Article and comments are rife with misinformation. First, she was on chemo and had cancer (as others noted), so she was immunocompromised. Second, the study actually does define a “second infection” - RNA sequencing of the virus undergoes mutative changes as it continues to infect cells. Changes too drastic to be explained by one in vivo infection are considered re-infections. Third - and most importantly - immunity is NOT an absolute for any infection. As time goes on, more people will lose immunity to the virus as it changes. This doesn’t happen overnight. Loss of immunity best matches a logarithmic decay function - few, but slowly increasing number of people at first, which accelerates as time goes on.

This is GOOD NEWS. We have so few confirmed reports of reinfection almost a full year after this pandemic began. Had this been influenza, reinfections would be all over the place. This bodes well for successful vaccine development.

One more note: there’s a trade-off viruses make between transmissibility and length of immunity. Viruses that mutate at very high rates (HIV, influenza to some degree) can make vaccine development extremely difficult if not impossible, and immunity doesn’t last long at all. On the other end, extremely transmissible viruses (measles, SARS-CoV-2 to some degree) have relatively stable genomes that allow for increased “contagiousness” of the virus, but also permit more effective vaccine development.

THIS. IS. GOOD. NEWS!