* "However, both vaccines and natural immunity through prior infection were imperfect, with breakthrough infections being recorded"
A study carried out by investigators and collaborators from Qatar's healthcare system and research institutes supports previous research showing that full vaccination and prior infection are both highly effective at preventing Covid-19 and rationalises resumption of international travel in the era of the pandemic.
The research paper, published in the prestigious Journal of the American Medical Association, involved a team of researchers from the Ministry of Public Health, Hamad Medical Corporation, Weill Cornell Medicine-Qatar, and Qatar University.
Dr Roberto Bertollini, Senior Advisor to the Minister of Public Health and Deputy National Lead for Health in All Policies, and lead study investigator, explained the study aims. "Using PCR test data for residents arriving on international flights to Doha's Hamad International Airport, we assessed whether full vaccination with either Pfizer-BioNTech or Moderna vaccines, and prior infections, prevented SARS-CoV-2 infection among incoming travelers.
"In total, 261,849 people were tested on arrival at the airport and their PCR results analysed. We found that fully vaccinated individuals and people with prior infection were around 80% less likely to test positive for Covid-19 than unvaccinated individuals or those with no prior infection," explained Dr Bertollini.
These latest findings support previous research undertaken in Qatar, and recently published in the New England Journal of Medicine, as Professor Laith Abu-Raddad, Professor of Infectious Disease Epidemiology at Weill Cornell Medicine-Qatar of Qatar Foundation, explained. "The findings of this study on travelers at Hamad International Airport support our recent study showing that for fully vaccinated people, vaccination is 89.5% effective at preventing infection from the alpha variant identified originally in the UK and 75% effective at preventing infection from the beta variant identified originally in South Africa. It is very encouraging that we are seeing more and more evidence supporting the effectiveness of the Covid-19 vaccines in real world studies. The science is clear; the vaccines are highly-effective at preventing people from becoming infected, in addition to being very effective at preventing severe symptoms in the small number of people who may become infected," said Prof Abu-Raddad.
The JAMA study found that vaccination and prior infection were associated with reduced risk for a positive PRC test result among travelers, however both vaccine immunity and natural immunity through prior infection were imperfect, with breakthrough infections being recorded.
"In February this year Qatar implemented a policy which waived quarantine requirements for fully vaccinated returning residents, with vaccines recognised by the Ministry of Public Health, on condition that they produced a negative PCR test on arrival at Hamad International Airport. This policy has proved very effective at screening travelers and preventing infections coming into the country and circulating in the community while at the same time easing travel for those vaccinated," said Dr Abdullatif al-Khal, Chair of the National Health Strategic Group on Covid-19 and Head of Infectious Diseases at Hamad Medical Corporation.
"Indeed, as this latest study shows, there is still a small risk that fully vaccinated people and those with prior infection may be carrying the virus, most likely as asymptomatic carriers, and therefore these findings support Qatar's policy requiring all travelers to take a PCR test with negative result in order to waive quarantine requirements," added Dr al-Khal.
For more details on the study, 'Associations of Vaccination and of Prior Infection With Positive PCR Test Results for SARS-CoV-2 in Airline Passengers Arriving in Qatar', visit the Journal of American Medicine Association website.