Which Vaccines Offer High Protection Against Severe COVID-19?

In UK, Pfizer-BioNTech and AstraZeneca vaccines offer high protection against severe COVID-19 even after 6 months of the second doses, finds by a study.

Protection against severe COVID-19 with two doses of the Pfizer-Bio Ntech and AstraZeneca COVID-19 vaccines remained high for up to 6 months after the second doses, new research examining NHS health record data from more than seven million adults found. Reassuringly, a University of Bristol-led study published on July 20 in the journal BMJ found protection in older adults over 65 and medically vulnerable adults.

Researchers at Bristol Medical School, UK looked at how quickly vaccine effectiveness wanes in adults without SARS-CoV-2 infection and who received the BNT162b2 (Pfizer-BioNTech) or ChAdOx1 (AstraZeneca) COVID-19 vaccine compared to unvaccinated individuals.

COVID-19 Vaccines’ Effectiveness Studied

Using linked practitioners, hospital and COVID-19 records on 1,951,866 and 3,219,349 adults who had received two doses of Pfizer-BioNTech and AstraZeneca vaccines, respectively and 2,422,980 unvaccinated adults, researchers were able to provide a clearer picture of vaccine effectiveness against COVID-19 hospital admission, COVID-19 death and positive SARS-CoV-2 test.

‘Rates of COVID-19 hospital admission and COVID-19 death were substantially lower among vaccinated than unvaccinated adults up to 6 months after their second dose.’

Rates of COVID-19 hospital admission and COVID-19 death were substantially lower among vaccinated than unvaccinated adults up to 6 months after their second dose. Vaccine effectiveness against these events was found to be at least 80% for Pfizer-BioNTech and at least 75% for AstraZeneca vaccines. However, waning vaccine effectiveness against infection with SARS-CoV-2 meant that rates in vaccinated individuals were similar to or higher than in unvaccinated individuals by 6 months after the second dose.

Dr. Elsie Horne, senior research associate in Medical Statistics and Health Data Science in Bristol Medical School: Population Health Sciences (PHS) and the study’s lead author, said: “Until now there has been limited and conflicting evidence relating to the rate of waning following second dose of COVID-19 vaccines, whether it extends to severe COVID-19, and whether the rate differs according to age and clinical vulnerability.”

“Although we found that protection against severe COVID-19 provided by two doses of vaccine wanes over time, the very high initial protection means that, despite waning, protection remains high six months after the second dose. This finding was consistent across all adults, including older adults and those who are at risk of severe COVID-19.”

Prof. Jonathan Sterne of departments of medical statistics and epidemiology in Bristol Medical School: PHS, Director of the National Institute for Health and Care Research Bristol Biomedical Research Centre (NIHR Bristol BRC) and Director of Health Data Research UK (HDR UK) South-West and co-author, added: “We found that the rate at which vaccine effectiveness waned was consistent across subgroups defined by age and clinical vulnerability. Studying how long COVID-19 vaccines remain effective continues to be important to scheduling and targeting of booster vaccinations.”

The researchers now plan to lead a follow-up study looking at vaccine effectiveness to one year post-second dose and into the era of the Omicron variant. They are also investigating the rate of waning in vulnerable clinical subgroups, such as those with chronic kidney disease and with cancer.

Source-Eurekalert