New York, Mar 30 (IANS): Pfizer-BioNTech and Moderna's Covid-19 vaccines are highly effective in preventing infections in real world conditions, says a new study by the US Centers for Disease Control and Prevention (CDC).

Results showed that following the second dose of vaccine, risk of infection was reduced by 90 per cent two or more weeks after vaccination, the CDC said on Monday.

Following a single dose of either vaccine, the participants' risk of infection with SARS-CoV-2 was reduced by 80 per cent two or more weeks after vaccination.

The study looked at the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines in preventing SARS-CoV-2 infections among nearly 4,000 participants in six US states over a 13-week period from December 14, 2020 to March 13, 2021.

It takes about two weeks following each dose of vaccine for the body to produce antibodies that protect against infection.

As a result, people are considered "partially vaccinated" two weeks after their first dose of mRNA (Messenger RNA)

vaccine and "fully vaccinated" two weeks after their second dose.

These new vaccine effectiveness findings are consistent with those from phase-3 clinical trials conducted with the vaccines before they received Emergency Use Authorisations from the US Food and Drug Administration (FDA).

Those clinical trials evaluated vaccine efficacy against Covid-19 disease, while this study evaluated vaccine effectiveness against infection, including infections that did not result in symptoms.

"This study shows that our national vaccination efforts are working. The authorised mRNA Covid-19 vaccines provided early, substantial real-world protection against infection for our nation's health care personnel, first responders, and other frontline essential workers," CDC Director Rochelle Walensky, said in a statement.

This study also provided positive news about partial (one-dose) vaccination.

The estimate of 80 per cent effectiveness in this study is consistent with other recent studies following the first dose of Pfizer-BioNTech vaccine among health care providers.

Studies conducted in the UK and Israel showed that one dose was about 70 per cent and 60 per cent effective, respectively, against SARS-CoV-2 infection.

The current results provide reassurance that people start to develop protection from the vaccine two weeks after their first dose.

The greatest protection was seen among those who had received both recommended doses of the vaccine.