The US Centers for Disease Control and Prevention (CDC) partnered with Epic Research, which shares data to advance medicine and public health, to determine how effective vaccines and boosters are against hospitalisation from reinfection.
Researchers looked at electronic health records from more than 50,000 patients during both the Delta and Omicron waves who tested positive for COVID-19 more than three months after a previous infection.
“People had good immunity from (the original strain of the virus) after getting COVID the first time, but after going through the Delta period and now the Omicron period, we wanted to see what the public health impact would be,” said study author Dr Jackie Gerhart, a physician and vice president of clinical informatics at Epic Research.
During the Delta wave, they found a two-dose mRNA vaccine series was about 47% effective against hospitalisation due to reinfection, and a booster dose was more than 57% effective, according to the study published in the Morbidity and Mortality Weekly Report.
More recently during the Omicron wave, the two-dose series was about 34% effective and the booster dose nearly 68% effective. The takeaway is clear, Gerhart said.
“If you’ve previously been infected with COVID, you can get improved immunity through a vaccine and booster,” she said. “We have the tools that can help decrease your likelihood of getting reinfected and hospitalised.”
The findings suggest a booster isn’t as effective against Delta compared with Omicron, but the study authors say that may be due to the timing of the study. Data were collected during the Delta wave shortly after boosters were authorised and people may not have had time to develop the intended level of protection.
Any information from the Omicron wave is especially important now, health experts say, as its cousin BA.2 was responsible for more than 85% of new coronavirus cases last week, CDC data show.
The BA.2 variant may be a bit more transmissible but appears to mostly behave the same way as the original Omicron variant, said Dr Lyssette Cardona, department chair for infectious diseases at Cleveland Clinic Florida, Martin Health.
“Since the beginning of the pandemic, the vaccines have remained effective in preventing serious illness, regardless of the strain,” she said. “We hope that will be the same even with the different strain of Omicron.”
Cases have nationally increased by about 20% from what they were two weeks ago, with about 30 states reporting upticks, according to a USA TODAY analysis of Johns Hopkins University data. The country is averaging about 3,600 COVID-19 deaths per week.
Most of the states experiencing the biggest increases are in the north-eastern part of the country. Philadelphia has announced it will reinstate mask mandates next week as a result of the rising cases, the first city to do so this spring.
“The next month is going to be really critical to watch,” said Jodie Guest, professor and vice chair of the department of epidemiology at Emory University’s Rollins School of Public Health.
With a reported total of more than 80m COVID-19 cases since the pandemic started, more Americans are bound to get reinfected with the virus. Now more than ever, health experts say, it’s important to stay updated on COVID-19 vaccines and boosters to reduce the risk of hospitalisation.
“We expect reinfections to happen,” Cardona said. “Anyone eligible should still be vaccinated whether they had prior infection or not. Get your highest protection during this time.”
Study details
Effectiveness of COVID-19 mRNA Vaccination in Preventing COVID-19–Associated Hospitalisation Among Adults with Previous SARS-CoV-2 Infection — United States, June 2021–February 2022
Ian Plumb, Leora Feldstein, Eric Barkley3, Alexander Posner, Howard Bregman, Melissa Briggs Hagen, Jacqueline Gerhart.
Published in Morbidity and Mortality Weekly Report on 12 April 2022
Summary
What is already known about this topic?
Persons with previous SARS-CoV-2 infection have some protection against reinfection leading to hospitalisation, but there is limited evidence regarding the additional benefit of vaccination among these people.
What is added by this report?
Among those with previous infection, COVID-19 mRNA vaccination provided protection against subsequent COVID-19–associated hospitalisation. Estimated vaccine effectiveness against reinfection leading to hospitalisation during the Omicron-predominant period was approximately 35% after dose 2, and 68% after a booster dose.
What are the implications for public health practice?
To prevent COVID-19–associated hospitalisation, all eligible persons should stay up to date with vaccination, including those with previous SARS-CoV-2 infection.
Johns Hopkins data tracking of new COVID cases across USA (Open access)
See more from MedicalBrief archives:
Omicron sub-variant BA.2 warning for US as European cases surge
Vaccines provide ongoing prevention of hospitalisation and death – Large US study
UK vaccination committee says 4th booster not necessary
Boosters significantly strengthen immunity — Cov-Boost trial