COVID vaccine protection against mild infection drops dramatically after 6 months: study

The effectiveness of the COVID-19 vaccine against omicron infection dropped dramatically after six months for people who received only their primary series, according to new analysis released Wednesday.

The study may not accurately reflect vaccine effectiveness in the United States, as researchers included many of the world’s most commonly used vaccines, including Pfizer-BioNTech, Moderna, AstraZeneca and Sinovac.

Researchers, however, have not looked at updated bivalent vaccines that target the original strain of the virus as well as BA.4 and BA.5, which are subvariants of omicron.

Meanwhile, scientists point out that vaccines still work to significantly reduce the risk of hospitalization and death. Scientists no longer expect vaccines to provide good protection against mild infections since new variants have evolved, and this is not as important due to the fact that most Americans have some level of underlying immunity.

For the analysis, published in JAMA Network Open, the team looked at 40 studies – a combination of articles and reviews published in peer-reviewed journals and preprints.

After receiving a primary series, protection against symptomatic disease decreased from 52.8% at one month after the last dose to 14.3% at six months and 8.9% at nine months.

In terms of vaccine efficacy against overall infection, protection increased from 44.4% at one month to 20.7% at six months and 13.4% at nine months.

There were some differences in the vaccine products from Pfizer and Moderna; they had higher efficacy than the AstraZeneca and Sinovac vaccines.

Dr. John Brownstein, an epidemiologist and director of innovation at Boston Children’s Hospital who was not involved in the study, said the results are not surprising because researchers have been experiencing diminishing effectiveness for some time.

“However, this study provides important insights into the specific efficacy of the original monovalent omicron vaccines and underscores the importance of the updated bivalent booster to provide additional protection,” said Brownstein, an ABC News contributor. .

Studies from the Centers for Disease Control and Protection show that updated bivalent boosters improve levels of protection.

A study found that bivalent booster reduced the risk of visiting an emergency department, urgent care facility or hospital due to COVID-19 by at least half for American adults.

Another showed that the bivalent booster provided additional protection against symptomatic infection with the two currently circulating omicron variants, XBB and XBB.1.5, for at least three months in those who had received two to four doses of the vaccine. original.

“While effectiveness against infection is an important measure, effectiveness against severe illness, hospitalization, and death are crucial measures when evaluating the overall effectiveness of COVID vaccines because these results have the most significant public health impact,” Brownstein said.

The analysis also looked at protection when receiving the initial booster dose. Protection levels have increased but also decreased.

Against infection, the effectiveness of the booster dropped from 55.4% at one month to 28.9% at nine months. Against symptomatic disease, efficacy decreased from 60.4% at one month to 13.3% at nine months.

Brownstein said it’s important to reiterate that vaccination is still very important — to protect ourselves and those at risk of serious illness — and not to interpret the study to mean that vaccines are not efficient.

As of March 19, the latest date for which CDC data is available, COVID-19 cases were 81.11 per 100,000 among unvaccinated people, compared to 26.66 per 100,000 for those vaccinated without the booster set. updated and 25.81 per 100,000 for those vaccinated with the updated booster.

Similarly, death rates as of February 26 showed a large discrepancy with 1.07 per 100,000 deaths for those unvaccinated, 0.21 per 100,000 for those vaccinated without the updated booster, and 0.19 per 100. 000 for those vaccinated with the updated booster.

“The results of this study should not detract from the importance of vaccination,” Brownstien said. “Although the effectiveness of vaccines against omicron infection may decrease over time, vaccines still provide significant protection against serious illness, hospitalization, and death.”

He added: “Additionally, booster doses can help maintain protection against the virus, particularly when they match circulating variants more closely.”

Youri Benadjaoud of ABC News contributed to this report.

Leave a Comment