Almost four years after Protein Sciences began selling its innovative flu vaccine, the Meriden company still struggles to gain a foothold in a marketplace dominated by pharmaceutical powerhouses. Orders for Flublok – the only flu vaccine not derived from eggs – remain well below company goals, and officials haven’t been able to get it into some major pharmacy chains such as CVS and Walgreens. “We’re doing better than last year, but we’re still not doing as well as I would like to do,” said CEO Manon Cox. The company aims to sell 900,000 doses of Flublok by the end of the current flu season in late March, she said. So far, it has sold just 250,000, even as widespread flu outbreaks spread across several parts of the country.