There’s an urban myth that when it comes to painting Australia’s Sydney Harbour Bridge once you start you never stop. While that’s not completely true, painting does conform to a schedule. That’s how you stop the rust and rot. And it’s a simile only now being thrust on the world in the vaccine fight against Covid-19. Earlier this week the New England Journal of Medicine published long-term efficacy numbers for the Pfizer and Moderna mRNA Covid-19 vaccines. It told us that while both drugs produced good antibodies against infection, that protection only lasted six months after their second dose. In other words, a person fully immunised today would be covered against serious Covid-19 infection but only till October this year. Thing is, nobody is…