By Pushkala Aripaka (Reuters) -Britain’s health regulator on Wednesday approved the country’s first two-pronged COVID-19 booster targeting the Omicron BA.4 and BA.5 sub-variants and the original coronavirus strain. The Medicines and Healthcare products Regulatory Agency (MHRA) said the vaccine from Pfizer and partner BioNTech was approved for use as a booster in people 12 years and older after it was found to meet safety, quality and effectiveness standards. Britain had already approved so-called bivalent vaccines targeting the Omicron BA.1 sub-variant from Pfizer-BioNTech and rival Moderna, b…