immunity through previous infection.

The study evaluated effectiveness of Pfizer, AstraZeneca and Moderna COVID vaccines in a large community-based survey of randomly selected households across the UK.

Based on more than 3 million nose and throat swabs, Oxford University researchers found that 90 days after a second shot of the Pfizer or Astrazeneca vaccine, efficacy in preventing infections had slipped to 75% and 61% respectively.

Those results were down from 85% and 68%, respectively, seen two weeks after a second dose, with the decline in efficacy more pronounced among those 35 years and older.

The study also showed that after two doses of the Pfizer vaccine, effectiveness was at least as great as protection afforded by natural infection — with greater initial effectiveness against new PCR-positives but faster declines in protection against high viral burden and symptomatic infection.

Researchers said there was no evidence effectiveness varied by dosing interval, but protection was higher among those vaccinated who already had natural immunity.

“With Delta, infections occurring following two vaccinations had similar peak viral burden to those in unvaccinated individuals,” the study concluded.

Viral “burden,” or viral load, refers to how much SARS-CoV-2 virus infected people carry and thus “shed,” or release into the environment around them, where it can potentially infect others.

The survey, which has yet to be peer-reviewed before publication in a scientific journal, underscores concerns by scientists that the Delta variant can infect fully vaccinated people at a greater rate than previous variants, and that the vaccinated could more easily transmit it, Reuters reported.

Oxford’s lead researcher, Dr. Sarah Walker, told The Telegraph the study shows two doses of the Pfizer, Moderna or AstraZeneca vaccines are still protective. “You are still less likely to get infected — but if you do, you will have similar levels of virus as someone who hasn’t been vaccinated at all,” Walker said.

The data used for the study do not show how likely it is that a fully vaccinated person with the Delta variant can pass on the infection to another individual, compared to an unvaccinated individual with the virus.

But the high viral loads found in the study are a strong indicator that the risks of transmission from both vaccinated and unvaccinated people with the Delta variant could be similar, CBS reported.

Despite the study’s results, the message from Walker and Oxford team was clear: Vaccination remains the best way to protect against infection and serious illness or hospitalization with COVID, including the Delta variant.

The research was funded by the Wellcome Trust — funded by a $29.1 billion investment portfolio — which  partners with the World Health Organization, Bill & Melinda Gates Foundation and World Economic Forum, and has direct public equity holdings in Microsoft, Google, Facebook and Johnson & Johnson.