Why no one should skip the second dose of the COVID-19 vaccine (Marijan Murat/dpa via AP) While Washington state fights slowing COVID-19 vaccine demand and tries to fill the gap between those fully vaccinated and the threshold for herd immunity, people who do not go back for their second dose are creating another challenge. According to statistics released by the Washington State Department of Health, about 13% of Washingtonians who get the two-dose Pfizer or Moderna — which require three weeks and four weeks in between doses, respectively — are behind on getting their second dose. Just under 5% never got it at all.