COVID-19 Roundup: Vaccine Studies Show Waning Protection Against Infection, But Still Strong Against Hospitalizations

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August 20, 2021

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New CDC Studies That Spurred Booster Plan Show Vaccine Protection Against Infection is Waning

Fully vaccinated individuals retain enough protection against hospitalization from COVID-19, according to three new studies from the U.S. Centers for Disease Control and Prevention (CDC) which reinforce previous research on the vaccines’ effectiveness against serious illness.

However, the new studies suggest that this protection against serious illness may decline over time. The research provided the primary impetus for U.S. health officials to announce a rollout next month of booster doses for those vaccinated with the two-shot vaccines from Pfizer-BioNTech or Moderna.

The CDC made sure to remind the public that the currently authorized vaccines provide more than adequate effectiveness against COVID-19 hospitalization for now — even if someone gets infected with the dominant Delta variant after being vaccinated.

“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,” said CDC Director Rochelle Walensky, M.D., during a press briefing this week.

One of the studies examined the “overall age-adjusted vaccine effectiveness against hospitalization in New York State” from May 3 through July 25 of this year. Vaccine effectiveness against hospitalization in New York was relatively stable (91.9 percent – 95.3 percent). The overall age-adjusted vaccine effectiveness against infection — or so-called breakthrough infections — for all New York adults declined from 91.7 percent to 79.8 percent, the CDC found.

The findings suggest currently available vaccines have high effectiveness for preventing infection and COVID-19 hospitalization, the CDC said. “However, vaccine effectiveness against infection appears to have declined in recent months … coinciding with a period of easing societal public health restrictions and increasing Delta variant circulation,” the agency added.

CDC researchers were not able to determine precisely if the drop in effectiveness against infections was because of the Delta variant, or because people reduced masking and social-distancing, or if the reduction in effectiveness resulted from an actual drop in immunity.

Data from the three CDC reports helped convince U.S. public health officials to recommend booster shots for people already vaccinated with the Pfizer or Moderna vaccines starting next month. The third shots should be administered at least eight months after receiving the second shot, officials said.

Related article: U.S. Health Officials: COVID-19 Booster Shots Likely to Begin Rollout for Everyone in September

Like Pfizer, Moderna Says Its Vaccine Remains as Effective 6 Months After Second Dose

Moderna reports that the protection provided by its COVID vaccine does not diminish much six months after the second dose. Nonetheless, both Moderna and Pfizer-BioNTech are moving forward with seeking U.S. approval for booster shots, which will likely begin a rollout to eligible individuals next month, U.S. officials said this week.

Moderna’s findings were based on a new review of a clinical trial launched more than a year ago with more than 30,000 volunteers across the United States. In November, Moderna reported that its two-shot vaccine provided 94.1 percent protection against COVID. That percentage didn’t change much after six months, the company stated.

“We are pleased that our COVID-19 vaccine is showing durable efficacy of 93 percent through six months, but recognize that the Delta variant is a significant new threat so we must remain vigilant,” Stéphane Bancel, the chief executive officer of Moderna, said in the statement.

Moderna’s report also said that “robust antibody responses have been observed from existing Moderna booster candidates against COVID-19 in Phase 2 studies.”

The makers of the other, two-shot mRNA vaccine available in the U.S., Pfizer-BioNTech, reported recently that its vaccine’s efficacy wanes only slightly six months after the second dose, but still provides lasting and strong protection against serious illness, hospitalization and death from COVID. Like Moderna, Pfizer executives say a third shot, or booster, could improve immunity and is likely to be available — at least to high-risk individuals, before the end of the year.

An advisory group to the U.S. Centers for Disease Control and Prevention (CDC) is considering whether fully vaccinated Americans with weakened immune systems need a booster dose of the Pfizer or Moderna vaccines.

The U.S. Food and Drug Administration (FDA) is expected to give full approval to the Pfizer-BioNTech vaccine next month. Moderna filed for final approval designation of its vaccine on June 1, and expects to complete its submission date this month.

Initial trials considered by the FDA before issuing the current “emergency use authorizations” found the Moderna and Pfizer vaccines to be up to 95 percent effective in preventing COVID-19 illness in those without prior infection. The single-shot Johnson & Johnson vaccine, also available under emergency use authorization, was found to be 86 percent effective against severe disease by the FDA.

Study: Vaccines Strongly Protect Those 65-Plus Against Hospitalization

New findings of a recent study of hospital data found that the three available COVID-19 vaccines in the U.S. were highly effective in preventing severe illness and hospitalization in adults 65 years of age or older.

Researchers monitored COVID-19 patients 65 and older between February 1 and April 30. According to the study, the two-dose Pfizer-BioNTech and Moderna vaccines reduced the risk of hospitalization by 96 percent in adults 65-74 years old. The single-dose Johnson & Johnson vaccine lowered the risk of hospitalization by 84 percent for adults of the same age range. A previous study released by the CDC reported similar results.

“In this analysis of 7,280 laboratory-confirmed COVID-19 cases among hospitalized adults aged 65 or older, all three COVID-19 vaccine products currently authorized for use in the United States had high effectiveness in preventing COVID-19–associated hospitalizations,” states the CDC.

These findings are consistent with estimates from other observational studies of the mRNA vaccines from Pfizer and Moderna, and provide an early estimate of the effectiveness of Johnson & Johnson vaccine in preventing COVID-19–associated hospitalization. The CDC study covered a period of time before the delta variant become the dominant COVID-19 strain. However, other studies since then have shown that all three vaccines continue to provide robust protection against severe illness against the more transmissible delta variant.

The data included in the study’s analysis were from: California, Colorado, Connecticut, Georgia, Maryland, Michigan, Minnesota, New Mexico, New York, Ohio, Oregon, Tennessee, and Utah.