A new large-scale study in the United States shows that two doses of the Pfizer vaccine are up to 90% effective in preventing hospitalization for at least six months, even among individuals infected with the Delta variant.
According to the study, the effectiveness against infection from all variants of SARS-CoV-2 decreased from 88% (after receiving two doses) to 47% after six months. However, the effectiveness against hospitalization remains high at 90% across all variants, including Delta, as reported by The Guardian on October 5.
The researchers emphasized that these results highlight the importance of improving global COVID-19 vaccination rates.
The Pfizer/BioNTech COVID-19 vaccine is highly effective in preventing severe illness for at least six months after receiving both doses.
“Our study confirms that vaccines are a crucial tool for controlling the pandemic and remain highly effective in preventing severe illness and hospitalization,” said the lead author of the study, Dr. Sara Tartof, from the Kaiser Permanente Southern California Research and Evaluation Department.
The researchers analyzed health records of 3 million people from December 2020 to August 2021.
During the study period, 5.4% of vaccinated individuals contracted SARS-CoV-2.
Among those infected, 6.6% required hospitalization. The average time from full vaccination to infection was between three to four months.
The study found that while the Pfizer vaccine’s effectiveness against infection from the Delta variant decreased by 40% within five months, the protection against hospitalization related to all variants remained very high throughout the study period.
These findings, published in The Lancet, align with preliminary data from the Centers for Disease Control and Prevention (CDC) and the Ministry of Health in Israel.
Dr. Luis Jodar, Senior Vice President and Chief Medical Officer of Pfizer’s vaccine division, stated: “Our specific analysis of the variants clearly shows that the Pfizer vaccine is effective against all currently concerning variants, including Delta.”
“The infections of COVID-19 in individuals who have received two doses of the vaccine are most likely due to the waning (of vaccine effectiveness over time), rather than Delta or other variants having the ability to evade vaccine protection.”
“Our findings underscore the importance of monitoring vaccine effectiveness over time and indicate that booster doses may be necessary to restore the high levels of initial protection recorded during the vaccination program,” according to the study.
In August, U.S. authorities approved booster shots for individuals with weakened immune systems, while France also approved this for older adults.
Israel took a further step, offering booster shots to individuals aged 12 and older after five months of receiving their second dose.
However, a report in September from the World Health Organization (WHO) indicated that current COVID-19 vaccines are sufficiently effective to combat the risk of severe illness, and booster shots are not necessary for the general population.
Last month, WHO called for a temporary halt on COVID-19 booster vaccinations until the end of the year to address severe inequalities in dose distribution between rich and poor countries.
